The magnitude and consistency of midparent (MP) and high parent (HP) heterosis over locations and/or years were studied for cotton (Gossypium hirsutum L.) lint yield, two lint percents, and five fiber properties. Due to limited time, only the lint yield data were discussed in this presentation. The parents, F₁s, and F₂s were evaluated for all possible crosses, ignoring reciprocals, among five Plains-type cultivars [(l) 'Lockett 77', (2) 'Tamcot SP21', (3) 'Paymaster 303', (4) 'Tamcot SP371', and (5) 'Westburn M']. Replicated split-plot experiments were conducted at Perkins, Chickasha, and Tipton, OK, under irrigation in 1977, 1978, and 1979.

Six parental combinations (1 X 3, 1 X 4, 1 X 5, 2 X 4, 3 X 5, and 4 X 5) displayed significant F(l) MP heterosis for lint yield ranging from 11.5 to 34.0%. That heterosis was consistent over locations and years. The four other combinations sporadically displayed significant F₁ MP heterosis over locations, over years, or both. Five parental combinations (1 X 3, 1 X 4, 1 X 5, 3 X 4, and 3 X 5) exhibited significant F₁ HP heterosis for lint yield ranging from 12.6 to 26.6%. That heterosis was consistent over locations and years. Those five combinations have economic potential. One of the remaining combinations (2 X 3) did not exhibit significant Fl HP heterosis. The four remaining combinations sporadically exhibited significant F₁ HP heterosis over locations, over years, or both. Their economic potential is questionable.