Chapter 7 COTTON FLOWERING AND FRUITING : CONTROL AND MODIFICATION WITH PLANT GROWTH REGULATORS

Cotton (Gossypium hirsutum L.), by nature, is a perennial woody shrub that possesses an indeterminate growth habit. Through breeding and selection, cotton has been adapted to an annual production system and is currently grown under both semi-arid and humid conditions. As such, the crop is often subjected to environmental extremes and exposed to various stresses that impact its yield. The crop may be more vulnerable to these stresses at key developmental stages, such as flower initiation and boll filling. At present, cotton is not genetically limited for yield, but the ability to retain and mature the fruit that are produced remains a challenge. Because of the indeterminate growth habit, cotton produces fruit over an extended fruiting period. Thus, these fruit are developed under varying moisture, temperature, and light regimes. The fruiting habit of the crop normally proceeds from fruit production commencing at around the sixth node and proceeding upward and out on fruiting branches until it reaches a stage of development referred to as cutout. Each fruiting branch that is produced normally initiates from 1 to 4 fruiting sites, with fruiting continuing upward until around the eighteenth mainstem node. Previous research indicates that the majority of yield is produced from the first and second fruiting sites on main-stem nodes 9 through 14. Reports indicate that as much as 80% of the yield originates at these sites. The obvious question is, “why is this the case.” A major contributor to this occurrence is that of source and sink. The first position fruit on a node constitutes a stronger demand for assimilates and if supplies are limited, the subsequent fruit produced on the fruiting branch suffer the consequences. Because of these growth characteristics, ways to modify and control the flowering/fruiting of the cotton plants are often desirable. The alterations may be accomplished through the use of plant growth regulators (PGRs). An organic substance is considered a plant growth regulator if in low concentrations it promotes, inhibits, or modifies plant growth and development, eliciting responses similar to the ones observed from endogenous plant hormones. However, interactions with the environment and differences in cultural practices are mainly responsible for the complex responses generated by crops to PGRs. Lack of consistency in performance, and the fact that PGRs may not be economically beneficial are some of the limitations for PGR usage.