Trends over Time among Cotton Cultivars Released by the Oklahoma Agricultural Experiment Station

Abstract

Twelve cotton (Gossypium hirsutum L.) cultivars, released by the Oklahoma Agricultural Experiment Station (OAES) between 1918 and 1982 inclusive, were evaluated in multiple environments to estimate selection progress over time for lint yield, six fiber properties, eight agronomic characters, and three diseases. Lint yield increased 1.2 to 3.0 kg ha−1 yr−1 on dryland and 3.7 to 5.6 kg under irrigation. Five of six experiments indicated that a selection plateau had not yet been reached for lint yield. Increases in fiber length of 0.04 to 0.06 mm yr−1 and of 0.02 mm yr−1 were observed for 2.5 and 50% span lengths, respectively. Uniformity index and micronaire displayed significant differences among cultivars, but no significant trends over time. T0 fiber strength increased by 0.5 kN m kg−1 yr−1 Initially, T1 fiber strength declined; but since the mid‐1940s, its trend was upward by 0.6 kN m kg−1 yr−1 in a generally linear fashion. Picked and pulled lint percentages increased rapidly at first but reached a plateau in the mid‐1940s. Boll size increased over time, and bur size increased slightly. Weight of lint per boll increased through 1955, but has since remained essentially constant. Relatively large improvements were made in lint index through 1964; but since then, the trait has remained stable. Seed index increased by 0.02 g (100 seed)−1 yr−1 on dryland and by 0.03 g under irrigation. Lock tenacity increased by 1.7 g force yr−1 Positive trends over time were also noted for resistance to bacterial blight [caused by Xanthomonas campestris pv. malvacearum (Smith) Dye] and to the Fusarium wilt [caused by Fusarium oxysporum Schlect. f. sp. vasinfectum (Atk.) Snyd. & Hans.]–root‐knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] complex but not for tolerance to Verticillium wilt (caused by Verticillium dahliae Kleb.). The above findings were compared with those in numerous other breeding programs. This information provides a historical perspective on genetic gain for a number of traits among the cotton cultivars released by the OAES.