Abstract

In 1974, a district cotton cultivar trial was initiated to assess the yield and fibre quality of promising cultivars in all major Australian cotton growing areas over 1 or more years. A nearly 5-fold range in site yields (595-2451 kg/ha) occurred across locations and years. Yields were usually higher in the last 6 years of the trial (overall mean 1688 kg/ha) than in the first half (overall mean 1223 kg/ha). Queensland sites (except Theodore) were lower yielding than average, while New South Wales sites (except Warren) were higher yielding. Deltapine cultivars from the U.S.A. have been the dominant commercial cultivars during 1974-85, and in the first 9 years of the trials USA. or Australian-bred Deltapine types produced the highest overall lint yields. Since 1982, Australian-bred Siokra lines have been the highest yielding with their resistance to bacterial blight apparently being an important factor in their performance. The rate of genetic gain in lint yield, as assessed from the overall year means and the mean yield of the 2 control cultivars (Deltapine 16 and Namcala) grown in all 12 years of the trials, was 2.3% per year. These yield increases were also accompanied by improvements in fibre strength and micronaire value in some of the recently developed lines or cultivars. A number of genotypes with mutant traits associated with host plant resistance to insect pests were compared with their near-isogenic counterparts. Superokra leaf yielded 6% less than normal leaf, nectariless yielded similarly to nectaried, and glabrous yielded similarly to delta-smooth pubescence. Frego bract yielded less in 1 comparison but in 2 others was similar to the normal counterpart, while glabrous and frego bract together led to reduced yields. Intra-varietal selection was shown to produce useful gains in yield between 3 to 6.5%.