Using mixing ability analysis from two-way cultivar mixtures to predict the performance of cultivars in complex mixtures Cesar G. Lopez a,b,* , Christopher C. Mundt c a Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97331-2902, USA b Catedra de Mejoramiento Vegetal, Facultad de Ciencias Agrarias, Universidad Nacional de Lomas de Zamora, Argentina c Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331-2902, USA Received 10 March 2000; received in revised form 11 July 2000; accepted 17 July 2000 Abstract Cultivar mixtures are an alternative to monoculture for crop production. Methods for predicting the performance of cultivars in mixtures would facilitate the identi®cation 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 ®ve 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 identi®cation of the best cultivars for mixture formation for both DLA and YUD. Actual and predicted rank correlation coef®cients for DLA and YUD of complex mixtures (more than two components) were highly signi®cant (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 2 v 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. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Cultivar mixtures; Combining ability analysis; Mixing ability analysis 1. Introduction Multilines and cultivar mixtures are alternatives to monoculture for crop production. Although both alter- natives can be used, cultivar mixtures have received Field Crops Research 68 (2000) 121±132 * Corresponding author. Address: Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97331-2902, USA. Tel.: 1-541-737-5876; fax: 1-541-737-0909. E-mail address: lopezc@css.orst.edu (C.G. Lopez). 0378-4290/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII:S0378-4290(00)00114-3