| Utilization of heterosis has become a successful strategy for increasing productivity of plants and animals, especially for maize and rice. Plant height is an ideal model for the research of genetic basis, because it is less complex and the results may intuitively be more comprehensible. Other advantages are that it has the high level of heterosis and high heritability. Here, an "immortalized F2" population(IF2 population)was produced by randomly permutated intermating among 294 recombinant inbred lines(RIL)form an elite cross Yuyu22. Measurement of plant height for crosses in the 1F2 population were obtained from replicated field trials over 2 years in Beijing and Xunxian,respectively. Using a genetic linkage map, a great number of QTL and epistasis pairs of plant height and heterosis were detected, furthermore, the genetic basis of plant height was analyzed. The main results were summarized as follows:1. A genetic linkage map containing 263 SSR polymorphic markers was constructed, covering a total of 2360 cM with an average interval of 8.97 cM, which was inquite consistency with the linkage maps published by Maizegdb.2. In immortalized F2 population, the homozygousity frequency of Zong3 and 87-1 was 27.76% and 24.12%, respectively, and the heterzygousity frequency was 48.13%, which was similar to those of an F2 population.3. A total of 14 plant height QTL were detected in two locations over 2 years, which were clustered on the chromosome 1, 3 and 5, explaining the phenotypic variance from 3.5% to 21.62%, with an average of 7.45%. Most of them showed part-dominance.4. A large number of significant digenic interaction pairs were identified in IF2 population by two-way ANOVA. The frequency of AA interactions was the highest, followed by AD/DA, while the frequency of DD was the lowest. Each pair explaned the phenotypic variance and heterotic variance were 4.84% and 4.78%, respectively . it clearly demonstrated that epistasis may play an important role in the genetics basis of plant height heterosis in IF2 population of maize.5. Nine genotypes with significant digenic interactions were detected. Two of them, the complementary two-locus homozygotes (11/22 or 22/11) frequently appeared to be the best genotypes, compared with the means of the two parental genotypes (11/11and22/22), but the single heterozygotes (11/12,12/11,22/12andl2/22) may also be the best genotypes in a few cases. And the double htereozygote (12/12) was neither the best nor the worst genotype. The parental two-locus homozygotes (11/11 or 22/22) showed marginal advantages in many cases.6. Using the data of IF2 population and RIL population, a total of 10 heterotic loci, each explaining the variance of heterosis from 0.95% to 8.63% (average 2.75%), were first detected on six chromosomes with a random distribution. Interestingly, some of the heterotic loci and performance QTL overlapped.7. Based on the loci that were polymorphic between the two parents, single-locus heterotic effects (caused by partial-,full-,and over-dominance) and DD interactions were pertinent to the interpretation of plant height heterosis in Yuyu22.
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