부산대학교 도서관

The greenbug [Schizaphis graminum(Rondani)] is a severe pest of wheat (Triticum aestivumL.) in the Great Plains that can cause leaf chlorosis and tissue death. The simultaneous presence of drought and greenbug stress in a wheat crop has frequently resulted in very heavy grain yield losses. Our objective was to quantify the effect of greenbug stress on photosynthetic characteristics of susceptible and resistant growth chamber grown plants both with and without drought stress. Data collected from single infested leaves of susceptible plants (cv. Sturdy) showed greenbug (biotype C) induced decreases in the C assimilation rate (A), transpiration (E), stomatal conductance to water vapor (gs), and total chlorophyll (CHL). No significant effects were noted for water use efficiency (WUE), intercellular CO2concentration (Ci), or specific photosynthetic activity of chlorophyll (A/ CHL). Infestations on a resistant plant (OK 80268) caused a significant drop in E and gs only. Although greenbug damage decreased gs, A vs. Ci response curves for infested and noninfested susceptible plants showed that there was no increased stomatal limitation to A associated with greenbug damage. Carbon dioxide saturated photosynthesis was lowered by about one‐third, indicating a loss of photosynthetic capacity in the mesophyll associated with chlorosis. When greenbug infestations were applied to drounght‐stressed, susceptible plants, sharp drops in WUE and A/CHL were observed in addition to an increase in Ci. The results show that greenbug induced decreases in A were caused by decreased photosynthetic capacity in the mesophyll rather than decreased gs and that drought stress in combination with greenbugs caused damage to the mesophyll capacity for photosynthesis beyond that explained by chlorosis alone.