Apex, lamina and shoot removal effects on seed production and growth of Stylosanthes hamata cv. Verano

Abstract

Swards of Stylosanthes hamata cv. Verano were simulated by growing plants in irrigated square pots placed edge to edge and discarding border rows. The effects on the events leading to seed formation of removing (1) all shoot apices, (2) apices plus 60% of laminae and (3) shoots supporting 60% of laminae were studied, when these treatments were applied at (1) a vegetative stage, (2) early floral initiation and (3) advanced floral initiation. Defoliation delayed flowering and reduced growth rates for 10–30 days subsequently, these effects increasing if bud sites were removed in addition to lamina and apices. In this heated glasshouse the final seed yield and most of the seed yield components were similar in all treatments, including undefoliated swards. Seed yield increased from 141 to 171 g m^-2 when 60% of laminae only were removed at an early seed-setting stage in well-grown swards (LAI 6.9). In a subsequent experiment, removal of 33% of laminae at a similar advanced developmental stage increased seed yield from 106 to 180 g m^-2, and other late defoliation treatments did not significantly influence seed yield. These effects are discussed in terms of altered patterns of apical dominance and leaf differentiation, bud site removal, assimilate supply to the inflorescences, and the consequences of delayed flowering.