Tillering in Tussock Grasses in Relation to Defoliation and Apical Bud Removal

Abstract

Experiments with five caespitose grass species from temperate and tropical environments showed that the number of lateral shoots (tillers) which emerged following defoliation was not increased by leaving a greater residual leaf area. Increased availability of photosynthate (and perhaps other resources) was effective, however, in increasing the rate of growth and degree of flowering of new lateral shoots in one tropical species, Panicum maximum. In two temperate Agropyron tussock grasses, decapitation (apical bud removal) did not stimulate lateral shoot growth. This indicated that apical dominance was not a factor preventing growth of lateral buds just prior to inflorescence emergence on the parent tillers. However, defoliation, where both terminal buds and foliage were removed from the parent tillers stimulated lateral bud growth. Hormones other than those produced by the apical bud or light quality or intensity may control lateral bud growth in these species. In contrast to the temperate species, lateral bud growth was stimulated by both decapitation and defoliation in the three tropical species. This response is consistent with the model of correlative inhibition by apical dominance.