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Interactions between various genotypes were studied in four varieties of barley, four varieties of wheat, and eight barley genotypes which had survived up to 18 generations of mutual selection in a heterogeneous population. The results showed that first-order interactions between genotypes from the heterogeneous barley population were much larger than those between the varieties of wheat and barley. Natural selection therefore appears to preserve genotypes which interact synergistically. Deterministic and stochastic simulations predicted fixation of the variety with the highest pure-stand reproductive value in populations of the wheat and barley varieties. However, they predicted the development of stable multigenotypic associations in populations formed from the eight genotypes isolated from the heterogeneous barley population. The effect of random variation in the reproductive values was to decrease the time to fixation when there was no stable nontrivial equilibrium; however, when such an equilibrium existed, stochastic variation increased genetic diversity. The significance of intergenotypic interactions in maintaining genetic diversity was discussed.
Allard et al. (Sat,) studied this question.