Effects of Shade and Partial Defoliation on Carbohydrate Levels and the Growth, Fruiting and Fiber Properties of Cotton Plants.

Abstract

Reducing light intensities to 32% of full exposure by muslin shades erected at the start of flowering reduced the sum of sugar and starch in the leaves by 24%, in the main stems by 38% and in 14-day-old bolls by 8% (means of heavy, medium and light irrigation). The yield of seed cotton (heavy irrigation) was reduced by 47%, fresh weight of leaves plus stems by 13% and relative fruitfulness from 6.0 to 3.3. Plant height and lengths of longest fruiting branches were increased but the number of nodes decreased. There were small reductions under the shades in various boll and fiber properties other than fiber length[long dash]fiber length, like internode lengths, was increased. Removing one-half of previous leaves and of each new leaf weekly from the start of flowering caused little change in the sums of sugar and Starch in leaves or young bolls but there was a 42% reduction in the main stems. The half-leaf treatment reduced plant height by 28%, number of mainstalk nodes by 5%, fresh weight of leaves plus stems by 30% and yield by 14%; relative fruitfulness was increased slightly. Fiber strength was increased but there was little change in other boll and fiber properties. The effects of the two treatments on fruitfulness are discussed in terms of ratios of vegetative weights to number of bolls (relative fruitfulness) and also, on the basis of recent literature, in terms of auxin and anti-auxin relations. The effects on fiber strength are considered in terms of carbohydrate relations.