Submitted to: American Society of Agronomy Branch Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/1/2003
Publication Date: 2/4/2003
Citation: Dunn, B.L., Baker, C.A., Carver, B.F., Porter, D.R. 2003. A reliable breeding tool to identify bird cherry-oat aphid tolerance in wheat [abstract]. Southern Branch of the American Society of Agronomy, February 2-4, 2003, Mobile, AL. p. 13.
Technical Abstract: Rhopalosiphum padi, or the bird cherry-oat (BCO) aphid, is a significant aphid pest to winter wheat (Triticum aestivum L.) forage and grain production in the southern Great Plains. Selection for resistance requires a bioassay that accurately predicts the direct effects of aphid feeding on root and shoot growth. Our objective was to devise a protocol that could be used in growth chambers to eventually allow discrimination among a large numbers of genotypes. Several experiments were conducted to identify optimal conditions that i) maximize differences in root and shoot growth of juvenile plants between aphid-infested and non-infested treatments, or ii) discriminate between two putative genotypes previously discovered to differ in damage caused by aphid feeding. Experimental factors considered were duration of aphid exposure, growth chamber temperature, positioning of germination pouches, and light exposure during germination. Using those results we developed the following protocol. Five seeds of a given genotype were placed equidistantly in a germination pouch and covered with sand. Ten pouches were arranged in a metal rack as five pairs of two pouches facing each other (one containing a resistant genotype and the other containing a susceptible genotype). One rack of pouches was placed in a tub containing water, azoxystrobin (fungicide), and imidacloprid (insecticide for maintaining aphid-free conditions), while another rack was placed in a tub containing water and azoxystrobin only. Each rack served as the experimental unit for replication. After seven days in the growth chamber at 21 C, nonviruliferous aphids were introduced to the tub of pouches lacking insecticide. The experiment was continued for two weeks, at which time seedlings were dried for two days and weighed for shoot and root mass. With aphid exposure, plants of the susceptible cultivar, 'Patrick', showed a 48% reduction in root mass and a 37% reduction in shoot mass.