Integration of Response to Defoliation within Plants of Two Species of Sesbania

Abstract

Plant responses to the environment may occur at the level of individual metamers, branches or whole plants. Plants of two species of Sesbania were defoliated in patterns designed to reveal the level of integrated response. For fieldgrown plants, defoliation caused fruit abortion on the defoliated branches, but not elsewhere, showing that the response is at the branch level. When some of the leaves within each branch were removed, the entire branch showed reduction in fruit set. Greenhouse-grown plants had a simpler overall shape, they were unbranched and so had more limited responses. These plants sometimes responded at the level of one leaf and fruit, but such responses may be equivalent to branch level effects in larger, branched plants. Thus, the size and shape of plants may determine response. The plant species also differed in their responses to defoliation. Both species showed identical, branch-level responses in the field, but greenhouse-grown plants revealed interspecific differences in response to defoliation. Sesbania macrocarpa Muhl. was more affected by defoliation and removal of every other leaf was more damaging than removal of half of each leaf. Sesbania vesicaria (Jacq.) Ell. showed less overall impact of defoliation on reproduction, but was more severely affected by removal of half of each leaf than by removal of every other leaf. These differing reponses may complicate interpretation of the effects of defoliation by natural herbivores. Key-words: Defoliation, metamer, integrated physiological unit, yield components, modular growth