Fruiting Efficiency in Cotton: Boll Size and Boll Set Percentage
- Johnie N. Jenkins ,
- J. C. McCarty and
- W. L. Parrott
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.
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