DEVELOPMENTAL RESPONSES OF COTTON GENOTYPES AS AFFECTED BY WATER APPLICATION REGIMES.

Water stress has two primary effects on cotton development depending on when it occurs and its intensity. Stress prior to flowering usually restricts the number of mainstem nodes and the number of fruiting sites; whereas, stress during early boll development results in fruit abortion. Field experiments were conducted over a two-year period (2001 & 2002) using varying volumes and frequencies of application of water to determine their effects on the developmental processes of cotton (Gossypium hirsutum, L.) cultivars differing in degrees of indeterminacy. This was a two-variable experiment with one regime designed to evaluate different volume applications of 0, 3, 4, and 5 gallons per minute per acre (GPMA), delivered on a constant 6-day frequency. The second regime was designed to create stress and recovery cycles by delivering water at a fixed volume (SGPMA) over 3, 6, 9 and 12-day irrigation intervals. Comparisons of the effects of these regimes on plant height, main stem node production, production of fruiting sites, percent fruit retention and final boll number per plant revealed genotypic differences in response to both water volume and frequency regimes in all developmental categories evaluated. Picker-types were more sensitive to water stress but were more responsive to increasing water supply than were stripper-types. Growth habit effects were also apparent in that the determinate types responded to increasing volume per application by producing more fruiting sites and harvestable bolls per plant than the more-indeterminate types. The more-indeterminant types responded to longer irrigation intervals with larger volume per application by producing more fruit than at short intervals. The results suggest not only genetic differences in response to water supply, but also opportunity to develop management strategies to match genetic response. [ABSTRACT FROM AUTHOR]