Effects of planting density, stem pruning treatments, and shade on secondary tuber development in Sandersonia aurantiaca

Abstract

The effects of three plant densities (128, 256, and 384 tubers/m2), three stem pruning treatments, and shading on tuber weight and incidence of secondary tuber production in Sandersonia aurantiaca (Hook.) were assessed in a factorial experiment. Pruning treatments were an unpruned control, a single cut just below the lowest flower at early flowering, and a multiple cut treatment (as per single cut treatment plus 25% more stem removed every 2 weeks). Tuber weight and secondary tuber formation were significantly affected by both plant density and stem pruning treatments, but not by shading. Averaged across all pruning treatments secondary tuber formation was reduced from 25.7 to 0.6% with increasing plant densities. Mean daughter tuber weight, including the weight of tubers with attached secondary tubers, was also reduced with increasing plant density (11.4, 7.9, 6.5 g) and with increasing severity of pruning treatments (11.1, 8.4, 6.2 g). However, the effect of stem pruning on secondary tuber formation was much less than that of plant density. Only at the lowest density of 128 tubers/m2 were there significant responses, with secondary tuber formation declining from 33.7 to 15.5% with increasing severity of pruning. Increasing the plant density from 128 to 256 tubers/m2 reduced secondary tuber formation to a low level (3.2 cf. with 33.7%) on unpruned stems, without affecting the daughter tuber weight (10.5 versus 10.7 g). Such cultural practices show great promise for controlling secondary tuber formation during commercial tuber production.