ITEMS FROM THE PEOPLES REPUBLIC OF CHINA

CHINA AGRICULTURAL UNIVERSITY

Department of Plant Genetics & Breeding, Beijing 100094, P.R.China.

Heat tolerance in wheat and its genetic control.

Qixin Sun, Ruqiang Xu, Xiyong Chen, and Shuzheng Zhang.

The relationship between photosynthesis and heat tolerance in wheat. Different wheat cultivars have different responses to high temperature. Four wheat cultivars with different heat-tolerance levels were selected in the field, and the photosynthetic rate of flag leaf under conditions of high temperature was investigated during the grain-filling period. The results showed that the heat-tolerant cultivars Nongda 93 and Nongda 96 have higher photosynthetic rates than the heat-succeptible cultivars Fengkang 13 and Jing 411. Thus, photosynthesis could be critical to heat tolerance in wheat.

The response of winter wheat genotypes to high temperature stress: The differential responses of 28 winter wheat genotypes to high-temperature stress during grain-filling were studied. To obtain high-temperature stress conditions, genotypes were sown in the autumn and put under a plastic cover for 4 days after anthesis. Adaptability to high temperature was estimated using a calculated index, which shows obvious differences between genotypes. A correlation analysis indicated that the above-mentioned methods could provide a simple and reliable heat-tolerance screening technique in the field. In addition, susceptibility indices of some genotypes were found to be correlated positively with their grain yield potential per plant or per spike (r = 0.371* and 0.377*, respectively), but some high-yielding genotypes proved to have poor heat tolerance.

Combining ability and heterosis of cell membrane thermostability in common wheat. Cell membrane thermostability is known to be one of the phsiological parameters for the screening of heat tolerance of wheat in the field. Two sets of a '6 x 6' complete diallel (including the reciprocal), one of six winter wheat cultivars and another of six spring wheats, were used to investigate the combining ability and heterosis of this trait expressed as relative injury (RI %). The results showed that effects of both general and specific combining abilities differed significantly, indicating that both additive and non-additive gene actions were involved in the genetic control of heat tolerance. Reciprocal effects also were found to be significant for both sets of the diallels, indicating that the maternal and cytoplasmic effects also were involved in the genetic control of heat tolerance. Significant heterosis over the midparent and over the more tolerant parental lines also were found for the heat tolerance as measured by the membrane thermostability test. Among the 30 spring hybrids, 17 showed heterosis over midparent, and three hybrids showed heterosis over the more tolerant parent. Among the 30 winter-type hybrids, seven had heterosis over the midparent, and 16 over the more tolerant parent.

The chromosomal location of the genes for heat tolerance was measured by membrane thermostability for the common wheat cultivar Hope. Intervarietal chromosomal substitution lines between Chinese Spring (recipient) and Hope (donor) were used, because Hope was found to be more heat tolerant than Chinese Spring in our previous tests. Significant differences exist among the substitutions (Table 1). When chromosomes 1A, 2A, 2B, 2D, 3A, 3B, 3D, 5D, and 6B of Chinese Spring were substituted by their Hope homoeologues, the heat tolerance of Chinese Spring was significantly increased, but the other substitutions showed no difference from Chinese Spring in their heat tolerance. Thus, chromosomes 1A, 2A, 2B, 2D, 3A, 3B, 3D, 5D, and 6B of Hope have gene(s) for its heat tolerance, and chromosomes 1B, 1D, 4A, 4B, 4D, 5A, 5B, 6A, 6D, 7A, 7B and 7D are not associated with heat tolerance. Although nine chromosomes are associated with heat tolerance, the effect of the different substitutions are quite different. Chromosomes 2A, 2B, 2D, 3A, and 3B have a more significant effect than 1A, 3D, 5D, and 6B. Substitution lines 2A, 2B, and 3B had increased heat tolerance equal to that of Hope, suggesting that these three chromosomes are important in controlling heat tolerance, or they carry major QTLs for heat tolerance.

Based on the above results and our previous study on the tetraploid wheat cultivar Langdon (Sun and Quick 1992), chromsomes of the homoeologous groups 3 and 4 are mostly associated with heat tolerance in tetraploid wheat, whereas those of homoeologous groups 2 and 3 are identified with heat tolerance in hexaploid wheat. The group 3 chromosomes are most likely associated with heat tolerance for both teraploid and hexaploid wheats. These results indicate that although heat tolerance is an quantitatively inherited character, some chromosomes are significantly more important than others. Because some substitution lines become as tolerant as the donor parent, the existence of a major gene or QTL on the related chromosomes is suggested.

* and ** significantly different from Chinese Spring at the 0.05 and 0.01 level, respectively.

Genetic diversity in elite wheat cultivars revealed by random amplified polymorphic DNA.

Qixin Sun, Zhongfu Ni, Zhiyong Liu, Jianwei Gao, and Tiwcheng Huang.

In order to improve heterosis of hybrid wheat, it is necessary to establish wheat heterotic group. This study evaluated the genetic diversity revealed by RAPD markers in elite wheat cultivars and assessed the feasibility of identifing wheat heterotic groups using RAPDs. Thirty-eight winter wheat genotypes from northern China and two spring wheat genotypes from Canada were used for the RAPD analysis. Of the 59 arbitrary 10-mer primers tested on the 40 genotypes, 29 (49 %) detected polymorphism. A total of 168 products were amplified with the 29 primers, and 78 (46 %) of these were polymorphic among the 40 genotypes. The polymorphic products amplified by each primer ranged from 1 to 6, with an average of 2.7. The 78 polymorphic products were used to calculate Nei's similarity index (GS), and a cluster analysis was performed based on the genetic distance (GD = 1­GS) matrix by using the UPGMA method. The GD values ranged from 0.103 between two Chinese wheat lines H88-65 and CA9070 to 0.519 between the Chinese wheat line 10060 and the Canadian cultivar Roblin. The average was 0.256. The average GD value among the 38 Chinese wheats (0.244) was lower than that between the 38 Chinese wheats and the two Canadian wheats (0.372). Thus, less genetic diversity may exist in the winter wheat cultivars. The cluster analysis performed on the GD estimates revealed that the 38 Chinese winter wheats were distinctly separate from the two Canadian spring wheat lines. Two groups were identified among the 38 winter wheat lines, one with four and and one with two subgroups. We noted that lines from the same breeding program tend to be grouped in the same subgroups. RAPD markers are useful in performing cultivar fingerprinting, determining genetic diversity, and identifying heterotic groups of wheat.

Genetic relationships and diversity among Tibetan, common, and European spelt wheat revealed by RAPD markers.

Qixin Sun, Zhongfu Ni, Zhiyong Liu, and Jianwei Gao.

An endemic hexaploid wheat found in Tibet, China, was classified taxonomically as a subspecies, T. aestivum ssp. tibetanum. Seven accessions of the Tibetan wheat, 22 cultivars of common wheat, and 17 lines of spelt wheat were used for a RAPD analysis to study their genetic relationships and to assess the genetic diversity among and within the taxa. RAPD polymorphism was much higher within the spelt and the Tibetan wheat groups than within common wheat. The GD value between the Tibetan and common wheats was lower than that between the Tibetan and spelt wheats. Cluster analysis showed that the 46 genotypes were classified distinctly into two groups. Group 1 included all European spelt wheat lines, and group 2 included all the Chinese common wheat and the Tibetan wheat accessions. However, the Tibetan wheat was substantially different from the Chinese common wheat at a lower hierarchy. Our results support an earlier classification of the Tibetan wheat as a subspecies of common wheat. Spelt and Tibetan wheat have a much higher genetic diversity than common wheat, which could be used to diversify the genetic base for common wheat breeding.

Production of intergeneric hybrid between wheat and apomictic Elymus rectisetus and its molecular identification.

Qixin Sun, Jianwei Gao, Zhongfu Ni, and Zhiyong Liu.

An intergeneric hybrid between wheat and an apomictic E. rectisetus accession (1050; kindly provided by Dr. R.C. Wang, USDA-ARS, Logan, UT) was obtained through sexual hybridization followed by embryo rescue. Genomic DNA was isolated from the seedlings of the putative intergeneric hybrid and parents and was used for RAPD analysis. Among the 105 primers, 102 were polymorphic between the parents. The amplification products from 21 primers are codominant, those of 20 primers are maternal-like, and those of 61 primers are the same as the male parent. Thus, the hybrid we obtained is a true hybrid that will be useful for further experiments attempting to transfer the apomixis genes from E. rectisetus into wheat.

Morphology and cytogenetics of an intergeneric hybrid between Triticum aestivum and an apomictic Elymus rectisetus.

Jianwei Gao and Qixin Sun.

The intergeneric F1 hybrid between T. aestivum cv. Fukuhokomugi and the apomictic E. rectisetus accession 1050 was vigorous and perennial in growth habit but completely male sterile. The F1 hydrid was morphologically intermediate between their parents but generally resembled the male E. rectisetus parent. The hybrid had 63 chromosomes, 21 from T. aestivum and 42 from unreduced pollen of Elymus parent. Examination of PMCs at metaphase I revealed an average chromosome pairing pattern of 22.69 I, 16.15 rod II, 3.01 ring II, 0.83 III, and 0.01 IV. The hydrid and the male Elymus parent were highly resistant to powdery mildew. Production of an intergeneric hybrid between T. aestivum and apomictic E. rectisetus will be useful for transfering the gene(s) for apomixis and resistence to powdery mildew from E. rectisetus to wheat.

HENAN ACADEMY OF AGRICULTURAL SCIENCES

Wheat Institute, Zhengzhou, Peoples Republic of China.

Zuoji Lin, Shenhui Jie, Zhenshen Lei, and Qingru Lai.

1996­97 season.

Precipitation during sowing was sufficient, and rainfall during mid-spring and grain filling was timely. Head number and kernels per spike were higher, and 1,000-kernel weight was similar to that of the 1995-96 season, although powdery mildew and sharp eye spot were more severe than in the previous year. The total yield still had a significant increase and was higher than yield in any previous year.

New cultivar registered.

A new cultivar with both high-yield capacity and good quality was registered in 1997 as Yu-mai No.47. The average yield of Yu-mai 47 was about 7 T/ha, flour protein content was approximately 14 %, and the W value of Alveograph was higher then 300. Backing tests indicated that Yu-mai 47 is suitable for French bread production.

Space mutation breeding.

Eight varieties with different preflight treatments were aboard a satellite in space. Approximately 3,000 head lines of an SP2 were harvested and sown at different Institutes during the 1997 growing season. Some favorable mutations were observed at the seeding stage.

NANJING AGRICULTURAL UNIVERSITY

Wheat Research Laboratory, Weigang 1, Nanjing 210095, P.R. China.

Guo-Liang Jiang, Shi-Rong Yu, Xi-Zhong Wei, You-Jia Shen, Yong Xu, Zhao-Xia Chen, and Shi-Jia Liu.

Breeding for resistance to scab in wheat.

Development of a gene pool with improved resistance through multiple-parent crossing and recurrent selection, using the dominant male-sterile gene Ta1(ms2), is a new approach to breeding for resistance to scab or FHB in wheat. After more than 10 years of experiments, some desirable scab-resistant germplasm resources have been developed jointly by this method and conventional selection, including multiple-site evaluation and shuttle breeding. Compared with the parents, these new lines obviously have improved resistance and agronomic traits. W14 and Changjiang 9306, 9307, and 9311 possess higher resistance to disease spread, shorter plant height, and better yield traits than the well-known resistant cultivar Sumai 3. Compared with the widely grown cultivars Yangmai 5 and Yang 158, Changjiang 9403, with a larger spike, has stronger resistance to scab and lodging and higher yielding capacity (outyielding by 5-10 %).

Preharvest sprouting and resistance characteristics of cultivars of white-grained wheat.

Forty-eight white and two red wheat genotypes were evaluated for preharvest sprouting on spikes and resistance characteristics in three crop seasons. Sprouting percentage on spikes (SPS) and germination percentage of threshed grains (GPG) were measured before harvest. Seed dormancy period, alpha-amylase activity, falling number, water uptake rate, and inhibition percentage of a glume-extracting solution on seed germination were determined after harvest. Significant varietal differences occurred in SPS, GPG, and dormancy period. The sprouting susceptibility varied with year and stage of seed development. Sprouting on spikes and genotypic differences appeared to be more obvious 35-40 days after anthesis. Seed dormancy was associated closely with sprouting resistance, and the average correlation coefficient was - 0.7855**. The correlation coefficients between sprouting percent and seed a-amylase activity, falling number, and water uptake rate in 4 and 8 hours were 0.6789**, - 0.5490**, 0.3574*, and 0.4413*, respectively. An inhibition effect of a glume-extracting solution on seed germination was found, and the genotypic differences were especially clear at 24 h after seed soaking. Such an effect was greater in most resistant cultivars than in the susceptible lines, but it was not important for sprouting resistance in some resistant cultivars. Sprouting resistance in white wheat is complex. Seed dormancy plays a major role, and a-amylase activity, falling number, and glume substances also have remarkable effects on the resistance expression. The resistance mechanism in different cultivars might not be the same.

Personnel.

Dr. Guo-Liang Jiang has returned from the Netherlands after finishing a visit of 6 months. From July, 1997, to January, 1998, he worked with Dr. Rients Niks in the Department of Plant Breeding, Wageningen Agricultural University. His research project was on the inheritance of partial resistance to P. hordei in barley and the interaction between cultivars and isolates.

Publications.

Jiang GL. 1997. Breeding for resistance to Fusarium headblight in wheat. Cereal Res Commun 25(3/2):757-760.

Jiang GL, Chen ZX,, and Wu ZS. 1997. Comprehensive population improvement of scab resistance and agronomic traits in wheat. Cereal Res Commun 25(3/2):663-665.

Jiang GL, Chen ZX, and Wu ZS. 1997. Studies on the development of scab resistant gene pool in wheat. V. Comparison of the effects of population improvement of different gene pools. Acta Agron Sinica 23(1):34-38.

Jiang GL, Chen ZX, Xu Y, and Wu ZS. 1997. Studies on the development of scab resistant gene pool in wheat. VI. Comprehensive analysis and comparison of the scab resistance and agronomic traits of recurrent selection strains and their original parents. Acta Agron Sinica 23(3): 326-332.

Chen ZX, and Jiang GL. 1997. Preliminary study on inheritance of pre-harvest sprouting resistance in white wheat germplasm. J Nanjing Agric Univ 20(3):1-6.

Jiang GL and Chen ZX. 1998. Analysis of combining ability for preharvest sprouting tolerance in white-grained wheat germplasm resources. Acta Agron Sinica 24:in press.

Jiang GL, Chen ZX, Liu SJ, and Xiao SH. 1998. Pre-harvest sprouting in white wheat and resistance characteristics of cultivars. Acta Agron Sinica 24:in press.