Studies On Molecular Quantitative Genetics Of Resistance To Aphid In Sorghum

Sorghum is the fifth largest cereal crops in the world with the total yield next only to corn,wheat, rice and barley. Sorghum has characteristics of high photosynthetic efficiency of C4plants and enormous genetic diversity and can be used not only as food crops, but also theforage crops and brewing raw materials. In addition, sorghum has extensive adaptability to theenvironments, strong drought resistance and high yield. Aphid is one of the main pests ofsorghum, outbreaks once every3~4years and leads to a large reduction in production andhuge economic losses. Although pesticides application can control aphids well, unproper useof pesticides might cause human and animal casualties, and increase the cost of production.The most economic and effective ways of sorghum aphid prevention are to clarify sorghumaphid resistance mechanism and genetic rules and to map the accurate positions of aphidresistance genes for the development of sorghum aphid resistant varieties.In this study, sorghum aphid resistant variety TAM428B and the sorghum aphid sensitivevariety Tx622B were selected as parents lines to make F1and F2generations. Parents, F1andF2generations plants were infected naturally or by hand, and aphid quantity were recorded foreach individual plant. Methods of both quantitative genetics and molecular markers wereapplied rather than only those of molecular marker as reported in other studies, which is oneof the innovative parts from this study. Detailed results from all experiments list as follows:Sorghum aphid resistance data fit into well the model of the skewed normal distribution,and are classified as quantitative traits."F2generation separation analysis" and "fourgeneration joint separation analysis" were carried out to analyze the aphid quantity data.Based on the first method, sorghum aphid resistant trait is found to be controlled by two pairsof additive-dominant-epistatic main genes (B-1model) with the main genetic rate66.98%;While analyzed by the second method, this trait is believed under the control of two pairs ofadditive-dominant-epistatic main genes+additive-dominant polygene (E-1model) withthe main genetic rate90.84%and polygene heritability4.77%. The further analysis revealedthat the second method is much stable than the first one, so we finally took the conclusion offour generation joint separation analysis, i.e. the sorghum aphid resistance trait is mediated bytwo major genes and some modifier genes;63primer pairs showing polymorphism betweenparents are screened from the250primer pairs.5out of63pairs of primers demonstratepolymorphism between the "resistance group" and "sensitive group".220lines of F2 population were used for the measurements and the molecular marks Xcup29on the B linkagegroup was found closely linked with aphid resistance trait, and marker screen in range of±10cM around Xcup29identified four molecular markers covering13.4cM genetic distance. Thetarget QTL was mapped to the region between the molecular marks Xcup29and Sam61581explaining24.7%of the total variation as a major QTL, But another major QTL was notfound due to low density of the molecular markers and the interference of environmental cuesthat attentions need to be paid to in the following studies.