Growth and dry matter partitioning of diverse cotton genotypes M.P. Bange * , S.P. Milroy CSIRO Plant Industry, Australian Cotton Cooperative Research Centre, Locked Bag 59 Narrabri, NSW 2390, Australia Received 24 February 2003; received in revised form 8 September 2003; accepted 11 September 2003 Abstract As cotton is an indeterminate species, the timing of crop maturity is largely 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 increases to a point where no resource remains for the initiation and support of new fruiting sites. Thus dry matter production could impinge both on the timing of crop maturity and yield. The aim of this work was to determine the extent to which cotton genotypes of diverse genetic background varied in their growth determinants and dry matter partitioning and how this related to crop maturity. Two field experiments were conducted, each involving two sowing times to provide variation in effective season length and growing conditions. Growth analysis showed little difference in growth characteristics of eight genotypes that would affect timing of crop maturity. Allometric plots showed that partitioning to the fruit began earlier in early genotypes but there was little systematic difference in the rate of partitioning after the onset of reproductive growth. The timing of crop maturity (60% bolls open) was related to the time when the growth rate of the fruit per unit area was equal to the crop growth rate (CGR). Taken together, the results imply that the key trait driving maturity was the timing of the onset of reproductive growth and the subsequent development of the demand for dry matter. Crown Copyright # 2003 Published by Elsevier B.V. All rights reserved. Keywords: Gossypium hirsutum; Development; Radiation use efficiency (RUE); Light interception; Canopy extinction coefficient 1. Introduction In the study presented in this paper we explored the degree of variation in growth and dry matter partition- ing among eight cotton genotypes of diverse growth habit and how these may affect crop maturity. Because cotton is an indeterminate species, the timing of crop maturity is largely determined by the capacity of the plant to continue the production of new vegetative organs and the associated fruiting sites. As the crop develops, the rate of fruit production and the rate of fruit retention both decline. Following the nutritional hypothesis of Mason (1922) and based on crop level measurements, Hearn (1969, 1972, 1994) proposed that both these processes are related to the ratio between rate of accumulation of boll dry matter and crop growth rate (CGR). In support of this, Guinn and co-workers suggest that the imbalance between photosynthate supply and demand is a major cause of this process (Guinn, 1974; Mauney et al., 1978; Guinn, 1985), although the involvement of mineral nutrition or plant hormones cannot be excluded (Guinn and Brummett, 1989). The dynamics of dry matter production and repro- ductive demand may also have significant impact on yield of different genotypes (Wells and Meredith, Field Crops Research 87 (2004) 73–87 * Corresponding author. Tel.: þ61-2-67991540; fax: þ61-2-67931186. E-mail address: michael.bange@csiro.au (M.P. Bange). 0378-4290/$ – see front matter. Crown Copyright # 2003 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2003.09.007