QTL Mapping Of Photoperiod Sensitivity And Related Traits And Genetic Detection Of Heterosis In Maize

Photoperiod is a major environment factor affecting plant development, and photoperiod sensitivity of flowering time is an important consideration in plant cultivation and breeding. Maize is short day plant and flowering time is affected by photoperiod, what'more, some tropical varieties do not flower under temperate environmental regimes. Sensitivity to photoperiod limits the potential for successful exchange of germplasm across different latitudes. Therefore, it is vital for maize breeders to understand the genetic basis of photoperiod sensitivity in their efforts to integrate tropical germplasm into temperate zone maize breeding. For resolving the geneticbasis of photoperiod sensitivity in maize, in this research , a population of 207 recombinant inbred lines (RIL) derived from a temperate and tropical inbred line cross were developed, and an immortalized F2 population of 278 F1 cross was constrcted by intercrossing of RILs. The"immortalized F2"and the RIL population were evaluated in five location of three photoperiod environment. The performinance data of photoperiod sensitivity and related traits in RIL population and immortalized F2 popultion were used for QTL mapping and digenic interaction analysis; the values of heterosis were used for dissecting the genetic basis of heterosis per se at single-and two-locus level. The main results obtained in this study were concluded as follow:1. A RIL population derived from a temperate and tropical inbred line cross was constructed. the molecular genotypes deriving from parent Huangzao4 were 28.27%-72.15%, the average homozygous genotypes of Huangzao4 was 46.04%; the molecular genotypes of CML288 were 23.63%-65.40%, and the average genotypes of CML288 was 45.61%; The genotypes of the two parents at the marker loci followed 1: 1 theoretical ratio, so the RIL population was a random one and was fit to be used in conduct genentic linkage map and QTL analysis.2. A set of"immortalized F2"population including 278 single crosses was constructed through three round of intermating of 207 RILs. The molecular genotypes of"immortalized F2"population were deduced based on the RILs population according to the mating design. In the"immortalized F2"population, the molecular genotypes deriving from parent Huangzao4 were 10.14-44.55%%, the average homozygous genotypes of Huangzao4 was 25.22%; the molecular genotypes of CML288 were 7.45-48.79%, and the average genotypes of CML288 was 24.64%; whereas the heterozygous genotypes were 32.52-66.34%%, and the average heterozygous genotypes was 50.14%. The genotypes of Huangzao4, heterozygosity and CML288 at the marker loci followed 1:2:1 theoretical ratio, so the genetic components and gene frequency in"immortalized F2"population were similar as a F2 population.3. A genetic linkage map containing 237 SSR polymorphic markers was constructed using RIL population, spanned a total of 1974.3 cM with an average space between two makers of 8.33 cM.4. A total of 151 QTL were detected in three photoperiod environment for photoperiod sensitivity and related traits using RIL population and immortalized F2 population by composite interval mapping. Out of these QTL, 64 QTL were detected in RIL population; 87 were detected in immortalized population and 28 were detected in both population. Many QTL were detected in different photoperiod environment, as a result, a total of 87 different QTL for photoperiod sensitivity and related traits were detected. Out of these QTL, 32 and 55 QTL were detected in RIL population and immortalized F2 population, respectively, and 16 were detected in both populations.5. Different QTL were detected in different photoperiod environment. qDPS4-2,qPH1-2 and qLN4-3 were detected in three photoperiod environment; QTL for flowering time, plant height and leaf number, under long-day conditions, were found clustered on chromosome 10, while QTL for short day conditions resided on chromosome 3. The QTL in the bin 10.04 region of chromosome 10 were detected associated with photoperiod sensitivity and related traits during long-days. These results indicated that this region might contain an important photoperiod sensitivity element.6. Digenic interactions (epistasis) were detected using all possible loci pairs by two-way analysis (ANOVA) between 237 co-dominant molecular markers, and assessed by 1000 times permutaiton tests. A large number of two-locus combinations involving the entire genome were detected for photoperiod sensitivity and related traits. Most interactions occurred between two loci both showing non-significant effects to traits. It clearly demonstrated that epistasis play an important role in the maize genetics basis of heterosis. In the three interaction types (AA, AD/DA and DD) detected in IF2 population, the AA interactions had highest frequency, followed by AD/DA interactions, and the DD interactions had lowest frequency.7. There were 19 (HL) detected for plant height values of heterosis per se in three photoperiod environment. Some heterotic loci were detected in different photoperiod environment. Most of HL showed part-dominance and some showed over dominance effect.8. A lot of digenic interactions of the heterosis for plant height were identified by using two-way analysis (ANOVA). In short day environment, the AA interactions had highest frequency, followed by AD/DA interactions, and the DD interactions had lowest frequency,while the AD/DA interactions had highest frequency and the DD interactions had lowest frequency in long days.9. Neither genome heterozygosity nor special heterozygosity showed strong relationship with plant height in IF2 population under three photoperiod environments. Comparison of trait Performanee among different genotypes in flanking markers of these QTL showed that heterozygosity did not always show higher Performanee than corresponding homozygosity; only 31.6 % of the markers showed overdominanee,and the phenotype value of most of heterozygosity was between the two kind of homozygosity. These results indicated that the complementation and accumulation of dominance gene may play more important roles in the heterosis of plant height. So the overdominance, partial dominance at the single locus and the interaction effects at two loci were the important contributor to plant height heterosis in the IF2 population.