Timing of crop maturity in cotton

Cotton is an indeterminate species; the timing of crop maturity is determined by the capacity of the plant to continue the production of new fruiting sites. According to the nutritional hypothesis, the cessation of fruit production (‘cutout’) occurs when the demand on the resource supply by growing fruit leaves none for the initiation of new fruiting sites. The aim of this work was to determine whether differences between cultivars in dry matter production or partitioning contributed to the timing of crop maturity. Growth analysis was conducted on a short- and a long-season cultivar grown in four fully irrigated field experiments. The production of dry matter, as a function of radiation-use efficiency (RUE) and light interception, and its partitioning to various plant parts were calculated as indirect measures of resource supply. The cultivars rarely differed in total dry matter production. When differences were measured, the earlier cultivar produced more dry matter due to greater RUE and light interception. Its light interception was greater due to an earlier production of a larger canopy and not differences in light extinction coefficient. Early in reproductive growth, the shorter-season cultivar consistently partitioned a greater proportion of dry matter into reproductive structures than the long-season cultivar in a pattern consistent with its higher growth rate at that time. There was therefore no indication that fruiting in the long-season cultivar was maintained due to greater dry matter production. While differences in partitioning were found, it is not clear whether this contributed to differences in timing of maturity or was a consequence of an earlier development of fruit demand in the early cultivar due to its higher rate of square production