Mapping For Genes Conferring Resistance To Soybean Cyst Nematode

Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is the most dangerous disease to cause significant yield losses. Soybean cyst nematode causes yield reductions by feeding on plant nutrients, retarding root growth, and inhibiting Bradyrhizobium nodulation.In soybean (Glycine max (L) Merrill), inheritance of resistance to SCN is quantitative and complex. It involves three to four major genes and several minor genes.We developed the integrated soybean molecular linkage map covering 1951.8cM of soybean genome harboring 355 markers on the twenty non-gap linkage groups, which the length of linkage group varied from 51.6 to 184.4 cM and an average genetic distance between adjacent markers is about 5.47 cM of Kosambi genetic distance.We mapped three major loci conferring resistances to soybean cyst nematode race 4, rhg-R4gl, on LG G, rhg-R4a1 and rhg-R4a2 on LGA2 using 3 genetic populations. The position of rhg-R4g1 on LG G is quite similar to well-known locus rhg1, which has same flanking markers, Satt309 and Satt610.Soybean has a complex genome with 1115Mb and genomic database were still limited to be accessed. With the rapidly development of genome sequencing in two legume model plants, Lotus japonicus and Medicago truncatula. It became more and more possible and feasible to use comparative genomic approaches for cloning the SCN resistant gene. We made 56 SSR primers primers designed based on genomic sequences of Medicago truncatula, and identified 2 markers as cross-species markers in Glycine max and Medicago truncatula, which have two markers bracketing the locus of rhg-R4g3 conferring resistance to SCN R4 in Yinxian Heidou landrace. We established microsyntenic relationship between soybean genetic map of the region of rhg-R4g1 and the BAC contigs, and finally we got the putative homoeologous genes and predicted that the candidate genes encoding disease resistance protein, homeodomain related protei and Ankyrin like protein, respectively. Further functional studies will be carried out and tests for allelism will be also conducted.