Backcross Breeding to Increase Fiber Strength of Cotton 1

Three cycles of backcross breeding to increase fiber strength (T 1 ) of cotton ( Gossypium hirsutum L.) were studied at Stoneville, Miss. The objective was to measure the effectiveness of the backcross procedure for maintaining an adequate level of T 1 and producing desirable combinations of yield and T 1 . The source of greater T 1 was FTA 263‐20 (FTA) and the recurrent parent was ‘Deltapine 16’ (DPL 16). In each cycle, 480 F 2 plants were grown. In both BC 1 F 2 and BC 2 F 2 , 24 plants were selected. In BC 1 F 3 and BC 2 F 3 , 12 and four progeny respectively, were used to initiate the next cycle. From each of the four families descending from the four selected BC 2 F 3 progenies, 12 of 120 BC 3 F 2 plants were selected. In 1974, four sets of families were grown at two locations with two replications each. In each replication of each set, two entries of DPL 16, FTA, and BC 1 F 5 and BC 2 F 4 parents, and one entry of each of the 12 BC 3 F 3 progenies were evaluated for lint yield, yield components, and fiber properties. Mean T 1 's for DPL 16, FTA, BC 1 F 5 , BC 2 F 4 , and BC 3 F 3 were 193, 230, 220, 211, and 216, respectively. Therefore, a satisfactory level of T 1 was maintained by the backcross procedure. Assuming yield and T 1 were uncorrelated, the observed average line yield of BC 3 F 3 was 9.8% less than expected. The decrease in expected yield was partially caused by a lower than expected lint percentage. Significant variability in lint yield was detected among the four sets. The family with highest yield was only 5.3% less than expected and also had above average T 1 (T 1 = 217). These results suggest moderate success in developing desirable combinations of yield and T 1 by the backcross procedure.