Study On Genetic Effects Of The 6VS·6AL Translocation On Common Wheat

Powdery mildew, caused by Erysiphe graminis Dc. f.sp.tritici Marchal, is one of the major diseases of common wheat worldwide. Development and utilization of wheat cultivars with resistance gene is an efficient, economic and environmentally safe strategy to control powdery mildew. T. aestivum-H. villosa 6VS/6AL translocation lines were highly resistant to powdery mildew with resistance gene Pm21 located on chromosome 6VS. The 6VS.6AL translocation lines have been extensively used as resistant parents in crossing programs and several cultivars, such as Shimai 14, Xingmai 2, Neimai 9 and Nannong 9918, with resistance to powdery mildew were released in Hebei, Sichuan and Jiangsu. When alien chromosomes or chromosome fragments carrying target genes are transferred to wheat, undesirable traits can be introduced simultaneously. In order to make full use of 6VS/6AL translocation line in breeding program, research work on translocation chromosome identifying in wheat background, effects of the 6VS/6AL translocation on agronomic traits and quality characters in different genetic background and translocation chromosome transmission has been done as follows:Powdery midew resistance tests, chromosome C-banding, fluorescence in situ hybridization(FISH) and a co-dominant PCR marker(NAU/Xibao15₉₀₂ for 6VS, NAU/Xibao15₉₈₄ for 6AS) were used to assay for 6VS/6AL translocation chromosomes in different genetic background in order to confirm the tested materials from different ecological zones. The resistance tests, C-banding, GISH and PCR results confirmed that two 6VS/6AL translocation chromosomes were present in 18 derivatives aomong 22 tested materials. STS-PCR marker made it possible to screen a large number of genotypes reliably and rapidly in practical breeding programs for the presence/absence detection of 6VS/6AL. Thus, it is highly reproducible and reliable, and can be used in breeding program.Twenty-one common wheat cultivars and advanced lines carrying a 6VS/6AL translocation and five parents, three pairs of advanced lines with and without the 6VS/6AL translocation chromosomes and five crosses F₂ were selected and analysed for agronomic traits and quality characters including grain protein and dough properties of wheat to understand the effects of the 6VS/6AL translocation on agronomic characters and quality characters in different genetic background. In general, there were no significant differences between 6VS/6AL lines and their recurrent parents in agronomic, including grain yield, grains/spike and grain weight/spike. 6VS/6AL lines showed slightly but significantly higher thousand-kernel weight, flag leaf area and plant height. However, significant variation occurred for all traits among sister lines from the same cross and among different crosses, indicating that additional selection and parent selection could lead to further improvements. In quality traits, no significant difference was observed between 6VS/6AL derivatives and their recurrent parent in grain protein, mixograph dough properties and farinograpg. Maybe 6VS/6AL translocation has some positive effect on Zeleny sedimentation and extensograph. Starch pasting characteristics measured by Rapid Viscosity Analyzer varied with genetic background and growing locations, better starch pasting characteristics would be obtained by selecting suitable parent and locations. However, 6VS/6AL derivatives show slight, but significant negative effect on test weight and flour yield. Thus, selection for these traits should be taken into account in breeding when using 6VS/6AL translocation line as parent. It is concluded that 6VS/6AL translocation can be used in wheat breeding programs as valuable donor for resistance to powdery mildew with no obvious undersirable effect on agronomic traits and bread making quality traits.The 6VS/6AL translocation line 92R137(highly resistant to powdery mildew) were respectively crossed to common wheat varieties Bainong 64, Bainong 9310, Han 5310, Xiaoyan 54, Huaimai 20 and Xumai 856 introduced from different areas of China and hybrids F₁ were backcrossed with respective varieties as male and female. Fluorescence in situ hybridization(FISH) on hybrid F₁ PMC at MI was used to study the pairing of 6VS/6AL translocation chromosome of hybrid F₁ in different wheat background. The rod bivalent formed by 6AL of translocation chromosome and chromosome 6A was observed in(translocation line×different variety) F₁ plants. All the F₁ plants expressed high resistance to powdery mildew. It indicated that Pm21 gene on 6VS inherited dominantly and expressed well when transferred to different wheat genotype. In hybrid F₂, there were 69.0%—74.0% plants highly resistant to powdery mildew, close to the transmission of one dominant gene expected value of 75%. In general situation, 6VS can not pair and crossover with 6AS, so powdery mildew resistance and molecular marker on 6VS can be together used to trace the transmission of 6VS/6AL translocation through gametes. The result of testcrosses showed that translocation chromosome 6VS/6AL can transmit to offsprings stably, and the transmission frequency of 6VS/6AL was higher through female gametes(49.2%) than through male gametes(44.7%), but all of them had not significant difference with expected value of 50%.