Early water stress on growth, development and yield of high retention cotton

Abstract

The Bollgard II cotton varieties, which contain two genes from Bacillus thuringiensis var kurstaki (Bt) that express proteins toxic to Helicoverpa spp. were recently released in Australia, and they have increased insect protection compared with conventional (non-Bt) varieties with similar genetic backgrounds. Irrigation programs in Australia have been tailored to the lower retention conventional varieties and incorporated a long period of water stress until squaring, followed by full irrigation during the reproductive stage. This management, while proven for low retention conventional varieties may not produce sufficient early biomass to support the higher boll load due to high retention in Bt varieties and may limit their yield potential due to a high competition for assimilates between organs under water stress. This thesis aimed to understand the differences in growth, development and yield of different levels of water availability at pre-flowering in high retention cotton. To achieve this general objective, eight field experiments, seven at Gatton in southeast Queensland and one at Narrabri, New South Wales, were conducted in three seasons (2006/07, 2007/08 and 2008/09). Four of them (Exp. 1, 2, 3 and 4) compared the effects of pre-flowering soil water deficits on fruit retention, boll distribution and yield, and quantify differences on biomass growth, partitioning and phenological development. In four experiments (4, 5, 6 and 7), the effect of early water availability was examined for high and lower fruit retention cases (the latter achieved by flower buds removal), and responses on the dynamics of fruit sink development and assimilate supply were studied. A single Experiment (8) at Narrabri, NSW was conducted to study the responses of pre-flowering irrigation management under furrow irrigation. The effects of water treatments were examined using rainout shelters or plastic cover of inter-row space for designated time period in all the experiments.