Photosynthate and Dry Matter Partitioning in Short- and Long-Season Cotton Cultivars

Differences in source-sink relationships between short- and long-season cotton (Gossypium hirsutum L.) cultivars, the contribution of main stem leaves to boll growth, and the distribution of nonstructural carbohydrates late in the season are not well understood. This study compared the cultivars Tamcot CAMD-E (a short-season type) and Stoneville 213 (a long-season type) for two seasons in the field. To study photosynthate partitioning, the uppermost fully expanded leaf on the main stem subtending a reproductive axillary branch was pulsed with 14 CO 2 at the onset of reproductive growth (ORG) and at early reproductive growth (ERG), and sampled 48 h later. To study non-structural carbohydrate partitioning, 14 C-starch was injected into the base of the main stem just above the soil surface during late reproductive growth (LRG). At ORG in 2 yr and ERG in the year with poor growing conditions, there were no cultivar differences in partitioning of accumulated dry matter throughout the plant or recent 14 C-photosynthate. However, at ERG in a year with good growing conditions, Tamcot CAMD-E distributed a greater percentage (45%) of its dry matter to reproductive growth than did Stoneville-213 (30% ). Tamcot CAMD-E also partitioned 85% of its 14 C-photosynthate to the reproductive structures compared with only 60% in Stoneville-213. Main stem leaves were an important source of photosynthate to the developing bolls in both cultivars and years. The total nonstructural carbohydrates of the main stem and root contained from 20 to 90% of the 14 C-photosynthate from the main stem leaves partitioned to the main stem or root at ORG and ERG. Both cultivars partitioned more than one-half of the injected 14 C-starch to the main stem and its vegetative branches in both years at LRG. At this later stage of reproductive growth, cotton production could benefit from a different pattern of partitioning that favored the distribution of stored carbohydrates to reproductive structures.