Effects of shading on sink capacity and yield components of cotton in controlled environments

This study analysed effects of a simulated shade treatment on interactions among reproductive sinks, using pruned (monoculm) plants in growth chambers. Plants were grown under non-limiting water supply and 600 mumol. m(-2).s(-1) PAR, reduced by 40% to simulate shade. Shade was imposed from 7th anthesis onwards, and plant transpiration, dw distribution and phenology were monitored. An index of apparent competition for assimilates (IAC) was calculated by dividing boll load by plant growth rate. Within the inflorescence, shading affected all components of a cascade of events determining sink capacity, including carpel growth, seed number, boll abscission, final seed-cotton dw and partitioning between grain and fibre. In addition to sink down-sizing (abscission, seed number), shade also increased boll growth duration, spreading the demand for assimilates over time. Fibre quality was poor in such situations. Shade also reduced boll appearance rates, thus limiting the number of competing sinks. Organ appearance rates, boll duration and abscission rates were correlated with IAC. The future use of an IAC in the analysis and prediction of sink behaviour in complex plant systems is discussed.