ESTIMATION OF THE COMPONENTS OF THE GENETIC VARIANCE OF A SYNTHETIC FROM NON-INBRED AND UNRELATED PARENTS

Abstract

Synthetics (VS) are stable and Iow-input cultivars which allow the production of their seed in a Iow-cost and efficient way. Besides, a VS may also be subjected to genetic improvement to develop a superior variety. To achieve this, a strategy according to the structure of genetic variability of the VS should be used. Thus the components of the genetic variance (GV) of the VS must be estimated in advance. This is why the components of the GV of the VS have to be identified. In this study the composition of the GV of a VS was determined and for each of its components an estimator was derived. For the additive and dominance variances the estimators were those corresponding to a design II of North Carolina which is formed by crosses among the parents, in this case considered as noninbred, unrelated, and each represented by a single plant. For the square of the mean of the homozygous dominance deviations of the genotypes with alleles which are identical by descent (S_ii) the estimator was 4[R-CME/_nr], where R is the experimental mean of the n families formed by selfing each parent; CME is the error mean square and r is the number of replicates. Estimators of the variance of the S_ii and of the covariance between S_ii and the effects of the corresponding alleles (αi) were derived from two equations: one for the variance of the means of the families generated by selfing each cross between two parents and the second for the covariance between these means and the mean of the progenies obtained by selfing the parents.