Evaluation and identification of soybean aphid resistance sources and mapping of soybean aphid resistance loci in early maturing soybean germplasm accessions.

摘要

Soybean aphid (Aphis glycines Matsumura) has been a major pest of soybean [Glycine max (L.) Merr.] in North America particularly in the northern United States and three Canadian provinces. At least four biotypes of soybean aphid have been confirmed in the United States. Identification of soybean aphid resistance sources in early-maturing soybeans and genetic characterization of new sources of resistance will facilitate to expand the gene pool of soybean aphid resistance and thus will help to develop soybean aphid resistant cultivars. To identify new sources of resistance in early maturing soybeans, 330 soybean germplasm accessions from Maturity Group (MG) I, along with 11 resistant or susceptible checks, were evaluated against soybean aphid in greenhouse by caged (no-choice) and non-caged tests. Germplasm accessions that showed resistance in these tests were then tested in the field under natural infestations supplemented by artificial infestation. In the greenhouse tests, accessions PI 189946, PI 153214, and PI 437075 exhibited low SA levels (<50 aphids plant-1 in caged test and SA score of 1.3 or less in non-caged test) similar to those on resistant checks. Six accessions (PI 378663, PI 603587A, PI 567250A, PI 603326, PI 603339A, and PI 603546A) showed moderate aphid resistance with <135 aphids plant -1 in caged and SA score of 2.3 or less in non-caged test. In the field, PI 567250A and PI 603339A performed similar to resistant checks, and PI 153214 and PI 437075 showed moderate aphid resistance. Across all three tests, PI 567250A and PI 603339A exhibited consistently low levels of aphid infestation and thus may be useful in soybean breeding as newly identified sources of SA resistance. To characterize the genetic basis of soybean aphid resistance in PI 603712, a newly identified resistant gemplasm line, 142 F 2 plants derived from the cross 'Roberts' x PI 603712 and their parents were evaluated for soybean aphid resistance in the greenhouse, and were genotyped with BARCSoySNP6K Illumina Infinium II BeadChip. A genome-wide molecular linkage map was constructed with 1495 polymorphic SNP markers. QTL analysis revealed that PI 603712 possessed two major loci of soybean aphid resistance, which were located on chromosome 7 and 16, respectively. The locus on chromosome 7 was dominantly expressed and positioned about one Mega-base-pair (Mb) far from the previously identified resistance locus Rag1. The locus on chromosome 16 was partially dominant and positioned near the previously identified resistance locus Rag3. Interestingly, two minor loci for susceptibility were also detected on chromosomes 13 and 17 in PI 603712. In developing soybean aphid resistant cultivars through marker-assisted selection, an appropriate combination of resistance loci should be selected when PI 603712 is used as a donor parent of resistance. To dissect the genetic architecture of soybean aphid resistance, genome-wide association study (GWAS) was conducted in a population consisting of 330 early maturing germplasm accessions which were genotyped with the Illumina Infinium SoySNP50K BeadChip. Phenotyping was performed in the USDA-ARS Eastern South Dakota Soil and Water Research Farm near Brookings in summer, 2011. Fourteen loci were identified to be associated with soybean aphid resistance on nine chromosomes, of which seven were not previously reported to carry loci associated with soybean aphid resistance or susceptibity trait. Leucine rich repeat (LRR) family protein and protein kinase superfamily protein were predominant protein associated with soybean aphid resistance or susceptibility. Identification of soybean aphid resistance associated loci in the newer and refined chromosomal regions provides more extensive and in-depth insight of genetic association of the trait in the soybean genome.