The influence of greenbug, Schizaphis graminum (Rondani) biotype K, feeding on chlorophyll content and photosynthetic rate in greenbug susceptible sorghum [Sorghum bicolor (L.) Moench] was recorded under artificial light conditions. Between 1500-1750 greenbugs were used to infest a 5 cm X 2.5 cm area on a sorghum leaf by means of a modified double-sided sticky cage. A treatment with cage only on the leaf was also included. The control treatment was leaves with no cages and no greenbugs, which would allow measurement of parameters absent the internal effects of either greenbug feeding or cages. Greenbug infestation intervals of 1, 2, 3 and 4 days reduced significantly both photosynthetic rate and chlorophyll content. With a small drop of 13% in chlorophyll content resulting from one day feeding damage, a drastic reduction of 66 % in photosynthetic rate was noticed. Photosynthetic rate showed a positive correlation with chlorophyll content (r=0.36, df=208, P=0.0001). Decreased chlorophyll content due to greenbug feeding partially explained the reduction in photosynthetic rate. Greenbug resistant and susceptible sorghum hybrids were compared for feeding damage of 1 and 4 days over a 10-day observation period. One-day feeding damage caused greater drops for both photosynthetic rate and chlorophyll content in susceptible line than the resistant line but recovery was more in the resistant line. However, at high levels of four-day feeding damage, chlorophyll content and photosynthetic rate decreased dramatically in both resistant and susceptible hybrids and not much recovery was recorded. Thus the resistant line was physiologically tolerant only at low levels of infestation but under high feeding damage, the resistance mechanism collapsed. Further research on the physiological and biochemical mechanisms involved in sorghum resistance to greenbugs should be initiated to understand this response.
Species 1: Homoptera Aphididae Schizaphis graminum (greenbug)
Keywords: plant resistance to insects, chlorophyll loss and photosynthetic rate
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA