Relationship Between Chlorophyll Loss and Photosynthetic Rate in Greenbug (Homoptera: Aphididae) Damaged Sorghum

Abstract

The effect of greenbug, Schizaphis graminum (Rondani) feeding on chlorophyll content and photosynthetic rate in sorghum (Sorghum bicolor (L.) Moench) was assessed un der 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 re duced significantly both photosynthetic rate and chlorophyll content. Photosynthetic rate showed a positive correlation with chlorophyll content (r = 0.36, d.f. = 208, P = 0.0001). With a small drop in chlorophyll content, a drastic reduction in photosynthetic rate was no ticed. Decreased chlorophyll content due to greenbug feeding partially explained the reduc tion in photosynthetic rate. Leaf age, nutritional status, and micro-environmental parameters may also have influenced the relationship between photosynthetic rate and chlorophyll con