Photosynthate and dry matter partitioning in short- and long-season cottoncultivars

Differences in source-sink relationships between short- and long-season cot ton (gossypium hirsutum L,) cultivars, the contribution of main stem leaves to boil growth, and the distribution of nonstructural carbohydrates late i n the season are not well understood. This study compared the cultivars Tam cot CAMD-E (a short-season type) and Stoneville 213 (a long-season type) fo r two seasons in the field. To study photosynthate partitioning, the upperm ost fully expanded leaf on the main stem subtending a reproductive axillary branch was pulsed with (CO2)-C-14 at the onset of reproductive growth (ORG ) and at early reproductive growth (ERG), and sampled 48 h later. To study nonstructural carbohydrate partitioning, C-14-starch was injected into the base of the main stem just above the soil surface during late reproductive growth (LRG), At ORG in 2 gr and ERG in the year with poor growing conditio ns, there were no cultivar differences in partitioning of accumulated dry m atter throughout the plant or recent C-14-photosynthate. However, at ERG in a year with good growing conditions, Tamcot CAMD-E distributed a greater p ercentage (45%) of its dry matter to reproductive growth than did Stonevill e-213 (30%). Tamcot CAMD-E also partitioned 85% of its C-14-photosynthate t o the reproductive ce structures compared with only 60% in Stoneville-213. Main stem leaves were an important source of photosynthate to the developin g boils in both cultivars and years. The total nonstructural carbohydrates of the main stein and root contained from 20 to 90% of the C-14-photosyntha te from the main stem leaves partitioned to the main stem or root at ORG an d ERG. Both cultivars partitioned more than one-half of the injected C-14-s tarch to the main stem and its vegetative branches in bath gears at LRG, At this later stage of reproductive growth, cotton production could benefit f rom a different pattern of partitioning that favored the distribution of st ored carbohydrates to reproductive structures.