Soybean Resistance and Defense Responses Against Aphis Glycines

124 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2005.The soybean aphid, Aphis glycines Matsumara, has become an important pest of soybean [Glycine max (L.) Merrill] in North American since 2000. Host plant resistance is an economical way to control aphids. Soybean resistance against A. glycines was studied by (i) characterizing the antibiosis type of resistance, (ii) mapping the aphid resistance gene(s), (iii) investigating the potential factors associated with aphid resistance, and (iv) identifying resistance-related defense responses. Antibiosis in the resistant soybean genotypes ('Dowling', 'Jackson', and PI200538) was demonstrated by a significant decrease in fecundity and longevity and increased mortality of A. glycines, compared with two susceptible genotypes ('Pana' and 'Loda'). The aphid resistance gene in Dowling and Jackson, tentatively named Rag1 and Rag (Jackson) respectively, were mapped on soybean genetic linkage group M by simple sequence repeat (SSR) molecular markers. Rag1 was flanked by Satt435 and Satt463 4.0 cM and 8.0 cM from Rag1, respectively, in the integrated map from Dowling x Loda and Dowling x Williams 82 F2:3 populations, and Rag(Jackson) was flanked by Satt435 and Satt463 1.9 cM and 7.7 cM from Rag(Jackson), respectively, in the map from Jackson x Loda F2:3 population. Soybean pubescence (trichome) did not confer aphid resistance. The concentrations of different flavonoid and isoflavone chemotypes affected aphid population. Gene expression profiles in resistant (cv. Dowling) and susceptible (cv. Williams 82) soybean genotypes were compared at 6 and 12 h with and without soybean aphid infestation using cDNA microarrays consisting of over 18,000 soybean-expressed sequence tags. Eighty-four genes showed specific responses in Dowling and included genes related to defense and a number of other activities. The induction of the three defense-related genes was earlier and stronger at 6, 12 and 24 h after infestation in Dowling compared to Williams 82 by quantitative real-time PCR. The results indicate that the timing of the activation of the defense response is important in soybean resistance to aphids.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD