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Heterosis and Inheritance of Quantitative Characters in Interspecific Crosses of Cotton¹

Performance of the F₁, F₂ and backcross generations of nine interspecific crosses, between each of three varieties of Gossypium hirsutum L. (‘Acala 4-42’, ‘Empire W,’ and ‘Coker 100A’) and each of three varieties of G. barbadense L. (‘Karnak,’ ‘Malaki,’ and ‘Giza 7’), in comparison with the parental varieties, was evaluated in three field trials in 1964 and 1965. Heterosis (F₁ performance above mean of parents) was between 52% and 73% for lint yield and was associated with heterosis for boll number, flower number, and percentage of boll retention. Boll weight of F₁ hybrids was intermediate and their lint percent and number of seeds per boll were lower than the parental mean. Heterosis was also significant for seed index, lint index and plant height.

F₂ deviation (F₂ performance below mean of F₁ and midparent) and backcross deviations (BC performance below mean of F₁ and recurrent parent) were significant for almost all of the characters examined. Lint yield of the F₂ was much lower than that of either parent, whereas lint yield of backcrosses was similar to that of the recurrent parents. Heterosis was caused by dominance effects only (no epistasis) for seed index and in one trial for final plant height. Heterosis for yield of seed cotton, yield of lint, boll number, flower number, percentage of boll retention, lint index and plant height at flowering was caused by dominance in the presence of epistasis. Intermediate F₁ performance (no heterosis), found for boll weight and for maturity, was caused by the estimates of dominance and additive x additive epistasis parameters being of nearly equal magnitudes. The negative heterosis found for lint percent and number of seeds per boll was caused by the additive x additive epistasis being larger than the dominance effects.

Key Words: Gosspium • genetic parameters • backcrosses

² Senior Lecturer, Department of Field and Vegetable Crops.

Received for publication October 3, 1967.