ACTIVITY AND DIFFERENTIAL INDUCTION OF CHITINASE ISOZYMES IN SOYBEAN CULTIVARS RESISTANT OR SUSCEPTIBLE TO ROOT-KNOT NEMATODES

Host physiological events in relation to infestation by parasitic nema todes are not well documented. Soybean plant responses to Meloidogyne incognita infestation were compared to resistant (Bryan) and susceptib le (Brim) cultivars at 0, 1, 3, 10, 20, and 34 days after infestation (DAI). The resistant cultivar had higher chitinase activity than the s usceptible cultivar at every sample time beginning at 3 DAI. Results f rom isoelectric focusing gel electrophoresis analyses indicated that t hree acidic chitinase isozymes with isoelectric points (pIs) of 4.8, 4 .4, and 4.2 accumulated to a greater extent in the resistant compared to the susceptible cultivar following challenge. SDS-PAGE analysis of root proteins revealed that two proteins with molecular weights of app roximately 31 and 46 kD accumulated more rapidly and to a higher level in the resistant than in the susceptible cultivar. Additionally, thre e major protein bands (33, 22, and 20 kD) with chitinase activity were detected with a modified SDS-PAGE analysis in which glycolchitin was added into the gel matrix. These results indicate that higher chitinas e activity and early induction of specific chitinase isozymes may be a ssociated with resistance to root-knot nematode in soybean.