Combining Ability for Yield Characteristics and Earliness of Pink Bollworm-Resistant Cotton
Some germplasm lines of cotton, Gossypium hinutum L., that show resistance to pink bollworm (PBW), Pectinophora gossypiella (Saunders), also carry agronomic properties that could enhance derived germplasm. The objectives of this study were to determine (i) the agronomic performance of four germplasm lines having resistance to PBW, one having susceptibility, and the check cultivar, Stoneville 825 (ST 825); (ii) combining ability for lint yield, yield components, and earliness; (iii) F1 hybrid performance; (iv) the relative contributions of yield components to yield. Half-diallel analysis of the six parents and their 15 F1 hybrids, grown at Maricopa, AZ, for 2 yr, revealed significant year, general combining ability (GCA), and specific combining ability (SCA) effects for lint yield and bolls per plant, seeds per boll, lint weight per seed, and earliness (cumulative lint yield, as a percentage of total yield at the third of five harvests). Year ✕ GCA and year ✕ SCA were significant only for lint weight per seed. Only T39C-1-L-RES (a PBW-resistant germplasm line) equalled ST 825 in lint yield per plant, but it was later in maturity; both showed GCA effects for high yield and number of bolls. Stoneville 825 achieved its high yield by producing many relativeiy small bolls, while T39C-1-L-RES produced fewer but larger bolls. The T39C-1-L-RES ✕ ST 825 F1 showed SCA effects for high yield, seeds per boll, and earliness. This F, yielded 11% more total lint than ST 825 by countering 13% fewer bolls per plant with 25% more seeds per boll. It was also earlier than ST 825: it yielded 18% more lint by third harvest.
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