Environmental and Cultivar Effects on Height-to-Node Ratio and Growth Rate in Acala Cotton

Cotton (Gossypium hirsutum L.) yield is influenced by the balance between vegetative and reproductive photosynthate demands. We evaluated plant measurements that detect this balance with the objective of developing effective management tools. The effects of water stress, mepiquat chloride (MC; 1,1-dimethylpiperidinium chloride), and cultivar on this balance were evaluated. Plant height is more sensitive to stress than is number of nodes, so that the ratio of height to number of nodes (height-to-node ratio or HNR) provides a useful, field-implementable measure of integrated source-sink balance before anthesis. The rate of increase of height as a function of increase in number of nodes (growth rate or GR) provides a measure of the present state of the balance. Prior to anthesis HNR and GR provide a measure of source strength and accurately detect the ability of crops to sustain vegetative growth as affected by various plant stresses. At maturity, HNR provides an integrated measure of the crop's overall stress level and balance between vegetative and reproductive growth. Research QuestionCotton's response to various environmental factors suggests that the relationship of plant vegetative growth, particularly height and node development, to these environmental factors provides useful indices for crop management. The ratio of plant height to number of main stem nodes, or height-to-node ratio (HNR), and the rate of change of plant height with respect to number of mainstem nodes (MSN), or growth rate (GR), serve as such indices prior to anthesis, particularly in the semi-arid West, where relatively precise water management is possible. These indices can be used to precisely measure the balance between vegetative and reproductive growth. Reference values for HNR and GR have been established for Acala cotton. The objective of this study was to determine the effect of cultivar and environmental factors, particularly water stress and plant growth regulators, on these indices. Literature SummaryResearch conducted to understand the relationship between vegetative and reproductive cotton growth has engendered studies on the competitive nature of this relationship and its source-sink interaction. Methods of controlling vegetative growth and development for the benefit of reproductive growth have been explored using irrigation and N management as well as growth regulators to moderate vegetative development. Studies reported in the literature support the concept that, during the early season, the rate of nodal development in cotton is less affected by environmental stress than is the rate of growth in height. Leaf removal experiments involving removal of one or both cotyledons and removal of zero, one, or two first true leaves at varying days after emergence indicate that many removal combinations significantly affect plant height, whereas only the most severe removal combinations significantly affect number of MSN. In irrigated production systems, delaying the first irrigation significantly reduces plant height. Study DescriptionTwo separate studies were used to determine the relationship between water stress, plant height, and number of MSN. Acala ‘SJ-2’ and ‘GC-510’ were grown in all experiments. Height and MSN were monitored in an irrigation trial conducted from 1986 through 1988 in 40-in. row spacing in which data were collected from 10 randomly selected plants in each of four replicates throughout the growing season. Height and MSN were monitored in a mepiquat chloride trial conducted from 1988 through 1991 in which data were collected from 22 tests conducted in 30-in. row spacing. Applied QuestionsHow are plant height and node development influenced by water stress, and does this response depend on cultivar? Plant height is more sensitive to stress than is number of nodes during the period prior to anthesis. Response to stress was similar in both cultivars tested. Do these measures of vegetative growth provide a sensitive index of crop health and vigor? The ratio of height to number of nodes (HNR) provides a measure of the balance between vegetative and reproductive growth, and rate of increase of height as a function of increase in number of nodes (GR) provides a measure of the present state of crop vigor prior to anthesis. During this period, these indices provide a measure of source strength and accurately detect ability of crops to sustain vegetative growth as affected by various plant stresses. Are these useful, field-implementable indices for managing the balance between vegetative and reproductive crop growth? HNR and GR measurements prior to anthesis provide managers and researchers with quantitative data on the balance between vegetative and reproductive growth and can provide insight into cultural management to improve production efficiency. With more precise information on the balance between reproductive and vegetative growth, the grower can adjust the application of water, nutrients, and plant growth regulators to maintain the proper balance between these growth forms. HNR measurements at crop maturity provide a retrospective indication of the: crop's overall stress level during the season. RecommendationsEvaluating HNR. and GR relative to reference values such as those established here for California may provide a common reference to document the impact of cultivars and stress factors in other environments. Research should be encouraged to document the impact of various other forms of stress on these important measures of vegetative growth, as well as to develop reference values for other cotton growing areas. The issue of whether these indices are useful in cotton growing areas in which the environment is less controllable than it is in the West should be Further explored.