The predictive value of quantitative genetic parameters in autogamous crops: Bias caused by intergenotypic competition. 1. F_∞-mean

Summary

Quantitative genetic theory for autogamous crops enables the estimation of the parameters m (F_∞-mean) and D (F_∞-variance) in the F₃-generation. With these estimated m and D a prediction can be made of the probability of finding superior inbred lines in the F_∞-offspring of the cross. The accuracy of this procedure is influenced by the correctness of the genetic model, by the magnitude of the error variance, and by the bias caused by intergenotypic competition, which is present in the environment in which the F₃ is grown and absent in the monoculture environment at which the selection is aimed, especially in a cereal crop like wheat. The influence of the intergenotypic competition was investigated by a special method of simulating segregating populations. In this method genotypes in the offspring of a cross are represented by varieties and segregating populations are composed by mixing the appropriate varieties according to the proper segregation frequencies. Growing the simulated population enables the estimation of m and D in the normal selection environment, while simultaneously growing the varieties in a large monoculture trial enables the calculation of ‘true’ values of m and D in the monoculture environment. Hence, a comparison is possible.

The first of this set of two papers presents the investigations on the influence of intergenotypic competition on the estimation of the parameter m. The correlation coefficient of the estimates from the selection environment with the calculated ‘true’ values from the monoculture environment was small. Sometimes the selection environment estimation significantly underestimated the (true) monoculture value of m, sometimes it significantly overestimated the monoculture value. On the average the smaller true values of m were underestimated and the larger ones overestimated.