Effects of Injury by Partial Defoliation on Chlorophyll Levels in Leaves of Glycine Max (L.) Merr.

Unifoliolate and trifoliolate leaves of Glycine max (L.) Merr. (soybean, cv. Evans) plants at five stages of development were sampled for chlorophyll content. Unifoliolates showed significantly higher chlorophyll levels than trifoliolates in the vegetative three (V3) and reproductive one (R1) stages, and lower levels in the last three reproductive (R2, R3, R4) stages. Trifoliolates showed no significant differences between different stages or nodes. Injury by partial defoliation to trifoliolate leaves was determined by comparison with that of both unifoliolates and trifoliolates which were not subjected to partial defoliation. Following defoliation, the chlorophyll content of the unifoliolate and trifoliolate leaves from mildly and severely defoliated plants increased significantly compared to leaves of plants not subjected to defoliation in three out of four classes. Significant differences in chlorophyll levels between mild and severe defoliation were not evident in greenhouse experiments, but field experiments showed significant increased in chlorophyll levels of severely defoliated (compared to mild defoliated top trifoliolates under drought conditions and unifoliolates when the field was irrigated. Results using the chlorophyll assay indicated that older leaves of a plant, compared to younger leaves, were the most sensitive with respect to changes in chlorophyll levels in plants subjected to partial defoliation.This investigation was supported by a grant awarded to W.L. Koukkari and B.W. Kennedy from the Minnesota Soybean Research and Promotion Council