Comparative Growth of Obsolete and Modern Cotton Cultivars. I. Vegetative Dry Matter Partitioning1

Abstract

Lint yields of cotton (Gossypium hirsutum L.) cultivars have increased consistently in this century due to breeding selection for lint production. Little is known concerning what differences in vegetative growth and development have occurred as a result. The objective of this study was to ascertain what differences in vegetative growth have occurred as a result of selection for increased yield. Twelve cultivars, six from the Stoneville, and six from the Deltapine lineage, were planted on 26 Apr. or 12 May 1982. Growth was monitored at various times during the season via leaf dry weights (LDW), stem dry weights (SDW), specific leaf weights (SLW), and leaf area indexes (LAI). In addition, light interception characteristics of the canopies were determined at 59 and 78 days after planting (DAP). Planting date did not affect the relationships found among the cultivars. Old cultivars (released before 1920) partitioned more dry matter into stems while displaying similar peak quantities of LDW. Leaf area index and light interception values indicate that many of the cultivars produced more leaf area than that required for complete light capture. Net assimilation rates (NAR) were not higher in the newer cultivars, indicating the absence of increased assimilatory capacity per unit leaf area. Negative correlations of vegetative parameters beyond 96 DAP to year of cultivar release suggest that modern cultivars make an earlier transition from vegetative to reproductive growth and may have a better coordination of assimilatory capacity with reproductive sink activity.