SENSAKO
Stellenbosch Branch, P.O. Box 3079, 7602 Matieland, South Africa.
Doubled haploid research.
R. de V. Pienaar and Marizanne Horn.
During the period from March to November, 1996, 14,450
spring wheat florets (of eight genotypes) were emasculated and
pollinated (when the most mature florets of the spikes began to
open) with F4 derivatives of Seneca 60 maize. Twenty-four
hours later, the florets were filled with the best wheat haploidizers
(WHs) identified in the previous 4 years and covered with brown
paper bags. Compared to the controls'
73.9 % green parthenocarpic caryopses (GPCs) and 41.8 % haploid
embryos (as percentage of pollinated florets, PF) of which 33.3
% regenerated green plantlets (= 13.9 % of PF); the four best
WHs gave the following results:
-WH10: 92.8% GPCs, 42.2 % (of PF) embryos of which 43.3 % regenerated, plantlets (=18.3 % of PF).
-WH11: 84.1% GPCs, 49.8 % (of PF) embryos of which 43.2 % regenerated, plantlets (=21.5 % of PF).
-WH12: 84.6% GPCs, 43.1 % (of PF) embryos of which 38.6 % regenerated, plantlets (=16.7 % of PF).
-WH13:
85.8% GPCs, 36.9 % (of PF) embryos of which 55.1 %
regenerated, plantlets (=20.3 % of PF).
Control = 10 mg/l 2,4-D; WH10 = 30 mg/l picloram
+ 4 mg/l BA; WH11 = 20 mg/l picloram + 15 mg/l 2,4-D + 2
mg/l BA + 75 mg/l GA3; WH12 = 20 mg/l picloram + 25
mg/l 2,4,5-T + 6 mg/l BA; and WH13 = 50 mg/l 2,4-D +
100 mg/l GA3).
The WH solutions containing dicamba induced high
frequencies of GPCs and embryos, but the regeneration of the latter
were poor. A modified MS-culture medium for regenerating barley
anther calli (from G. Daniel, BLBP, Freising, Germany), fortified
with 20 g/l sucrose, 1 mg/l IBA, and 0.5 mg/l BA, was the most
suitable for culturing embryos and regenerating plantlets.
Private Bag X29, Bethlehem 9700, South Africa.
Winter and intermediate wheat breeding.
H. van Niekerk, N. Edwards, M. Jenkins, D. Exley, O. Muller, M. Ncala, and R. Pretorius.
The aim of the winter and intermediate wheat breeding
program is the release of cultivars that are stable, high-yielding
and widely adapted for the dryland conditions in the summer rainfall
region of South Africa. This region is responsible for 50-60
% of the total wheat production in South Africa. Caledon,
a new, intermediate wheat cultivar, was released during 1996.
Caledon has resistance to the Russian wheat aphid, good yield,
and excellent quality characteristics. Seed should be commercially
available during the 1998-99
season. A hybrid wheat project has been initiated to introduce
cytoplasmic male sterility into selected lines.
As part of the RSA-Turkey shuttle-breeding project,
Dr. Hugo van Niekerk visited Izmir, Turkey, to make selections
on the F4 generation. The advantages of shuttle breeding
are the excellent natural stem, leaf, and yellow rust inoculum
in Turkey and the fact that an extra generation is gained each
year. The F3 generation is planted in South Africa
in May, harvested in November, and sent to Turkey for planting
in December-January
as F4s. Selections are made during early June and
replanted in South Africa in late June as F5s. Unfortunately,
this shuttle will no longer operate because of budget constraints,
and another location is being sought.
Several near isolines from a project on aluminum
tolerance were screened using RAPD markers. Of the 120 primers
screened thus far, a number of potential markers have been identified
and these currently are being tested on F2 populations.
An additional 420 primers will be screened to identify more polymorphisms.
The aluminum tolerance backcross program is progressing well
and good selection pressure was encountered for the F2
and F5 generations. These lines were planted on a
piece of land that was artificially `soured'
to achieve an even spread of acidity.
H.A. Van Niekerk, F.P. Koekemoer, A. deVilliers, T.G. Paxton, S. Jordaan, R. Britzen, F. Groenewald, and H. Botha.
The primary goal of the breeding program is to release
commercial cultivars for irrigated and dryland rainfed conditions.
Another activity of the breeding program is directed towards
the development for the Eastern Free State of RWA-resistant cultivars
, which can be grown under irrigation or dryland conditions during
the summer months. We evaluated 7,523 F4 lines and
four replicated senior trials with 36 entries. The first elite
trial will be planted next season. The line BSP94-17 was
withdrawn from provisional release because of a lodging problem.
A total of 186 lines with possible take-all resistance were evaluated at a site where a high inoculum of take-all occurred. The infection rates were not as severe and homogeneous in 1995 as in 1996. Ten replications were planted from each of the 186 entries that showed possible resistance in 1995. These lines were planted again in 1996 to distinguish resistance from avoidance, a factor of growth period. Two lines that have very good levels of resistance were from the cross `SST66/3/KVZ/JAR"S"Plant pathologyPlant pathologyyPlant pathology@//Flicker"S"/5/FMS3*//Trans/FW815-4-2/3/COND/3*AG
/4/Maya74"S"/PVN"S"".
The resistance in these lines is currently being confirmed under
greenhouse conditions.
A study was made to determine the heritability of
certain protein-related characteristics that can be used as selection
criteria to simultaneously increase both protein content and grain
yield. We found that the amount of protein per kernel (as determined
by the whole grain infra analyzer) can be used as a correlated
response index for grain protein yield to increase the latter
in small increments. Grain protein yield had good correlation
(r2 = 0.99) with grain yield. Therefore, an increase
in grain protein yield will generate an increase in grain yield.
The cultivar T4 (Anza) showed good general combining ability
for selection of characteristics that increase biomass and grain
yield, whereas the line BSP91-8 (a T. dicoccoides
derivative) showed good general combining ability for characteristics
that increase protein content.
Stripe rust appeared for the first time ever in the
dryland wheat production areas of South Africa. This airborne
disease apparently migrated from central Africa and has added
in a completely new dimension to our wheat breeding project.
V.L. Tolmay, G.J. Prinsloo, J.H. Hatting, and R. Marae.
The Small Grain Institute is busy implementing an
integrated program for RWA control. The basis of this program
is the use of resistant cultivars, supported by natural enemies
and cultural practices. Chemical control is intended to be used
only when extremely high infestation levels occur.
Five wheat cultivars with RWA resistance, Tugela-DN,
Betta-DN, Gariep, Limpopo, and Caledon, have been released
for commercial production in South Africa. We are studying sources
of RWA resistance with regard to the inheritance and mechanisms
of the resistance. A backcross program is attempting to transfer
RWA resistance to agronomically acceptable lines for use in the
winter and intermediate wheat breeding programs. The resistant
cultivars will be tested under field conditions to compare their
efficacy with chemical control.
The parasitoid Aphelinus hordei was released
in the field for the second year. However, the parasitoid failed
to over summer in the field, mainly because of low RWA numbers
during summer. We are now trying to get alternate RWA host plants
established in the field during summer to ensure that the RWA
population will enable the parasitoid to survive. We are making
studies on the biology of the parasitoid in the laboratory.
The use of entomopathogenic fungi as possible biocontrol
agents for the RWA is being investigated by the SGI. Three fungal
species have been isolated from field-collected specimens of the
RWA and are presently being evaluated at the Institute. Investigations
include culturability on artificial media, storage, production
of conidia, LD50 values, and application techniques.
Additional surveys aimed at isolating new strains and species
are being made in the Western Cape and the irrigation areas of
Kwazulu and Natal.
Willem Boshoff.
Stripe (yellow) rust was observed for the first time
on bread wheat in the Western Cape during August, 1996. Surveys
during the growing season indicated that stripe rust occurred
throughout most of the wheat producing areas in the winter rainfall
regions of the Northern, Western, and Eastern Cape provinces and
on irrigated wheat in the summer rainfall area south of Kimberley.
Stripe rust was most severe in the Western Cape, where prolonged
favorable weather conditions and the high level of susceptibility
of most cultivars favored development of the epidemic and necessitated
extensive fungicides applications. Spike infection and foliage
destruction caused significant losses in grain quantity and quality
in certain fields. All isolates were representative of one pathotype,
characterized by avirulence on the following cultivars/lines:
Chinese 166 (Yr1); Vilmorin 23 (Yr3); Moro (Yr10);
Strubes Dickkopf, `Suwon 92/Omar',
and Clement (Yr2 and Yr9); T. aestivum ssp.
spelta var. album (Yr5); Hybrid 46 (Yr4);
Reichersberg 42 (Yr7); Heines Peko (Yr2 and Yr6),
Nord Desprez (Yr3); Carstens V, Spaldings Prolific, and
Heines VII (Yr2); `Federation*4/Kavkaz'
(Yr9); Avocet-S (Yr15); and virulence to Kalyansona
(Yr2); Heines Kolben (Yr2 and Yr6); Lee (Yr7);
Compair (Yr8); and Federation 1221. The cultivars Trident
(Yr17), Avocet-R (YrA), and Selkirk (YrSk)
appeared heterogeneous for stripe rust reaction. The pathotype
resembled race 6E16, previously detected in east and north Africa,
the Middle East, and western Asia. In view of the rapid dispersal
of the pathogen during 1996, susceptibility of several high-yielding
cultivars, and favorable climatic conditions in many wheat growing
areas, stripe rust is considered potentially damaging to the South
African wheat production. Field observations and seedling tests
have shown, however, that certain cultivars are resistant to the
introduced pathotype. The genetic basis of this resistance is
largely unknown at the present time.
Annelie Barnard.
Preharvest sprouting research is aimed at solving
the problems faced by cereal producers and the cereal industry
regarding its deleterious effects on wheat baking quality. Limited
information is available on field performance of sprouted seed
and plants grown from sprouted seed. As sprouted grain is often
retained for seed, we investigated the effect of seed treatment
and sprouting severity on germination, seedling emergence, yield
components, and yield. Sprouting severity was the determining
factor in all seed treatments. However, seed treatments also
contributed to a decrease in germination and emergence and, consequently,
yield. Sprouted seed considerably decreased stands and yields.
These decreases were proportional to the sprouting severity of
the seed. Yield compensation by yield components was limited.
We are trying to determine the effect of certain
micronutrients, especially molybdenum, on preharvest sprouting
and have completed studies on the `genotype
x environment'
interaction of winter wheat cultivars commonly grown in South
Africa.
Seed testing laboratory at the Small Grain Institute.
Frederieke Bruin.
Successful establishment of wheat and other small
grains depends first on high-quality seed and then on the correct
culture techniques. A growing demand has made seed analyses and
seedling morphology studies available as a service to the small
grain producer, seed and chemical companies, and cooperatives.
A small grain seed-testing laboratory at the Small Grain Institute
has been established. Methods of analyses are prescribed by ISTA,
the International Seed Testing Association, and the laboratory
is accredited locally by the South African Department of Agriculture,
Directorate: Plant and Quality Control, which inspects the laboratory
on an annual basis and also runs a referral program to ensure
international quality standards of the laboratory and the personnel.
Several contracts also have been made with chemical companies
for the evaluation of unregistered (in South Africa) seed treatments.
Our aim is to render an objective and reliable service of seed
analyses to the small grain industry in South Africa.
Foliar diseases and take-all of wheat.
D.B. Scott.
Yield increases in the Western Cape are often obtained
by spraying fungicides on wheat. However, farmers do not spray
their crops with fungicides in South and Western Australia where
similar fungal diseases occur. Leaf necrosis of wheat is commonly
attributed to fungal pathogens S. nodorum and S. tritici
in the Cape, but using field trials with fungicides, the common
occurrence of leaf necrosis in wheat fields was the result of
physiological leaf spot, first described in the United States.
Studies have indicated that physiological leaf spot is associated
with nutrient deficiencies, principally chlorine. Furthermore,
chlorine-deficient plants are very susceptible to take-all
root rot and growth-regulating effects of fungicides are responsible
for yield increases of wheat in the Western Cape.
Personnel.
Nicola Warburton was married during December and
is now Mrs. N. Edwards. Megan Jenkins joined the program as a
winter wheat breeder, replacing Hendrik Knobel who resigned to
join Sensako. Lianae
van Rooyen joined the quality laboratory as a technician, replacing
Magdel Human who returned to University for further studies.
Department of Genetics, Stellenbosch 7600, South Africa.
G.F. Marais, R. Prins, F.L. Middleton, H.S. Roux, and A.S. Marais.
Breeding programs.
Selection programs aiming to develop improved durum
cultivars for the lower Orange River irrigation areas and triticale
cultivars for the southwestern Cape were continued. No new releases
were made, but promising advanced lines with good quality were
selected.
Genetic studies.
A study of four suspected, recombined forms of the
Lr19 translocation showed that only one is a true recombinant.
The translocated segment in recombinant 149 was apparently relocated
from 7DL to chromosome arm 7BL. Combining Lr19 with other
useful genes occurring on chromosome arm 7DL, such as Dn5,
Lr34, Yr18, and Pch-1 may now be possible.
The recombined form expresses complete Lr19 resistance,
is associated with white endosperm color, and has a strong tendency
to self-eliminate in certain genetic backgrounds. The yield
of isogenic lines with Lr19-149 does not differ significantly
from that of their counterparts lacking the segment. Attempts
are being made to find additional molecular markers associated
with the recombined translocation. We initiated a new cycle of
crosses aimed at further reducing the size of the segment through
homoeologous pairing in the absence of Ph1b. The remaining
suspected recombinants (Lr19-63, Lr19-157,
and Lr19-184) lacked Lr19, but did have an
unknown leaf rust-resistance gene (probably derived from the line
Indis). We are attempting to extract the true Lr19 recombinants
among early backcross derivatives of the material using molecular
markers.
Attempts to transfer leaf rust resistance genes from
Aegilops and Triticum species to common wheat were
continued. The most advanced material has reached the BC5
stage. The project will be broadened to also introduce resistance
against this disease, because of the first occurrence of stripe
rust in South Africa in 1996.
Salt tolerance of Th. distichum is suppressed
in its hybrids with common wheat. We are studying its expression in `Th.
distichum x rye' and `Th. distichum x triticale'
hybrids. Although allodiploid progeny was produced for both crosses,
the plants remained pollen infertile and produced only a small
number of apomictic seeds. A backcross of some of the hybrids
to the triticale parent was made, and the hybrids appear to be
salt tolerant. The Thinopyrum cytoplasm per se
does not appear to impart salt tolerance, but it possibly may
interact with nuclear genes.
A gene for stem rust resistance derived from T.
speltoides is associated with a gametocidal gene with very
severe effects. Heterozygotes gametes without the Gc gene
always die, making it impossible to separate the resistance and
Gc genes. Attempts to remove the Gc gene through
irradiation and MNH treatment were unsuccessful. However, when
Gc homozygotes were crossed with certain Chinese Spring
nulli-tetrasomic stocks (such as N3A T3B, N3A T3D, and N6A
T6D) F1 plants that produce seeds on more than 50 %
of their florets were encountered. These crosses may make it
possible to break the association of the Gc and stem rust
resistance genes. The B-genome telosomics are being used
in further attempts to identify the chromosome carrying the Gc
gene.
Publications.
Marais GF and Pretorius ZA. 1996. Gametocidal effects
and resistance to wheat leaf rust and stem rust in derivatives
of a Triticum turgidum ssp. durum/Aegilops speltoides
hybrid. Euphytica 88:117-124.
Antonov AI and Marais GF. 1996. Identification
of leaf rust resistance genes in Triticum species for transfer
to common wheat. SA J Plant & Soil 13:55-60.
Prins R, Marais GF, Janse BJH, Pretorius ZA, and Marais AS. 1996. A physical map of the Thinopyrum derived Lr19 translocation. Genome 39:1013-1019.
INTERNATIONAL CENTER F R AGRICULTURE RESEARCH FOR THE DRY AREAS - ICARDA
P.O. Box 5466, Aleppo, Syria.
Screening durum wheat accessions for boron-toxicity tolerance.
S.K. Yau and J. Valkoun.
Subsoils with above normal levels of boron (B) occur
commonly in dry areas. Boron may hinder root growth into the
subsoil to take up stored moisture and adversely affect yield,
especially in years of drought, besides directly causing B toxicity
to crops not tolerant to B toxicity.
Durum wheat is one of the most important crops in
West Asia and North Africa (WANA). Approximately 85 % of the
total acreage of durum wheat is grown in developing countries,
mainly under semiarid conditions. Screening of advanced lines
from the CIMMYT/ICARDA durum wheat breeding program in previous
years revealed that, unlike bread wheat, only moderate, though
significant, variation between entries in B-toxicity symptom
score (an indicator of degree of tolerance). Furthermore, all
lines had higher symptom scores than the tolerant Australian bread
wheat cultivar Halberd.
We evaluated germplasm accessions from WANA in 1995
in order to find durum material with B-toxicity tolerance
comparable to that of Halberd,. Seedlings were screened in a
plastic house in soil evenly mixed with boric acid at a rate of
100 mg B/kg soil (twice that used in earlier screening), by applying
a hot-water extract of 40 ppm B. Under this condition, sensitive
plants had retarded growth and were yellowish to pale green in
color after emergence. Foliar B-toxicity symptoms and growth
scores were made 4 to 6 weeks after sowing.
In the first screening, 25 random durum wheat accessions
from each of six west Asian countries (Afghanistan, Iran, Iraq,
Jordan, Syria, and Turkey) were tested. The most tolerant durum
accessions were ICDW 9762, 9833, and 9761 from Afghanistan; 7743
and 9975 from Iran; 6267 and 6268 from Turkey; 11470 from Syria;
20869 from Jordan; and 6145 and 7327 from Iraq. These accessions
had growth scores equal to Halberd, and better than the tolerant
durum check, Oued Zenati. Many more accessions from Afghanistan
appeared tolerant, but they later were identified as bread wheats.
Of 50 random accessions from four north African countries
(Algeria, Libya, Morocco, and Tunisia) screened in the second
group, no accessions had a symptom score as low as Halberd. With
the exception of the five most sensitive accessions, all accessions
had symptom scores that were not significantly different from
Oued Zenati. There also were no significant differences in an
accessions' B-toxicity symptom scores between the four countries.
A screening of all accessions in our gene bank from
countries with a higher percentage of tolerant accessions was
made based on these results. A total of 209 accessions, 80 from
Afghanistan, 73 from Iran, and 56 from Iraq, were included. There
were significant differences in the accessions' B-toxicity
symptom and growth scores between individual accessions and between
the three countries. Afghanistan accessions averaged less severe
symptoms and better growth than those from Iraq and Iran. Twenty-four
accessions had a performance score (symptom score plus growth)
better than, or equal to, Halberd, and significantly higher than
Oued Zenati. Twenty-two of these B-toxicity tolerant
accessions were from Afghanistan, suggesting that high-B soils
may be common in that country.
Although B toxicity is known to exist in the Anatolian
Plateau of Turkey, 108 accessions from five provinces in that
region (Yozgat, Nigde, Afyon, Eskisehir, and Kayseri) were screened.
Differences in symptom and growth score between accessions from
the provinces were not significant. Four accessions had a growth
score equal to that of Halberd.
Durum accessions with good symptom and growth scores
were selected for further testing in pots. Preliminary results
indicated that some of these durum accessions had grain-yield
reduction less than Halberd in high-B soils, although they had
higher B-toxicity symptoms.
We concluded that screening at the seedling stage
identified some durum wheat accessions with B-toxicity tolerance
equal to that of Halberd, the bread wheat tolerant check. Most
of these tolerant accessions came from Afghanistan.
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