Weighted regression analysis for comparing varietal adaptation

The normally used joint linear regression analysis (OLS) is not appropriate for comparing estimates of stability parameters of varieties when the error variances of site means are heterogeneous. Weighted regression analysis (WLS), in these situations, yields more precise estimates of stability parameters. A comparison of the two analytical methods using the grain yield (kg ha(-1)) data of 12 varieties and one hybrid of pearl millet [Pennisetum typhoides (Burm.) S. & H.], tested at 26 sites in India, revealed that the weighted regression analysis yields more efficient estimates of regression coefficients (b i ) than the ordinary regression analysis, and that the standard errors of b i values were reduced by up to 43%. The estimated b i differed with the two procedures. The number of varieties with b i ssignificantly deviating from unity was not only more (five varieties) with weighted regression analysis than the ordinary regression analysis (one variety), but the classification of varieties as possessing general or specific adaptation differed with the two procedures.

Regression analysis for general adaptation in pearl millet using different environmental indices

Regression analyses on grain yield of 20 hybrid and 13 composite varieties of pearl millet (Pennisetum typhoides (Burm. S. & H.)) evaluated at 19 sites in India were performed to assess their relative stability and to compare different measures of environmental values. A large portion of the significant genotype X environment interactions was attributed to the non-linear component and deviations mean squares (Sdi (2)) were a very important parameter for selection of stable varieties. The mean grain yield was positively associated with regression coefficients and deviations mean squares. The hybrids MH 31, MH 35, MH 36 and MH 62 and composite populations MP 16, MP 31 and MP 36 possessed general adaptability. The use of dependent, independent and near-independent measures of environmental values has been found to have little influence on the general interpretation of regression analysis in pearl millet.