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Acala‐type cottons (Gossypium hirsutum L.) released from New Mexico have contributed significantly to the development of commercial upland cultivars in the United States. The objective of this study was to assess the genetic gain in the breeding program between 1926 and 2000 through a combined analysis of field data on representative Acala cultivars from New Mexico and California obtained in multiple tests over years. From 1926 (‘Acala Original’) to 2000 (‘Acala 1517‐99’), the overall lint yield improvement was estimated at 3.2 kg ha−1 yr−1 but was 6.4 kg ha−1 yr−1 in 1926 to 1970 and 10.2 kg ha−1 yr−1 in 1975 to 2000. The yield improvement was accompanied by an increase in lint percentage (from 37 to 40%), fiber strength (from 270 to 300 kN m−1 kg−1), and micronaire, but with reduced boll weight. Although there was an upward trend for fiber length and uniformity and a downward trend for short fiber content, the three traits remain stable. Comparing eight New Mexico Acala 1517 cultivars with nine California Acala cultivars bred during the same period (late 1930s to the 1970s), the former, as a group, had longer and stronger fibers but slightly lower lint percentage and elongation. The Acala 1517 cotton cultivars provide an excellent source of parental lines for developing cotton cultivars with enhanced fiber quality.

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