The Use of Obsolete and Modern Cultivars to Examine Advances in Yield and Dry Matter Partitioning

Genetic gain through cotton improvement has been best established by testing obsolete and modern cultivars in the same environments. This review is an examination of the yield and growth analysis studies performed at Stoneville, MS in the 1970s and 80s. There were four yield studies that exhibited a mean increase of approximately 7.4 kg lint ha(-1) yr(-1) and a range from 4.8 to 10.2 kg lint ha(-1) yr(-1). The lowest value was observed at a low nitrogen rate of 22 kg N ha(-1). Growth analysis showed earlier and more intense flowering rates in the modern cultivars than rates seen in more obsolete cultivars. This maturity difference was supported by significant, negative correlation coefficients for the relationships between the year of cultivar release and various parameters of vegetative growth later in the season. These data indicate that there was greater vegetative mass in the obsolete cultivars at that time. The opposite was true of the reproductive parameters, which were positively related to year of cultivar release. Reproductive-to-vegetative (RVR) dry weight (DW) ratio was significantly related to year of cultivar release at 69, 96, 117 and 142 days after planting (DAP) with coefficients of 0.39(star), 0.50(star star), 0.61(star star) and 0.53(star star) respectively. Further work with advanced breeding lines and present day cultivars indicated that yield increases through partitioning from vegetative to reproductive structures were likely to continue. It is not known if such alterations have been brought forward in today's biotechnologically modified cultivars.