EFFECTS OF PLANTING DENSITY, STEM PRUNING TREATMENTS, AND SHADE ON SECONDARY TUBER DEVELOPMENT IN SANDERSONIA-AURANTIACA

The effects of three plant densities (128, 256, and 384 tubers/m(2)), three stem pruning treatments, and shading on tuber weight and inciden ce of secondary tuber production in Sandersonia aurantiaca (Hook.) wer e assessed in a factorial experiment. Pruning treatments were an unpru ned control, a single cut just below the lowest flower at early flower ing, and a multiple cut treatment (as per single cut treatment plus 25 % more stem removed every 2 weeks). Tuber weight and secondary tuber f ormation were significantly affected by both plant density and stem pr uning treatments, but not by shading. Averaged across all pruning trea tments secondary tuber formation was reduced from 25.7 to 0.6% with in creasing plant densities. Mean daughter tuber weight, including the we ight of tubers with attached secondary tubers, was also reduced with i ncreasing plant density (11.4, 7.9, 6.5 g) and with increasing severit y 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/m(2) were there sig nificant responses, with secondary tuber formation declining from 33.7 to 15.5% with increasing severity of pruning. Increasing the plant de nsity from 128 to 256 tubers/m(2) 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 practice s show great promise for controlling secondary tuber formation during commercial tuber production.