Fruiting Efficiency in Cotton: Boll Size and Boll Set Percentage

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Abstract
Cotton plants, Gossypium hirsutum L., initiate more fruiting buds than are matured. This research quantified the boll set percentage and boll size by fruiting site in a population of cotton plants. The fruiting sites of harvestable bolls were recorded for 2 yr in eight cultivars: Stoneville 213 (ST 213), Stoneville 506 (ST 506), Stoneville 825 (ST 825), Tamcot CAMD‐E (CAMD‐E), Deltapine 50 (DPL 50), McNair 235 (MC 235), DES 119, and Deltapine 20 (DPL 20). Plants were thinned to ~95 000 plants ha−1 in rows spaced 1 m apart. All cultivars behaved similarly; however, in the newer, early‐season cultivars (DPL 50, DPL 20, and DES 119), more plants retained a boll at Nodes 6 through 8 than in the older cultivar ST 213. Percentage of plants with a harvestable boll at Position 1 on a sympodial branch increased from 9.6% at Node 6 to 48.7% at Node 12, declining thereafter, and varied from 0.2 to 21.2% at Position 2. Fewer than 5% of the plants matured a boll at Position 3. Percentage of plants with a harvestable boll peaked at Nodes 11, 9, and 8 for Positions 1, 2, and 3, respectively. Assuming a 3‐d vertical flowering interval, boll size and boll set percentage began decreasing 15 to 18 d after first bloom. In 1988, fewer plants matured a harvestable boll at Nodes 9 through 12 than in 1987. This was attributed to reduced solar radiation, lower temperatures, and more daytime rainfall events during July. Bolls at Position 1 were 14 and 21% larger than those at Positions 2 and 3, respectively. Boll size followed a pattern similar to percent of plants with a harvestable boll. Partitioning of photosynthate to older bolls resulted in fewer mature bolls at Positions 2 and 3 for all nodes. Smaller bolls had fewer and smaller seed. This information on plant fruiting by positions and nodes can guide breeders in selection for earlier‐ and higher‐yielding cultivars.