Evaluating Uniformity and Stability of Wheat Cultivars Based on Ratio of Homozygous DNA Locus

Abstract

Evaluation of the uniformity and stability is of great importance in the determination of cultivar release. The ratio of homozygous DNA locus ratio is one of the main factors affecting the uniformity and stability of wheat (Triticum aestivum L.) cultivars. To figure out the feasibility of molecular markers in testing the uniformity and stability of wheat cultivars based on the homozygous DNA locus ratio, we examined each 50 individuals of every line of 10 F4, 10 F5 lines and 511 cultivars with 172 pairs of SSR, 99 pairs of EST-SSR, and 76 pairs of AFLP-SCAR primers. The homozygous DNA locus ratio was 82.1–94.5% in the F4 lines and 95.7–99.4% in the F5 lines, and the predicted homozygous DNA locus ratio was 98–100% in the F6 generation according to the homozygous DNA locus ratio of 500 individuals from F5 lines. In the 136 released cultivars and 375 cultivars from the National Regional Trials, 10% were observed with the homozygous DNA locus ratio less than 95%, including 11 released cultivars. Thirteen out of 129 cultivars from the 2007–2008 National Regional Trial for Winter Wheat had the homozygous DNA locus ratio less than 95% according to the test result at 84 loci. Compared with the cultivars whose homozygous locus ratio was higher than 95% (control), eight of the 13 cultivars showed obviously segregation in major agronomic traits, such as plant height, plant type, spikelet number per spike, spike length, spike type and grain color, another five with 94% of the homozygous locus ratio had similar trait variations to the control. The test result of 375 cultivars from the National Regional Trials indicated that cultivars with the homozygous DNA locus ratio less than 90% did not have the uniformity and stability; whereas the most of cultivars with the homozygous DNA locus ratio higher than 95% and part of cultivars with the ratio ranging from 90% to 95% possessed the characteristics of uniformity and stability. The results indicated that molecular markers can be a great supplemental tool in the evaluation of uniformity and stability of new cultivars. Thereby, it is feasibly to be evaluated the uniformity and stability of wheat cultivars based on the homozygous DNA locus ratio. Fifty pairs of SSR, EST-SSR and AFLP-SCAR primers were recommended for testing the homozygous DNA locus ratio and at least two kind of molecular markers were advisable to be used in evaluating the uniformity and stability of wheat cultivars. In this study, the method and practical details were explained with the sample size of 20 individual plants and the test locus number of 50.