Influence of soybean aphid biotypes on chlorophyll loss of various soybean genotypes

The soybean aphid , Aphis glycines Matsumura, is a major pest of soybeans in North America. It is a serious pest since it develops large colonies on soybeans, and may cause a yield reduction of more than 40% in severe damage condition. Soybean aphids use piercing-sucking mouthparts to extract phloem sap from the plant tissues. The removal of phloem sap causes reduction in chlorophyll content and in turn affects photosynthetic rate. Therefore, it is important to measure the chlorophyll loss due to soybean aphid feeding. In this study, we used a SPAD-502 chlorophyll meter to measure chlorophyll content on different soybean genotypes due to soybean aphid feeding. Chlorophyll content was measured on infested and uninfested leaves in choice-tests for two aphid biotypes (biotypes 1 & 2). The results showed that susceptible genotypes K072623, KS4202 and K1639-2 (susceptible only to biotype 1) were significantly different in their chlorophyll content between infested and uninfested leaves to the two biotypes; but the resistant genotypes (E07906-2, E06902, LD05-16638 and LD09-15087a) did not show any significant differences to these biotypes. Similarly, SPAD indices showed significantly high chlorophyll loss in susceptible genotypes (ranged from 39% to 41% for biotype 1 and 48% to 52% for biotype 2) compared with the resistant genotypes. Furthermore between biotypes, there were differences in the amount of chlorophyll content and chlorophyll loss for soybean genotypes, though they were not statistically different.