Using mixing ability analysis from two-way cultivar mixtures to predict the performance of cultivars in complex mixtures

Cultivar mixtures are an alternative to monoculture for crop production. Methods for predicting the performance of cultivars in mixtures would facilitate the identification of the best cultivars for mixture formation. A prediction method [Theor. Appl. Genet. 81 (1991) 265] based on the combining ability analysis proposed by Gardner and Eberhart [Biometrics 22 (1966) 439] model II was evaluated for mixtures. Mean values for percent diseased leaf area (DLA) and yield under disease (YUD) of five club wheat cultivars and all possible two-way mixtures (across three Oregon locations) were used to estimate the relative contribution of each cultivar to the mixture mean (I-i) and the predicted mean of all possible mixtures (Y-m) according to the MFC method. Estimated I-i and Y-m were compared to actual mixture means, I-i allowed identification of the best cultivars for mixture formation for both DLA and YUD. Actual and predicted rank correlation coefficients for DLA and YUD of complex mixtures (more than two components) were highly significant (P < 0.01) for the mean of the three environments (0.87 and 0.78, respectively) and for the mean of the two most relevant environments (0.83 and 0.93, respectively). Similar results were obtained when I-i and Y-m were estimated from the means of the cultivars in pure stand (instead of being estimated from the mixing ability analysis). This was due to the relatively small competitive effects (h(i)) of the cultivars compared to their additive effects (v(i)). We extended our analysis to data from a yield study of two-way mixtures of eight soybean cultivars [Crop Sci. 29 (1989) 885; Agron. J. 81 (1989) 559], where additive and competitive effects had similar magnitude. Actual and predicted mixture means could not be compared because only two-way mixtures were included in the study. In this case, the mean yield of the cultivars in pure stand was not a good predictor of the performance of cultivars in mixtures. Ra 604, the third highest yielding cultivar, had a positive additive effect (v(i) = 53.8 kg/ha), but a highly negative competitive effect (h(i) = -49.7 kg/ha) that resulted in a negative contribution (I-i) to yield when mixed with the other soybean cultivars. Additive (v(i)) and competitive effects (h(i)) must be considered to obtain superior mixtures, and the advantage of I-i is that it takes into account both effects (I-i = 1/2v(i) + (k - 1/k)h(i), k is the number of cultivars). The MFC method may be a useful tool to select desirable cultivars to obtain complex mixtures. (C) 2000 Elsevier Science B.V. All rights reserved.