Categories of resistance to greenbug (Homoptera : Aphididae) biotype I in Aegilops tauschii germplasm

Categories of resistance to greenbug, Schizaphis graminum (Rondani), biotyp e I, were determined in goatgrass, Aegilops tauschii (Coss.) Schmal., acces sion 1675 (resistant donor parent), 'Wichita' wheat, Triticum aestivum L., (susceptible parent), and an Ac. tauschii-derived resistant line, '97-85-3' . Antibiosis was assessed using tire intrinsic rate of increase (r(m)) of g reenbugs confined to each of the three genotypes. Neither parent nor the re sistant progeny expressed antibiosis. Mean r(m) values for greenbug I on Wi chita (0.0956), and Ae. tauschii (0.10543) were not significantly different . Mean r(m) values for Wichita and 97-85-3 were also not significantly diff erent. Antixenosis was determined by allowing aphids a choice to feed on pl ants of each of the three genotypes. Ae. tauschii 1675 exhibited antixenosi s, but this resistance was not inherited and expressed in 97-85-3. In exper iments comparing Wichita and Ae. tauschii 1675, greenbug I population distr ibutions were not significantly different on Wichita at 24 h, but were shif ted toward Wichita at 48 h. In the second antixenosis experiment, there wer e no significant differences in greenbug I population distributions on 97-8 5-3 or Wichita at 24 or 48 h. When all three lines were compared, there was no significant differences in greenbug biotype I populations at 24 or 48 h after infestation. Comparisons of proportional dr) plant weight loss (DWT) and SPAD meter readings were used to determine tolerance to greenbug I fee ding. Ae. tauschii 1675 and 97-85-3 were highly tolerant compared with Wich ita. Infested and uninfested Ae. tauschii 1675 DWT was nonsignificant, and infested Wichita plants weighed significantly less than uninfested plants. When Wichita and 97-85-3 were contrasted, DWT of infested and uninfested Wi chita plants were significantly different, but those of 97-85-3 were not. M ean percent leaf chlorophyll losses for the three genotypes, as measured by the SPAD chlorophyll meter, were as follows: Wichita = 65%; Ae. tauschii 1 675 = 25%; and 97-85-3 = 39%. Percent leaf chlorophyll losses caused by gre enbug feeding was significantly different in comparisons between Wichita an d Ae. tauschii 1675, and comparisons between Wichita and 97-85-3, although feeding damage was not significantly different in comparisons between Ae. t auschii 1675 and 97-85-3. These data provided further evidence of the expre ssion of tolerance to greenbug feeding in Ae. tauschii 1675 and 97-85-3.