Effect of early moisture deficit on growth, development and yield in high retention Bt cotton

Abstract

The release of Bt cotton (Bollgard II®) varieties can provide increased insect protection compared with non-Bt varieties with similar gene backgrounds, leading to increased early boll load due to higher fruit retention. The earlier and higher sink demand on a smaller plant may lead to early cut-out and lower yields of Bollgard II cotton compared with the equivalent non-Bollgard II conventionally managed varieties. While the effect of water stress in cotton have been studied by numerous researchers, it is unclear whether manipulation of water management prior to flowering can increase the vegetative biomass for enhanced provision of assimilates for the development and maturation of the early bolls and maximizing the yield potential of Bollgard II varieties. Traditionally early irrigation management (pre squaring) is less in non-Bollgard II crops as early fruit loss is often encountered and there is less demands on the crop thus limiting stress. Two experiments with the Bollgard II variety Sicot 71BR were conducted at the University of Queensland, Gatton Campus, southeast Queensland to study biomass accumulation and partitioning during vegetative stage until flowering and its effect on reproductive growth under different levels of available water: including well irrigated (WI) over the whole crop season, water stress until squaring (WSS) followed by full irrigation and water stress until flowering (WSF) followed by full irrigation until the end of season. Two methods were used to create the water stress treatments: rainout shelters Experiment 1 and plastic cover of inter-row space in Experiment 2. Plastic was removed when the treatments finished allowing full irrigation to commence. Soil water was monitored frequently to maintain the irrigation treatments. Leaf area index, vegetative and reproductive biomass, retention of bolls were found to increase in well watered treatments. WSF and WSS treatments also reduced the time to cut-out and maturity and produced less seed cotton. The results indicate the earlier irrigation management in Bollgard II cotton can increase early vegetative growth to support greater fruit retention and growth of bolls leading to improved yields.

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