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Genotype x Environment Interactions for Cane and Sugar Yield and Their Implications in Sugarcane Breeding¹

Genotype x environment (GE) interactions limit the effectiveness of selection when selection is based only on mean yields. This study evaluated three methods of partitioning GE interaction into stability-variance components assignable to each cultivar in sugarcane (Saccharum spp.) cultivar evaluation tests. An unbiased stability-variance parameter (²₁) developed by Shukla and an ecovalence stability index (w) developed by Wricke were calculated separately for plant-cane and ratoon crops for Brix (%), grams of sugar per kilogram of cane, and tons per hectare of cane and of sugar for 11 cultivars. A cultivar x location component of variance (²_c1) proposed by Plaisted and Peterson was also calculated. Within each crop, ²₁ and w had identical cultivar rankings (r_s = 1.00**) (**, Significant at the 0.01 level.) for each of the four traits studied. We propose that w sum of squares for each cultivar be expressed as w mean square and the latter be tested for significance in the same manner as ²₁. Those cultivars with a significant mean square were judged to be unstable. Shukla's method allowed use of a covariate of fertility and cultural practices at different locations to remove heterogeneity variance (nonadditivity) from the GE interaction, and partitioning of the remainder of variance assignable to each cultivar (²₁). Certain cultivars were judged stable after the covariate adjustment, indicating that the instability Was introduced by the linear effect of the covariate. Methodology for computing the ²_CL component is cumbersome and would have little application when a large number of genotypes are evaluated. Repeatability of stability-variance parameters between crops (individual repeatability) was relatively low for the four traits studied.

Key Words: Saccharum spp. • Ecovalence • Stability-variance parameters • Adaptation • Cultivar testing

² Assistant professor, Univ. of Florida, Agric. Res. and Educ. Ctr., Belle Glade, FL 33430 and research geneticist, USDA/ARS/SR, Sugarcane Field Stn., Canal Point, FL 33438, respectively.

Received for publication April 4, 1983.