Study On Genetic Basis Of Heterosis For Important Traits In An Elite Hybrid Of Maize (May Zea L.)

Maize is a kind of important crops with the value of foodstuff, economy, and feedstuff. And it plays an important role in agricultural economy of China. Meantime, maize is one of the crops being used its heterosis firstly. By using its heterosis to enhance yield has become an effective breeding method in maize. In recent one hundred years, the research on genetic mechanism of hererosis has been lagging behind its using in practice of production. This will inevitably affect the more utility of heterosis. So comprehensively researching genetic machnism of heterosis and uncovering the mystery of genetic basis of heterosis have theorial and practical significance. Traditional quantitative genetics has lots of shortcoming. For example, it can only provide the total effect of genes controlling target trait. Other genetic information can not be known, such as the genic numbers of objective trait, the distribution of genes on chromosome, genetic effect of single gene and gene action model, and so on. Since 1980s, the naissance and development of molecular markers technology provide a powerful tool for going deep into the research of genetic basis of heterosis and possibility of thoroughly dissecting all kind of genetic effects.Our objectives here are (1) to dissect genetic components influencing major traits in maize, evaluate the contribution of each genetic component and study the genetic basis of yield heterosis in DNA level; (2) to research gene differential expression between parents and F₁ hybrid in order to know of the relationship between gene differential expression and generation of heterosis in RNA level. The results are as follows.1. A genetic linkage map is constructed, which using 191 F₂ individuals derived from Huangzao4×Mo17 as mapping population and 218 molecular markers as polymorphic loci. 240 SSR and 280 AFLP primers are used to detect polymorphism between two parents, and 91 SSR and 20 AFLP primers which produce 248 usefully polymorphic markers are screened at last. 218 markers of them can be mapped on chromosome. This linkage map spans 2015.5cM of genome with an avarage interval of 9.69cM. Some hot segregation distortion regions of markers are found , its causes and effects on QTL mapping are discussded too. Meanwhile, some viewpoints on the technological policy precisely distinguishing genotypic data are put forward. The reason why using the complementary characteristics of SSR and AFLP can effectively construct high density genetic lingkage map are expounded.2. Using plant height and ear height of maize as model traits, A mixed linearmodel approach and its software is used to detect QTLs with main effect, QTLs involved in digenic interactions and Q X E. In total, 7 QTLs of plant height, 6 QTLs of ear height ,18 pairs of digenic epistatic loci of plant height, 13 pairs of digenic epistatic loci of ear height were detected. 6 QTLs of plant height, 8 QTLs of ear height, and 4 pairs of digenic epistatic loci of plant height and ear height respectively with significant interaction with environments are found too. Genetic components underlying these quantitative traits are analyzed, and the study show that additive, dominance and epistasis are the important genetic basis of plant height and ear height in maize. The facticity of QTLs, the genetic relationship between plant height and ear height, and the illumination of above results for molecular breeding are discussed.3. By using composite interval mapping based on maxed liner model and its corresponding software QTLmapper/V2.0, QTL controling growth date are located. Total of 13 anthesis QTL, 7 silk QTL and 5 ASI QTL are mapped in Shunyi and Changping environments. Epistatic loci including 3 pairs of anthesis, 17 pairs of silking and 5 pairs of ASI are found too. Meanwhile, 3 QTL of anthesis, 3 QTL of silking, 2 QTL of ASI, 1 pair of digenic epistatic loci of anthesis, 3 pairs of digenic epistatic loci of silking and 2 pairs of digenic epistatic loci of ASI are detected to interact with environment. By comparing all kinds of genetic components contributing to phenotypic variation of growth date, the conclusion that additive, partial dominance and epistasis effects are important genetic basis are drawn. The reason of difference for the information of QTL of growth date mapping in different population are analyzed. The relationship between clustered phenomenon of genie distribution and phenotype correlation are given scientific and rational genetic explains. How to use the conclusion mentioned above to improve the quantitative characters and operate corresponding genes are discussed.4. Using composite interval mapping based on mixed linear model, QTL involving 12 yield traits are located, with LOD>2.5 as the threshold deciding whether there is a QTL. There are total of 126 OTL detected in three environments including Xinjiang Shunyi and Beijing, with 10.5 QTL per trait on the average. From the point of gene action model, among 126 QTL, 31% QTL of them are additive, 42.1% of them are partial dominance, 9.5% of them are dominance, 17.5% of them are over dominance. In genneral, most QTL controlling yield and its components performed additive and partial dominance effects, which genie effects should be the major genetic basis of heterosis.