This study was conducted to enhance marker-assisted selection (MAS) for soybean aphid (Aphis glycines Matsumura) resistance in breeding programs and to test the associated effect of the aphid resistance gene Rag1 on several important agronomic traits in soybean [Glycine max (L.) Merr.].
The objective of the first study was to test for biotype variation of A. glycines in North America. Six soybean genotypes previously shown to be resistant to the Illinois soybean aphid isolate and two susceptible genotypes were tested with the Ohio and Illinois isolates in nonchoice tests. The same genotypes were also tested with the Ohio isolate using a choice test. In both the nonchoice and choice tests, there was a significant effect of isolate, genotype, and an interaction of the isolate and genotype. These tests demonstrated that at least two A. glycines biotypes exist in North America and that three soybean genotypes were resistant to both A. glycines biotypes.
The objective of the second study was to identify single nucleotide polymorphisms (SNPs) near the A. glycines resistance gene Rag1 from Dowling and fine map the gene on soybean chromosome 7 [linkage group (LG) M]. SNPs closely linked to Rag1 were identified by hybridizing Affymetrix soybean GeneChip microarrays and re-sequencing sequence tagged sites (STSs) and selected regions near the gene. For fine mapping of the gene, 824 BC4F2 and 1,000 BC4F3 plants developed using Dowling as a donor parent and Dwight as a recurrent parent were screened with markers and 12 lines developed from recombinant plants were selected and tested for resistance to the Illinois A. glycines biotype and with SNP markers. These tests mapped Rag1 to a 115 kb interval on soybean chromosome 7. This interval contains several candidate genes including two nucleotide binding leucine-rich repeat (NBS-LRR) genes.
The objective of the third study was to identify SNPs near the A. glycines resistance gene Rag2 from PI 200538 and fine map the gene on soybean chromosome 13 [(LG) F]. PI 200538 is a source of resistance to both the Illinois and Ohio A. glycines biotypes. Ninety-five F2:3 lines derived from the crosses LD02-4485 x (Ina x PI 200538) and 185 recombinant lines having various pedigrees and backgrounds were tested with the Ohio A. glycines biotype and markers. Eight SNP markers were developed from resequencing of STSs near the gene and the gene was mapped to a 1.6 cM interval between two SNP markers. Five recombinant lines with key recombinations within the Rag2 interval were tested for resistance to the Ohio A. glycines biotype and with SNP markers. These tests mapped Rag2 to 213 kb interval defined by two SNP markers on soybean chromosome 13.
The objective of the fourth study was to test the associated effects of Rag1 on several important agronomic traits including yield in two elite Midwest adapted soybean backgrounds. This study was done because sometimes the introgression of resistance genes from nonadapted sources can carry undesirable genes through genetic linkages. To test for associated effects, field evaluations of two backcross populations segregating for Rag1 were conducted in multiple environments with no detectable soybean aphid infestations. This study revealed that Rag1 had no significant (P=0.05) associated effect on yield, plant height, and lodging score in either population. Rag1 was significantly (P=0.034) associated with a two-day delay in maturity in one population, and this maturity delay is likely caused by linkage between Rag1 and gene(s) that delayed maturity. This study indicates that Rag1 can be used for developing A. glycines resistant cultivars without an associated yield reduction in the Midwestern region of the USA.
|Adviser||Brian W. Diers|
|School||UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN|
|Subjects||Agronomy; Plant sciences; Plant pathology|
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