ITEMS FROM MEXICO

 

International Maize and Wheat Improvement Center - CIMMYT

Lisboa 27, Colonia Juárez, Apdo. Postal 6-641, 06600, México, D.F., México.

Free threshing bread wheat/synthetic hexaploid derivatives resistant to Fusarium graminearum.
[p.93-96]

A. Mujeeb-Kazi and R. Delgado.

Synthetic hexaploid wheats that are the products of crosses between T. turgidum and Ae. tauschii are the basic germ plasm sources for screening of entries with resistance/tolerance to biotic and abiotic stresses. Once desired germ plasm lines are identified, the next step is introgressing the trait into elite but stress-susceptible bread wheat cultivars. Head scab in bread wheat is one stress for which genetic diversity is limited and is a disease of major concern in the high-rainfall mega-environments. We have identified several synthetic hexaploids that express good, type-II resistance and many of these were crossed into leading bread wheat cultivars several crop cycles ago. The resulting progenies of these crosses were advanced by the pedigree method, and selections were advanced if they possessed a level of scab resistance similar to or better than Sumai 3 and also had resistance to leaf and stripe rusts. In addition, all lines had stem rust resistance, with resistance to S. tritici, Karnal bunt, and H. sativum considered a bonus.

Scab screening was done in Toluca, Mexico, and the germ plasm was tested for several years. Selections were directed towards free-threshing, agronomically suitable plant types in order to facilitate further breeding options. Selections focused on scab type-II (spread) resistance data plus other complimentary traits. The yearly crop harvest in October in Toluca was taken to Obregon for a November planting and May harvest, after which the advanced generation materials were retested in Toluca during the June-October crop cycle.This shuttle breeding, adopted from our main wheat-breeding program protocol, allowed for desirable outputs as to quality disease-resistant plants that were photoperiod insensitive. We currently maintain 143 elite lines for scab resistance and several from later crosses that are in the F4 generation. The involvement of various Ae. tauschii accessions in the pedigrees of the derivatives indicate a wide array of genetic diversity that should be beneficial for imparting durability of scab resistance to bread wheat germ plasm.

Some of the best of the 143 lines over multiyear testing are included in Table 1, and the most promising, less-advanced F4 materials are listed in Table 2. The inoculation and scoring protocols were standard and are described in detail by Mujeeb-Kazi and Delgado on page 97 of this issue.

Table 1. Fusarium head scab data (type II - spread) of some superior advanced bread wheat/synthetic hexaploid derivatives from multiyear evaluations in Toluca, Mexico. Ae. tauschii accession number in wheat wide crosses working collection are in parentheses. Bread wheat cultivars in pedigrees are indicated by the superscript BW the first time they occur in one of the pedigrees.

2001 Entry No.	Pedigree	Infection Score (%)
		1998	1999	2000	2001
1	Mayoor (resistant bread wheat)	11.3	12.9	8.5	13.5
4	Flycatcher (susceptible bread wheat)	30.7	40.5	28.5	31.3
10	Mayoor//TKSN1081/Ae. tauschii (222)	8.2	11.9	6.2	9.5
14	Mayoor//TKSN1081/Ae. tauschii (222)	11.0	13.5	10.3	10.0
19	Mayoor//TKSN1081/Ae. tauschii (222)	12.6	7.0	7.9	7.6
23	Mayoor//TKSN1081/Ae. tauschii (222)	12.6	11.9	12.0	9.8
26	Mayoor//TKSN1081/Ae. tauschii (222)	13.1	9.3	9.6	12.6
37	Mayoor//TKSN1081/Ae. tauschii (222)	10.2	7.7	9.6	13.6
50	Mayoor//TKSN1081/Ae. tauschii (222)	11.8	9.6	12.7	8.7
53	Mayoor//TKSN1081/Ae. tauschii (222)	9.2	12.0	11.2	13.4
65	BCN^BW^//Ceta/Ae. tauschii (954)	13.0	14.8	6.3	9.1
67	BCN//Croc1/Ae. tauschii (662)	12.4	12.0	11.4	10.0
68	BCN//Doy1/Ae. tauschii (447)	12.0	12.0	11.0	8.9
69	BCN//Doy1/Ae. tauschii (447)	13.0	11.4	5.8	7.3
72	Altar 84/Ae. tauschii (224)//2*Yaco^BW^	10.2	10.5	8.8	8.9
78	Croc1/Ae. tauschii (224)//2*Opata^BW^	11.2	11.9	11.4	10.8
79	Opata/6/68.111/RGB-u//Ward/3/FGO/4/Rabi/5/Ae. tauschii (878)	9.2	8.7	12.0	8.2
80	Opata//Croc1/Ae. tauschii (879)	12.5	14.2	9.0	12.8
82	SabufBW/5/BCN/4/Rabi//GS/CRA/3/Ae. tauschii (190)	6.9	13.1	9.8	10.4
83	Sabuf/3/BCN//Ceta/Ae. tauschii (895)	11.0	14.0	13.1	12.6
84	Sabuf/3/BCN//Ceta/Ae. tauschii (895)	7.8	14.0	8.4	11.2
90	Chir3*/5/CS/Th.curvifolium//Glen/3/ALD/PVN/4/CS/L. racemosus//2*CS/3/CNO79BW	11.0	13.4	11.7	8.6
98	Mayoor/5/CS/Th. curvifolium//Glen/3/ALD/PVN/4/CS/L. racemosus//2*CS/3/CNO79	8.9	10.1	9.1	11.9
101	Chirya.1BW	6.9	9.7	9.0	7.9
102	Chirya.3BW	12.2	12.7	6.1	10.2
103	Chirya.3	6.0	13.3	--	10.2
107	CNO79//Ruff/Ae. tauschii/3/Maize	8.4	14.8	12.7	9.1
113	PJNBW/BOWBW//Opata*2/5/YAV-3/SCO//Jo69/CRA/3/YAV79/4/Ae. tauschii (498)	10.2	9.8	7.5	11.7
117	PJN/BOW//Opata*2/3/GAN/Ae. tauschii (437)	9.8	10.9	12.8	11.3
130	Rabi//GS/CRA/3/Ae. tauschii (190)/4/MirloBW/BUCBW//VEE#7^BW^	10.1	11.8	13.4	9.4
138	Dverd 2/Ae. tauschii (1026)/3/Mirlo/BUC//VEE#7	8.3	9.0	9.2	8.3
141	Rabi//GS/CRA/3/Ae. tauschii (190)/4/PJN/BOW//Opata	9.2	9.6	10.8	12.0

Table 2. Fusarium head scab (type II - spread) data of 14 advanced bread wheat/synthetic hexaploid derivatives following 2 years of evaluations in Toluca, Mexico. Ae. tauschii accession number in wheat wide crosses working collection are in parentheses. Bread wheat cultivars in pedigrees are indicated by the superscript BW the first time they occur in one of the pedigrees.

2001 Entry No.	Pedigree	Days-to-flowering	Height (cms)	Infection Score (%)
				2000	2001
6	BCNBW/Doy1/Ae. tauschii (447)	90	115	12.5	10.4
7	Altar 84BW/Ae. tauschii (224)//2*Yaco^BW^	82	120	5.1	10.4
8	SabufBW/3/BCN//Ceta/Ae. tauschii (894)	90	125	6.3	11.0
9	Sabuf/5/Bcn/4/Rabi//GS/CRA/3/Ae. tauschii (190)	85	125	10.7	10.8
11	PJN*/BOW//Opata*2/3/GAN/Ae. tauschii (437)	82	125	10.7	13.2
12	Rabi//GS/Cra/3/Ae. tauschii (190)/4/PJN/BOW//Opata^BW^	82	125	11.9	11.6
1131	BCN//Doy1/Ae. tauschii (447)/3/Mayoor/TKSN1081/Ae. tauschii (222)	80	120	7.0	7.6
1139	Altar 84/Ae. tauschii (224)//2*Yaco/3/Mayoor/TKSN1081/Ae. tauschii (222)	80	120	7.1	7.3
1211	Opata/6/68.111/RGB-u/Ward/3/FGO/4/Rabi/5/Ae. tauschii (878)/7/MayoorBW/TKSN1081/Ae. tauschii (222)	82	120	7.8	7.2
1227	BCN//Doy1/Ae. tauschii (447)/3/Altar 84/Ae. tauschii (224)//2*Yaco	80	105	6.4	5.3
1232	BCN//Doy1/Ae. tauschii (447)/7/Opata/6/68.111/RGB-u//Ward/3/FGO/4/Rabi	80	100	6.8	5.4
1272	Mayoor/5/CS/Th. curvifolium//GlenÝ/3/ALD/PVN/4/CS/L. racemosus//2*CS/3/CNO79/6/Altar 84	85	115	7.0	6.2
1299	BCN//Ceta/Ae. tauschii (895)/3//Altar 84/Ae. tauschii (224)//2*Yaco	80	105	6.8	7.5
1315	BCN//Ceta/Ae. tauschii (895)/3//Altar 84/Ae. tauschii (224)//2*Yaco	80	100	6.5	6.3

D-genome contribution to Fusarium type-II resistance in synthetic-hexaploid wheats (SH; 2n = 6x = 42, AABBDD). [p. 94-97]

A. Mujeeb-Kazi and R. Delgado.

Our wide crosses program has given FHB (type II, spread) screening in Toluca, Mexico, a high priority since 1998. Two germ plasm categories have been candidates for evaluation that are broadly classified under interspecific and intergeneric hybridization areas. Within these two categories, the initial emphasis was placed on interspecific hybrids with the focus on contributions of Ae. tauschii accessions towards wheat improvement. The diversity in this species was exploited by hybridizing the diploid grass with elite durum wheat cultivars, which yielded SH wheats. Over 800 such synthetics have been produced so far and comprise the germ plasm for various stress-constraint screening evaluations.

Evaluation for scab resistance involves several categories or types. Our wide-crosses program conducts type-II (spread) tests. Promising entries are identified and transferred to the main pathology program for retesting of type-II infection data and also for extending the tests for other scab categories (types I, III, and IV). During these independent tests, we also monitor the type-II data generated, and when matches are observed, data is consolidated and reported (Table 3).

From the several SH wheats produced and tested, the first-year evaluation allowed us to select 36 entries with high resistance levels for type-II resistance based upon their similarity to Sumai 3 or their superiority to this resistant check cultivar. These 36 SH wheats were then evaluated between 1998 and 2001. Of these lines, entries with consistently better data than Sumai 3 for type-II resistance are presented in Table 3. A very high level of stringency testing was maintained over each cropping cycle in Toluca, Mexico, in that 10 fully extruded spikes from each SH entry were inoculated when the anthers became visible in the central spike region. Cotton swabs soaked in the inoculum were placed within the lemma and palea of the central floret of each spike under field conditions, covered with a glassine bag, and evaluated after 35 days for symptom development. The spore concentration was about 50,000. The data in Table 3 reports the mean percentage of infected florets for each SH entry across years. Susceptible and resistant check cultivar spikes also were inoculated daily. Emphasis was given to each individual spike within the 10 of each test entry. If a single spike within the 10 tested for an entry exceeded the 15 % type infection level (considered as the resistant score from the performance of Sumai 3 over several years of data) the entry was classified as susceptible. Additional stringency was provided by using the same three personnel to inoculate the entire wide-cross material tested. The SH subset reported here was handled by the same person each year (R. Delgado).

Each of the 15 SH wheats identified as resistant have a unique Ae. tauschii accession in the pedigree. The SH wheats are generally later flowering than elite bread wheats, later in maturity, taller, and exhibit a spring to mild facultative habit. The 1,000-kernel weight in a majority exceeds that of bread wheat (approximately 40 g) with a range from 47.7-62.4 g. Furthermore, most of these SHs with type-II resistance over 3 years of testing also have superior Karnal bunt resistance, where a similar long-term test across years in Obregon, Mexico, under artificial inoculation identified several entries with immunity to the pathogen (Table 3). This new batch of 15 synthetic hexaploid entries now forms the new base for current prebreeding activities that involve elite, but scab-susceptible, bread wheat cultivars as recipient parents.

New, free-threshing, bread wheat/D genome synthetic hexaploid derivatives with Septoria tritici resistance. [p. 96-98]

A. Mujeeb-Kazi and R. Delgado.

Synthetic hexaploids derived from durum wheat/Ae. tauschii crosses have become a potent source of diverse resistance/tolerance to biotic/abiotic stresses. Several such synthetics were identified with superior resistance to leaf blotch. The resistance has been attributed to at least two phenomenon (a) an extended latency period and (b) a lack of pycnidia formation. After identifying resistance in the synthetics, the traits are transferred into elite but S. tritici-susceptible bread wheat cultivars. This effort requires first the transfer, followed by selection of derivatives with a good agronomic-plant type that are free threshing in habit and preferably resistant to leaf, stem, and yellow rusts.

Ten bread wheat/Ae. tauschii//bread wheat advanced derivatives that were S. tritici-resistant and free-threshing were registered previously (Mujeeb-Kazi et al. 2001) and eight more subsequently identified (Delgado and Mujeeb-Kazi 2001) in a preliminary screening evaluation. We currently report on seven, new advanced lines and include more supportive data on the eight lines from screening in the year 2001 (Table 4). These 15 lines represent new genetic diversity contributed by several Ae. tauschii accessions for resistance to S. tritici and agronomic contributions of the durum and elite wheat cultivars in each resistant lines pedigree. The progressive, double-digit scoring scale (Eyal et al. 1987) used limited all selected lines to a stringent 3-2 score (Table 4) versus the susceptible bread wheat controls that reached levels of 8-7 to 9-9 at maturity.

All the 15 lines are homozygous through the use of a wheat/maize haploidy induction protocol (Mujeeb-Kazi 2000). These double haploids are current candidates for germ plasm registration after seed increase.

References.

• Delgado R and Mujeeb-Kazi A. 2001. Septoria resistance in synthetic hexaploids and their advanced derivatives from bread wheat crosses. Ann Wheat Newslet 47:109-111.
• Eyal Z, Scharen AL, Prescott JM, and van Ginkel M. 1987. The Septoria diseases of wheat: Concepts and methods of disease management. CIMMYT, Mexico, D.F. pp. 1-46.
• Mujeeb-Kazi A. 2000. An analysis of the use of haploidy in wheat improvement. In: Application of biotechnologies to wheat breeding (Kohli MM and Francis M eds). La Estanzuela, Uruguay, 19­20 November, 1998. p. 33-48.
• Mujeeb-Kazi A, Cano S, Rosas V, Cortés A, and Delgado R. 2001. Registration of five synthetic hexaploid wheat and seven bread wheat germplasm lines resistant to wheat spot blotch. Crop Sci 41:1653-1654.

Haploidy in bread wheat: the current protocol. [p. 97-99]

A. Mujeeb-Kazi, S. Cano, A.A. Vahidy, T. Razzaki, J.L. Diaz-de-León, and R. Delgado.

Haploid production in bread wheat using the sexual, bread wheat/maize procedure has developed into an efficient tool that is addressing several research areas (Mujeeb-Kazi 2000). Most significant, is the use in wheat breeding as the protocol enhances the work/cost efficiency associated with eventual varietal release. Other applications cover genetics, cytogenetics, molecular biology, pathology, and transformant stability. A global price per doubled haploid (DH) production ranges from approximately USD $5-60, with a majority of cost between UDS $ 25-40. Our costs are USD $10 during the normal cycle for spring habit wheats (June to October) or USD $ 15 at other times for spring wheats plus winter/facultative. We describe below our current DH protocol stages after summarizing data of a decades of investigation across a range of bread wheat-based materials of various habits. We contend that if our program only focused on DH production, the service, if performed in Mexico with its well-established infrastructure in El Batan, CIMMYT, Int., would be UDS $5/DH for spring wheats and USD $7.50 for winter/facultative germ plasm during the normal June to October cycle.

The protocol steps are as follows The experimental details of methodology are now fine tuned since our report in the Annual Wheat Newsletter (47:116, 2001) and are highlighted here for facilitating ready access.

1.	Cut spikes from selected plants and keep in tap water in plastic jars under greenhouse regimes of 24 C day/14 C night, 65 % RH, and 14-h natural light.
2.	Hand emasculate each spike 2 days after cutting according to the conventional breeding procedure. Cover with a plastic bag holding about 15 spikes to promote humidity.
3.	Pollinate with fresh maize pollen (9:30-10:30 a.m.) 3 days after emasculation. Spikes are left uncovered after pollination. 2,4 dichlorophenoxy-acetic acid, at 100 ppm, is added to each plastic container.
4.	Treat with 2, 4 dichlorophenoxy-acetic acid for 3 days (a variation from 6 days used earlier). The reduced duration time promotes speedier germination of embryos in the media.
5.	Culture media, seedling differentiation, transplanting, colchicine treatment ,and management aspects are all similar to those reported earlier (Mujeeb-Kazi 2001).

The data from close to 7,000 DHs produced between June 2001 and March 2002 suggest an embryo-recovery frequency of 25-35 %, differentiation into seedlings between 90-100 %, and a doubling rate between 95-100 %. Some researchers have achieved an embryo-recovery frequency between 50-70 %, but the final DH output is low because of lower rates for differentiation and doubling. We are exploring if the use of gibberellic acid (75 ppm) in the crossing stage and the early (bud) pollinations used earlier in complex intergeneric hybridizations (Mujeeb-Kazi et al. 1987) can augment our present 25-35 % embryo-recovery rate. Currently, this sexual haploid induction route is a favorite tool for bread wheat germ plasm. The promise of the newer microspore technology is an upcoming alternative that will revolutionize the working scenario if genotype specificity does not exist. This development is keenly awaited in the public sector.

References.

• Mujeeb-Kazi A. 2000. An analysis of the use of haploidy in wheat improvement. In: Application of biotechnologies to wheat breeding (Kohli MM and Francis M eds). La Estanzuela, Uruguay. 19-20 November, 1998. pp. 33-48.
• Mujeeb-Kazi A. 2001. Intergeneric hybrids in wheat: Current status. In: Proc IV Internat Triticeae Symp (Hernandez P, Moreno MT, Cubero JI, and Martin A eds). 10-12 September 2001, Córdoba, Spain. pp. 261-164.
• Mujeeb-Kazi A, Roldan S, Suh DY, Sitch LA, and Farooq S. 1987. Production and cytogenetic analysis of hybrids between Triticum aestivum and some caespitose Agropyron species. Genome 29:537-553.
  

Disomic chromosome additions of Thinopyrum elongatum (2n = 2x = 14) in bread and durum wheat. [p. 99-100]

A. Mujeeb-Kazi, A. Cortés, V. Rosas, J.L. Diaz-de-León, A.A. Vahidy, and T. Razzaki.

Thinopyrum elongatum is a grass noted for its tolerance to salinity and resistance to FHB, two constraints that limit bread and durum wheat production. The species was hybridized with the bread wheat cultivar Chinese Spring (Dvorak and Knott 1974) that subsequently led to production of addition lines. Dvorak et al. (1988) reported homoeologous additions of chromosomes belonging to groups 3, 4, and 7 as being positive contributors to salt tolerance. We decided to remake this hybrid combination with two significant modifications. First, Th. elongatum was used as the female parent in the hybrid in order to capture the cytoplasmic influence if any should exist and, second, use a commercial bread wheat cultivar other than Chinese Spring so the derivatives would be agronomically superior and better adapted to global field testing conditions.

Consequently, a hybrid between Th. elongatum and the T. aestivum cultivar Goshawk 'S' was made and its amphiploid (2n = 8x = 56, AABBDDEE) produced. One strategy was to screen the amphiploid for salt tolerance and resistance to FHB (type II). If the observations were positive for either stress, the seven possible Th. elongatum chromosome addition lines would be produced. The amphiploid was tolerant/resistant to both stresses (Mujeeb-Kazi 2001), and by adopting an F1 topcross breeding protocol, we have produced the seven disomic, chromosome addition lines in the topcross bread wheat cultivar Prinia, which is superior to Goshawk. The C-banded karyotype of Th. elongatum (Fig. 1) was used to validate the addition lines because each alien chromosome had a unique banding pattern and the bread wheat chromosomes. The addition lines are highly fertile and are the basis for delineating their associations with both stress constraints being investigated. We expect that more than one chromosome will contribute to the resistance to each stress. The ph-gene-mediated protocol (Mujeeb-Kazi 2001) has already been set in place.

For durum wheats, salinity tolerance is of some concern but the lack of scab resistance currently is of greater significance. The contributions of alien species for durum wheat improvement are not too extensive and based on the response of Th. elongatum in a bread wheat background for superior type-II scab resistance, we initiated crosses between this diploid (pollen parent) and an elite durum cultivar. An amphiploid was produced (2n = 6x = 42, AABBEE) from the F1 hybrid (2n = 3x = 21, ABE) that gave a promising type-II scab resistance score. Using a conventional topcross breeding strategy, we have produced single to multiple monosomic additions. Jauhar and Peterson (2000) observed difficulty in stabilizing Th. elongatum additions in durum wheat and, as a result, the successful transfer of scab resistance to yield a stable resistant euploid (2n = 4x = 28) durum from any of the Th. elongatum chromosomes contributing to scab resistance has not been achieved. Our strategy, in addition to selfing the single/multiple monosomic additions to extract various disomics with 2n = 4x = 28 plus a unique Th. elongatum chromosome pair from the selfed progeny, has been to use those durum cultivars in the top cross and in the original hybrid cross that respond to haploid generation via the maize procedure. Consequently, we produced a large number of unique monosomic Th. elongatum additions with n = 2x = 14 plus one alien chromosome, where each of the seven Th. elongatum chromosomes were represented. These haploids have been treated with colchicine and have set seed. The harvest and cytological confirmation, coupled with seed increase of the 2n = 4x = 28 + 2, covering all unique Th. elongatum chromosome pairs is now close at hand.

This study was targeted towards the production of the complete set of Th. elongatum disomic addition lines in an elite spring durum wheat cultivar. The next step will be scab screening in Toluca, Mexico. Based upon our observations with Th. bessarabicum, scab resistance may be present on several of the Th. elongatum addition lines. As a precautionary step, we already have crossed the durum/Th. elongatum amphiploid with the durum ph1c genetic stock to enforce homoeologous exchanges that have been described by Mujeeb-Kazi (2001) for the bread wheat germ plasm. This approach also should address the salinity tolerance objective where several Th. elongatum chromosomes are known to be contributors.

Reference.

• Dvorak J and Knott DR. 1974. Disomic and ditelosomic additions of diploid Agropyron elongatum chromosomes to Triticum aestivum. Can J Genet Cytol 16:399-417.
• Dvorak J, Edge M, and Ross K. 1988. On the evolution of the adaptation of Lophopyrum elongatum to growth in saline environments. Proc Natl Acad Sci USA 85:3805-3809.
• Jauhar PP and Peterson TS. 2000. Towards transferring scab resistance from a diploid wild grass, Lophopyrum elongatum, into durum wheat. In: 2000 Natl Fusarium Head Blight Forum, Erlanger, KY, 10-12 December. pp. 201-204.
• Mujeeb-Kazi A. 2001. Intergeneric hybrids in wheat: current status. In: Proc IV Internat Triticeae Symp (Hernandez P, Moreno MT, Cubero JI, and Martin A eds). 10-12 September 2001, Córdoba, Spain. pp. 261-164.

A complete set of Thinopyrum bessarabicum disomic chromosome addition lines in the bread wheat cultivar Prinia. [p. 100-101]

A. Mujeeb-Kazi, A. Cortés, A.A. Vahidy, T. Razzaki, J.L. Diaz-de-León, and R. Delgado.

Thinopyrum bessarabicum is a self-fertile, maritime grass species possessing salt tolerance (Gorham et al. 1985), root-knot nematode resistance (Jensen and Griffin 1994), and resistance to FHB (Mujeeb-Kazi 2001). Currently in our wide cross program, breeding for resistance to FHB is of high priority for bread wheat. One utilization strategy is to produce alien chromosome addition lines in bread wheat, screen these for stress resistance, and cytogenetically manipulate to them to introgress the beneficial alien contribution from the target disomic addition lines. Our initial step was to produce a complete addition line set of the seven disomic Th. bessarabicum chromosomes. Six disomic additions were initially reported by Mujeeb-Kazi et al. 2000 (1J, 2J, 3J, 4J, 5J, and 7J). These lines subsequently were analyzed by FISH and AFLP diagnostics (Zhang et al. 2002) and the status of five (1J, 2J, 4J, 5J, and 7J) were confirmed. Line 3J was not a disomic addition but a translocation product. Thus, additions for 3J and 6J were missing that we have now produced from a BC1, self-fertile, 50-chromosome derivative possessing 21 bivalents of wheat and four Th. bessarabicum bivalent chromosomes including the 3J and 6J pairs.

Backcross derivatives of the 50-chromosome BC1 plant with the cultivar Prinia gave 46-chromosome progeny; 42 wheat plus four of Th. bessarabicum. An additional backcross gave progeny that was either a 3J or a 6J single monosomic (43 chromosomes) or was a double 3J + 6J monosomic (44 chromosomes). Each of these derivatives were crossed with maize to yield 22-chromosome haploids, which were validated by C-banding as 21 + 3J and 21 + 6J and treated with colchicine to yield the respective 3J and 6J disomic addition lines. Thus, the disomic set of the seven Th. bessarabicum chromosomes was completed. Interdisomic addition line crosses were made involving each disomic addition line (i.e., 1J/2J, 1J/3J, 1J/4J, 1J/5J, 1J/6J, 1J/7J). The F1 progeny was cytologically analyzed by chromosome counts (2n + 6x = 42 + 2), Giemsa C-banding, and meiotic metaphase association, where 21 II+2 I indicated the validity of each addition line. Each addition line also was checked by FISH and C-banding (mitosis) to ascertain structural integrity. All seven addition lines are in a spring bread wheat cultivar Prinia background (93.75 %) and have good fertility. These lines will be more suitable for biotic/abiotic stress screening because of their superior agronomical background. The karyotype in Fig. 2a is for the seven alien Th. bessarabicum chromosomes that are associated with disomic addition lines 1J to 7J. These lines are partially characterized by their respective biochemical markers (William and Mujeeb-Kazi 1995). Each disomic addition line has a stable meiotic association with 22 bivalents (Fig. 2b) and normal anaphase I separation (Fig. 2c) with high seed set.

References.

• Gorham J, McDonnel E, Budrewicz E, and Jones RG. 1985. Salt tolerance in the Triticeae: growth and solute accumulation in leaves of Thinopyrum bessarabicum. J Exp Bot 36:1021 1031.
• Jensen K and Griffin GD. 1994. Resistance of diploid Triticeae species and accessions to the Columbia root-knot nematode, Meloidogyne chitwoodi. J Nematol 26:635-639.
• Cortés A, Rosas V, Cano S, Delgado R, Zhang J, Li X, Wang RC, and Mujeeb-Kazi A. 2000. Thinopyrum bessarabicum (2n = 2x = 14, JJ) disomic chromosome addition lines in bread wheat: current germ plasm status. Ann Wheat Newslet 46:74-75.
• Mujeeb-Kazi A. 2001. Intergeneric Hybrids in Wheat: current status. In: Proc IV Internat Triticeae Symp (Hernandez P, Moreno MT, Cubero JI, and Martin A eds). 10­12 September 2001, Córdoba, Spain. pp. 261-164.
• William MDHM and Mujeeb-Kazi A. 1995. Biochemical and molecular diagnostics of Thinopyrum bessarabicum chromosomes in Triticum aestivum germ plasm. Theor Appl Genet 90:952-956.

Origin and cytogenetics of a bread wheat/Aegilops ovata intergeneric hybrid and its complete/partial amphiploids. [p. 102-103]

A.A. Vahidy, F. Shafiq, A. Cortés, V. Rosas, and A. Mujeeb-Kazi.

The wild wheat relatives of the tribe Triticeae are distributed in three gene pools; primary, secondary, and tertiary. Utilization of these pools (other than conventional) forms the area of wide hybridization that includes both interspecific and intergeneric hybridization. In general, wide hybridization has become an important tool for widening the genetic variability of cultivated species. It has been particularly useful in transferring desirable genes into cultivated wheat from their wild relatives for addressing biotic and abiotic stress constraints. These wild species represent a valuable source of genetic variability for wheat breeding, with Aegilops species being a rich source of desirable genes for wheat improvement. In such alien-diversity introgression programs, the production of F1 hybrids is a critical starting point from which advanced derivatives are developed. The use of the alien source is an important factor and in general the primary genepool species have priority since homologous exchanges facilitate rapid end-products to emerge. However, more distant sources residing in the tertiary gene pool also can provide superior resistance and do have a significant place in wide-crossing programs targeted for wheat improvement. Products from the use of these distant species are slow to obtain and often require complex cytogenetic manipulation strategies, but their exploitation is justified when one gauges the need for diverse genes that can add to durable stress resistances.

Aegilops geniculata is one such tertiary gene pool species that has superb resistance to Karnal bunt, BYDV, leaf rust, and cereal cyst nematode, coupled with a high level of salinity tolerance in a majority of its accessions. Of these, our major wheat production constraints in Pakistan are for Karnal bunt, leaf rust, and salinity, for which any possible introgressions into the lead cultivars of our region form a viable research objective. We decided to hybridize bread wheat cultivar Sarsabz with an Ae. geniculata accession and have developed some stable genetic stocks from this F1 hybrid that will form the basis of additional introgression studies. Intergeneric hybrids and addition lines were produced earlier and reported upon by Friebe et al. (1999) who produced 13 disomic addition and one monosomic addition lines, thus getting the complete set of 14 additions. This is the first time that such an attempt has been made in an elite wheat cultivar from Pakistan.

The F1 hybrid plants obtained from crossing Sarsabz with Ae. geniculata were all mitotically regular with 2n = 5x = 35, ABDUM chromosomes, and expressed a mean meiotic association of 30.3 univalents plus 2.32 rod bivalents. It was a low frequency cross. F1 management and colchicine treatment protocols were similar to those described by Mujeeb-Kazi et al. (1987). Three amphiploid seed were obtained; each with 2n = 10x = 70, AABBDDUUMM chromosomes, which were ascertained by orcein-stained, root-tip chromosome counts and Giemsa C-banding. The mean meiotic association of the amphiploid waw 4.6 univalents + 18.7 ring bivalents + 10.8 rod bivalents (total 29.5 bivalents) + 1.4 trivalents + 0.2 quadrivalents. The C1 progeny from these 70-chromosome amphiploids was highly aneuploid and less than 1.0 % of the plants possessed the expected normal chromosome number. However, there was an abundance of C1 progeny with 56 chromosomes. These plants were designated as partial amphiploids. Ganeva et al. (1992) also had observed similar aneuploid trends in the original amphiploid and chromosome number reductions. These partial amphiploids were highly fertile and produced derivatives from C2 to C6 that maintained 56 chromosomes (Fig. 3a). The expectation was that all the 42 wheat chromosomes would be present and 14 (A to N) would represent the contributions from Ae. geniculata; U, M, or a mixture of U- and M-genome chromosomes.

The partial amphiploid has remained stable over six generations of selfing and maintains the 56 mitotic chromosomes that are meiotically associated as 28 bivalents either as perfect rings or a mixture of rods and rings (Figs. 3b and 3c). The chromosome complement, however, deviates from the expected 42 chromosomes of wheat and 14 of Ae. geniculata because Giemsa C-banding identified 30 wheat and 26 Ae. geniculata chromosomes. The missing wheat chromosomes were 3A, 4A, 1B, 2D, 5D, and 7D (six pairs), and the Ae. geniculata chromosomes present were representative of 13 pairs and given arbitrary designations of A to M with N assigned to the missing pair. The BC1 progeny from this amphiploid with Sarsabz gave stable plants with 49 chromosomes and all 13 Ae. geniculata chromosomes in the amphiploid were represented in a single dose. Thus, it would be possible to develop 13 disomic chromosome addition lines (A to M), and the missing line would be for chromosome N. The meiosis of the BC1 plant had a majority of the meiocytes with 15 bivalents (all of wheat) + 19 univalents that were composed of 13 Ae. geniculata (A to M) and six wheat (3A, 4A, 1B, 2D, 5D, and 7D) chromosomes. Subsequent backcrossing of these 49-chromosome BC1 plants has led to the production of several derivatives where euploidy for the 42 chromosomes of wheat has been achieved and single to triple monosomic addition chromosomes are present. Upon selfing, these lines have led to the isolation of 44-chromosome progeny in which a disomic Ae. geniculata chromosome pair is present. The additions completed so far are for 11 chromosomes alphabetically designated as A, B, D, E, F, G, H, I, J, L, and M. Addition lines of two of the Ae. geniculata chromosomes are not available and additional backcross progenies are needed for the isolation of these chromosomes designated as C and K. To speed up this process, we have generated haploid plants from each target BC derivative that represent the missing chromosomes C and K in the population. The selfed progeny also will be used to complement this haploid strategy. If the two missing chromosome addition lines are not produced, then the selfed germ plasm of the specific backcross will lead to another round of haploid generation and selfing.

The hybridization of Ae. geniculata with the elite wheat Sarsabz coupled with additional backcrosses to the same cultivar has enabled us to produce derivatives in a superior wheat plant type that will facilitate testing of these genetic stocks for the necessary stress constraints being addressed. We have modified the cytogenetic manipulation strategy of Mujeeb-Kazi (2001) slightly in that the use of the ph Chinese Spring genetic stock will be incorporated only on each of those 44-chromosome disomic addition lines that indicate a positive value. The progeny derived from this ph-manipulation strategy will be critically analyzed for wheat/alien exchanges.

References.

• Friebe B, Tuleen NA, and Gill BS. 1999. Development and identification of a complete set of Triticum aestivum-Aegilops geniculata chromosome addition lines. Genome 42:374-380.
• Ganeva G, Bochev B, and Veneva L. 1992. A new Triticum aestivum L. x Aegilops ovata L. amphiploid. Cereal Res Commun 20:183-192.
• Mujeeb-Kazi A, Roldan S, Suh DY, Sitch LA, and Farooq S. 1987. Production and cytogenetic analysis of hybrids between Triticum aestivum and some caespitose Agropyron species. Genome 29:537-553.
• Mujeeb-Kazi A. 2001. Intergeneric Hybrids in Wheat: current status. In: Proc IV Internat Triticeae Symp (Hernandez P, Moreno MT, Cubero JI, and Martin A eds). 10-12 September 2001, Córdoba, Spain. pp. 261-164.

Scab resistance of some partial amphiploid derivatives of bread wheat/Thinopyrum intermedium. [p. 104]

Sun Lianfa, Zhang Jumei, Song Qingjie, and Zhang Yanbin (Crop Breeding Institute of Heilongjiang Academy of Agricultural Sciences, 368 # Xuefu Road, Harbin, Neimjiang, P.R. of China, 150086), and Lucy Gilchrist and Abdul Mujeeb-Kazi.

The Crop Breeding Institute of Heilongjiang Academy of Agricultural Sciences has been engaged in a bread wheat/Th. intermedium crossing program since the 1970s. Partial amphiploids were developed by backcross breeding and named Yuanzhong 1, Yuanzhong 2, Yuanzhong 3, Yuanzhong 4, Yuanzhong 5, Yuanzhong 6, and Yuanzhong 7 (syn. Zhong 1 to 7). These lines are known to possess resistance or tolerance to various biotic and abiotic stresses and are widely used as important germ plasm for wheat improvement. In Heilongjiang, the Academy of Agricultural Sciences developed three wheat varieties called Longmai 8, 9 and 10; the Northeast Normal University in Jilin province released Xiaobing 32 and 33 derived from Yuanzhong 1 and 3; and the Shannxi Academy of Agricultural Sciences obtained Shanmai 89150, 897, and 611 derived from Yuanzhong 4 and 5. Some of the parental partial amphiploid lines also have been used in Australia for BYDV resistance.

Cumulative results from the use of the Yuangzhon partial amphiploids indicate that these germ plasm lines are highly resistant to leaf rust, stem rust, stripe rust, spot blotch, powdery mildew, WSMV (except Yuanzhong 1), take-all (except Yangzhong 1), and BYDV. In 2001, these materials were inoculated with the FHB pathogen to evaluate type-II resistance in Heilongjiang, China. At CIMMYT, we examined their DON content (type III) using the FLUOROQUANT method and determined their somatic chromosome number. These results are listed in Table 5.

The data in Table 5 shows the mitotic chromosome number and range, the number of infected spikelets/spike, the percent of infected spikelets, and the DON content of the partial amphiploids. Yuanzhong 2 and 5 have the lowest values among the tested materials. Both these partial amphiploids could be potential and valuable resistant germ plasm for incorporating scab resistance into bread wheat. The data of Table 5 are from one cycle of tests and additional testing is necessary. This testing is planned for a field study in China and laboratory studies at CIMMYT, Mexico, during 2002.

Currently, we conclude that Yuanzhong 2 and 5, show satisfactory type-I and type-II resistance to FHB. Yuanzhong 6 and Yuanzhong 7 are from the same cross as Yuanzhong 5 and are similar to Yuanzhong 5 for many characteristics. Thus, these two (6 and 7) were not evaluated for scab resistance in this study. Both of the resistant partial amphiploids (2 and 5) have 56 chromosomes with normal bivalent meiosis indicative of stability. The stability is reflected in the BC1 progeny, which have a normal 49 chromosomes. We are using two strategies of resistance introgression. The conventional strategy relates to the production of disomic addition lines, screening, and the cytogenetic manipulation of the resistant entry to permit genetic introgression. The second option uses is ph-gene mediated at the 56-chromosome level and also later when the addition line/s with scab resistance have been identified. The delayed involvement of the ph gene holds priority as this route will be more targeted. The protocol being utilized for the ph-based manipulation is that of Mujeeb- Kazi (2001).

Reference.

• Mujeeb-Kazi A. 2001. Intergeneric Hybrids in Wheat: current status. In: Proc IV Internat Triticeae Symp (Hernandez P, Moreno MT, Cubero JI, and Martin A eds). 10-12 September 2001, Córdoba, Spain. pp. 261-164.

Cytogenetics of wheat and alien Triticeae species amphiploids. [p. 105-108]

A. Cortés, A.A. Vahidy, T. Razzaki, V. Rosas, R. Delgado, and A. Mujeeb-Kazi.

Intergeneric hybrids within the Triticeae are a potent source of exploiting alien genetic diversity for wheat improvement. Perennial sources yield perennial hybrids that can be maintained as a living herbarium only requiring meticulous maintenance via cloning each combination twice a year with a cytological check to ensure their valid hybrid status. Hybrids with the annual Triticeae species tend to be annual and producing an amphiploid is necessary for their maintenance. The other option is to pollinate the self-sterile F1 with a wheat cultivar to generate a BC1 progeny, utilizing the fusion of an unreduced egg-cell with the pollen gamete. Our technique has been very productive for yielding doubled products in the maize-induced, DH program where over the past several years the doubling frequency has ranged between 90.0-100.0 % across many bread wheat germ plasms. However, amphiploid production using colchicine and dimethylsulfoxide (DMSO) for intergeneric hybrids been an extremely low frequency event for us over a span of two decades and has never exceeded more than 5.0 % at any one time; generally being less than 1.0 %. Despite the low doubling rate with intergeneric hybrids, we have been able to produce a large number of amphiploids (Table 6 and Table 7) and still continue to expand the list by varying the colchicine concentration and treatment times from those reported by Mujeeb-Kazi et al. (1987). The significance of amphiploids was emphasized by Gill (1987), and the importance of such genetic stocks since then is even further recognized.

Rosas et al. (1996) reported on the pedigree, expected C0 chromosome and plant number, the generations of advance of each amphiploid, total amphiploid plants observed in each combination, the mitotic chromosome range, and seed amount available. We are now updating the salient aspects for these and other amphiploid combinations. The meiotic association data for all aneuploid combinations also is in our database. Indications (*) also are provided that may allow researchers to target their programs around some combinations to address various biotic/abiotic stresses that constrain wheat production. In those cases, we have made an advances by top-crossing the desired amphiploids by a quality spring bread wheat and also by the Chinese Spring ph-mutant genetic stock for the swift incorporation of these materials in wheat developmental programs as required by collaborators globally. The use of the ph stock follows the strategy that Mujeeb-Kazi (2001) proposed for facilitating the production of wheat/alien chromosome translocation products. Amphiploids with a durum base also have been exploited similarly by crossing the combinations with an elite, durum, spring wheat cultivar and selecting a few combinations by the durum ph1c genetic stock.

In general, hybrids that have given us fertile amphiploids (Table 6 and Table 7) have wheat as the female parent with the alien male donors ranging from diploid (2n = 2x = 14 ) to hexaploid (2n = 6x = 42). The resulting amphiploids thus range from 2n = 8x = 56 to 2n = 12x = 84 for bread wheat and from 2x = 6x = 42 to 2n = 10x = 70 for durum wheat. Hyper- and hypoploidy existed in all of the combinations but greater mitotic stability was prevalent in those combinations where the amphiploid chromosome number was either 42 or 56. These germ plasms also were high in fertility and produced sufficient plump seed in larger numbers per plant than the rest of the amphiploids with 70 to 84 chromosomes.

Cytological analyses of the various amphiploids over several (Cn) generations have indicated that even when the starting plant has a stable chromosome number, it rarely produces progeny that maintains this stability particularly when the amphiploid is of 70 or 84 chromosomes. The progenies of amphiploids with 42 or 56 chromosomes are comparatively more stable and very few derivatives are aneuploid. We have maintained one sample from three individual plants of each amphiploid that have the normal chromosome number or very near the expected number. In addition, for each amphiploid, there is a bulk sample from several other plants that had some aneuploidy. These comprise the initial sources for stress screening and, if a combination is identified as being of positive value for a trait, then a stable individual plant sample can be utilized for prebreeding via addition line production or by ph-based chromosome manipulation.

Stresses of greater current significance for wheat production in the various global megaenvironments are related to biotic and abiotic areas. Some of these are the resistance to the three rusts, FHB, Cochiobolus sativus; Karnal bunt, S. tritici, S. nodorum, powdery mildew, BYDV, cereal cyst nematode, general root rots, RWA; tolerance to salinity, drought, heat, cold, sprouting, waterlogging, aluminum, micronutrients; and yield. All stress constraints are influenced by quality. For sustainable agriculture, a blend of genes representing maximized genetic diversity is advantageous and in this context, and the role of the amphiploid stocks reported here becomes highly significant. The practical value of these amphiploids is genetically assured because their F1 hybrids all exhibited a codominant phenotype and so do their respective amphiploids. We infer the codominance as an indicator of the genetic expression of the alien species in a bread or durum wheat background. From the total F1 hybrids that we have produced, several still have not responded to doubling and still remain candidates of a continuously on-going exercise that is carried out twice a year after each physical cloning of the F1s. In addition, a program to further enrich the genetic pool targets producing new hybrid combinations since several annual and perennial Triticeae species have still not been hybridized with wheat.

References.

• Gill BS. 1989. The use of chromosome banding and in situ hybridization for the study of alien introgression in plant breeding. In: Review of Advances in Plant Biotechnology 1985-88, 2nd Internat Symp Genetic Manipulation in Crops (Mujeeb-Kazi A and Sitch LA eds). CIMMYT, Mexico, D.F. Mexico and IRRI, Manila, the Philippines.
• Mujeeb-Kazi A, Roldan S, Suh DY, Sitch LA, and Farooq S. 1987. Production and cytogenetic analysis of hybrids between Triticum aestivum and some caespitose Agropyron species. Genome 29:537-553.
• Mujeeb-Kazi A. 2001. Intergeneric Hybrids in Wheat: current status. In: Proc IV Internat Triticeae Symp (Hernandez P, Moreno MT, Cubero JI, and Martin A eds). 10-12 September 2001, Córdoba, Spain. pp. 261-164.
• Rosas V, Delgado R, Cortés A, and Mujeeb-Kazi A. 1996. Cytogenetics of some amphiploids involving Triticum turgidum and T. aestivum cultivars with alien Triticeae species. Annual Wheat Newslet 42:145-146.
  

Identification of specific Aegilops geniculata microsatellite markers potentially useful for detecting introgressions into bread wheat. [p. 108-110]

M. Zaharieva, K. Suenaga (Japan International Research Center for Agricultural Sciences, 1-1, Ohwashi, Tsukuba, Ibaraki 305-8686), M. William, and A. Mujeeb-Kazi.

Aegilops geniculata is a valuable source of genes for improving wheat resistance to some biotic and abiotic stresses. Promising Ae. geniculata accessions with resistance to BYDV and CCN were selected and crossed with susceptible, high-yielding bread and durum wheat cultivars and the Chinese Spring ph-mutant line using conventional protocols (Mujeeb-Kazi et al. 1987).

For each cross, some F1 hybrids were treated with colchicine to produce amphiploids. The remaining F1 hybrids were backcrossed to their wheat parents to produce BC1 derivatives. The BC1 plants with complete chromosome set (2n = 8x = 42, AABBMU) were crossed with bread or durum wheat parents (BC2) or selfed to produce a BC1F2. This seed will be used to advance desired combinations for applied purposes via addition, substitution, and recombination lines.

To facilitate the identification of the introgressed alien material in a wheat background, we made a search for Ae. geniculata M- and U-genome-specific molecular markers. Microsatellite SSRs, which show adequate levels of polymorphism and are known to be widely distributed in the cereal genome, have been used in a number of studies involving genotype identification, genetic diversity, mapping, and identification of marker-trait associations. We used a set of SSRs to analyze the chromosomal constitution in the progenies of Triticum/Ae. geniculata crosses, avoiding the conventional time-consuming, cytological analyses.

Ae. geniculata is presumed to be an amphiploid of two diploid species Ae. comosa (M genome) and Ae. umbellulata (U genome) (Kimber et al. 1988). Friebe et al. (1999) confirmed the chromosomes similarities between the U and M genomes of Ae. geniculata and the diploid progenitors, developed a complete set of T. aestivum/Ae. geniculata addition lines and assigned all Ae. geniculata U and M chromosomes to their homoeologous groups. Using C-banding, Fernandez-Calvin and Orellana (1992) analyzed the pairing affinities between Ae. geniculata and wheat genomes in an Ae. geniculata/T. aestivum hybrid with the ph1b mutation. They revealed that the A- and D-genome chromosomes more frequently associated with the M- and U-genome chromosomes of Ae. geniculata than did the wheat A or D or Ae. geniculata M or U chromosomes with wheat B-genome chromosomes.

Consequently, our priority was to study D-genome microsatellites derived from hexaploid wheat or Ae. tauschii. Wheat microsatellites mapped on A genome will be tested further in order to extend the possibility of detecting the alien material in potential A-U- and A-M-recombinations.

A set of 24 genotypes involving nine accessions of Ae. geniculata with resistance traits, three T. durum and three T. aestivum cultivars with high-yield potential but susceptible to diseases and pests, three Ae. comosa, three Ae. umbellulata, and three Triticum/Ae. geniculata hybrids were used in this study (Table 8). DNA extraction, PCR amplification, and gel electrophoresis were made according to standard established protocols of the CIMMYT Molecular Genetics Laboratory (Hoisington et al. 1994).

Sixty-six wheat and Ae. tauschii microsatellites (GWM and GDM), provided by M. Röder (IPK, Gatersleben, Germany), were tested (Table 9). All primer pairs used gave amplification products on hexaploid wheat. Among them, 53 (80.3 %) also amplified products on Ae. geniculata, the Triticum/Ae. geniculata hybrids, and at least one of the diploid species. Only five microsatellites revealed monomorphic bands between Triticum and Ae. geniculata genotypes. From the remaining 48 primers, 24 (50 %) showed useful polymorphisms (strong bands that easily detected size differences between Triticum and Ae. geniculata alleles) and could be employed as molecular markers for Ae. geniculata chromosomes. Eight of these clearly distinguished all T. durum and T. aestivum cultivars from all Ae. geniculata accessions tested (Table 9). The other 16 only differentiated T. durum from Ae. geniculata genotypes, only T. aestivum from Ae. geniculata genotypes, or only some specific Triticum/Aegilops combinations.

The eight selected microsatellites were mapped on chromosomes 1D (GWM848), 2D (WMG455, GDM35, and GDM148), 4D (GDM34), 5D (GWM205), and 7D (WMG974 and GDM37) (Röder et al. 1998, unpublished; Pestsova et al. 2000). They are good candidates for Ae. geniculata chromosome identification. These primers and those giving good differentiation between Ae. geniculata and T. durum or T. aestivum will be tested on a set of Chinese Spring nullisomic­tetrasomic lines and on the T. aestivum/Ae. geniculata chromosome addition lines (developed and described by Friebe et al. 1999) for assigning appropriate location of the detected loci. Once the chromosomal location of these markers is verified using cytogenetic stocks, they can be used to identify wheat lines with introgressions from Ae. geniculata.

References.

• Friebe BR, Tuleen NA, and Gill BS. 1999. Development and identification of a complete set of Triticum aestivum-Aegilops geniculata chromosome additional lines. Genome 42:374-380.
• Fernandez-Kalvin B and Orellana J. 1992. Relationships between pairing frequencies and genome affinity estimations in Aegilops ovata X Triticum aestivum hybrid plants. Heredity 68:165-172.
• Hoisington D, Khairallah M, and Gonzalez-de-Leon D. 1994. Laboratory protocols: CIMMYT Applied Molecular Biology Laboratory, 2nd Ed. CIMMYT, Mexico, D.F. Mexico.
• Kimber G, Sallee PJ, and Feiner MM. 1988. The interspecific and evolutionary relationships of Triticum ovatum. Genome 30:218-221.
• Mujeeb-Kazi A, Roldan S, Suh DY, Sitch LA, and Farooq S. 1987. Production and cytogenetic analysis of hybrids between Triticum aestivum and some caespitose Agropyron species. Genome 29:537-553.
• Pestsova E, Ganal MW, and Röder MS. 2000. Isolation and mapping of microsatellite markers specific for the D genome of bread wheat. Genome 43:689-697.
• Röder MS, Korzun V, Wendehake K, Plaschke J, Tixier MH, Leroy P, and Ganal MW. 1998. A microsatellite map of wheat. Genetics 149:2007-2023.
• Zaharieva M, Cortéz A, Rosas V, Cano S, Sanchez J, Juarez L, Delgado R, and Mujeeb-Kazi A. 2001. Potential of Aegilops geniculata genetic resources for wheat improvement. Ann Wheat Newslet 47:102-103.

Cytogenetics of wheat and alien Triticeae species self-fertile BC1 derivatives. [p. 110-111]

A. Cortés, V. Rosas, R. Delgado, and A. Mujeeb-Kazi.

Bread wheat cultivars when hybridized with alien Triticeae species yield perennial intergeneric hybrids that are generally of a normal cytogenetic make-up and possess half the chromosomes of each parent involved. The F1 hybrid may produce amphiploids when treated with colchicine. After emasculation and pollination by a bread wheat cultivar, these hybrids are the source of the BC1 progeny. When an amphiploid is not obtained, the self-sterile but female-fertile perennial F1 hybrid can be directly pollinated by bread wheat to yield BC1 progeny similar to that from the amphiploid route. This alternate route extends the range of alien diversity for agricultural utility. In either case, the BC1 germ plasm can be screened for resistance to biotic/abiotic stresses.

A unique advantage of almost all the BC1s we have produced is their self-fertility and codominance of the expressed phenotype (Table 10). All bread wheat/hexaploid alien species F1 hybrids (2n = 6x = 42) yield BCI derivatives that are cytologically normal with 2n = 9x = 63 chromosomes. When grown and allowed to self, all are self-fertile except that the BC1F2 derivatives are either 2n = 9x = 63 or 2n = 8x = 56. In the latter case, a single genome is eliminated and the remaining two are closely related as evidenced by the predominant normal meiotic relationships of bivalent associations (Delgado et al. 1996).

Intergeneric hybrids with 2n = 5x = 35 chromosomes all lead to BC1 self-fertile and stable progeny of 2n = 8x = 56 chromosomes that pair as bivalents during meiosis. The 56-chromosome BC1 combinations are of great cytogenetic and applied interest. Continued selfing for seed increase enables recombination to occur and be perpetuated due to the bivalent associations of the 14 chromosomes of the two closely related alien genomes. Hence, one could expect the alien addition lines produced directly from the F1 hybrid and those from the BC1Fn material to be structurally different. In the F1 hybrid, the two related genomes (e.g. E1E2 designations for Th. curvifolium) do not pair, and so the structural entity is unaltered. In BC1F1 with 56 chromosomes, 28II are common, which indicates a E1- and E2-genomic association. This suggests structural modifications in the E1 and E2 chromosomes as a consequence of recombination, which could significantly alter the content of alien addition lines produced from such a BC1Fn source as compared to the minimally altered chromosome addition lines produced from the BC1F1 source where a single recombinational opportunity prevails. The practical advantage is that recombination may facilitate gene pyramiding. The scheme in Fig. 4 elucidates these crucial steps based upon a bread wheat and Th. curvifolium F1 hybrid combination.

Maintenance. For each combination in Table 10, BC1F2 selfed seed was obtained and 8-10 seed/entry were planted. These plants were cytologically analyzed and two plants for each combination with normal/near normal mitotic counts, vigorous growth, and near perfect bivalent meiosis were selected for further advance. From these two plants, those with the highest and plumpest seed were chosen as the BC1F3 candidate for a similar process to give a BC1F4 candidate. BC1F10 plants with normal or near normal cytology produced seed that was bulked to give the seed number (g) indicated in Table 10.

From each BC1F10 group of plants, one candidate plant also was selected and its progeny maintained as an individual plant source for further advance if needed and for critical study if the altered chromosomal structure by recombination within related genomes would warrant further investigation. Each such selected plant across each combination had a vigorous growth habit, was mitotically near normal or normal, had stable meiotic associations, and set abundant well-filled seed.

Reference.

• Delgado, R., A. Cortés, V. Rosas, and A. Mujeeb-Kazi. 1996. Triticum aestivum x perennial Triticeae BC1 self-fertile derivatives with complete and partial synthetic genomes. Ann Wheat Newslet 42:146-147.