Partial Diallel Crosses

A diallel cross is a set of all possible matings between several genotypes, which may be individuals, clones, homozygous lines, etc. Such crosses are used to estimate general and specific combining abilities of lines and crosses respectively. For ‘n’ inbreed lines, the possible F1’s are n(n–1)/2, which are to be tested in a suitably replicated randomized design. With facilities available for testing a limited number of crosses, a diallel cross therefore will be possible only when n is relatively small. However, if only a small number of lines are included, the estimate of variances of the general and specific combining abilities among the whole population of potentially available lines are subject to large sampling errors and many potentially high yielding lines may be left completely untested. It is therefore necessary to have a large number of inbreed lines but raise only a sample of all possible crosses among them. Such a diallel cross is known as partial diallel cross (PDC). A series of designs for PDC based on different association schemes can be constructed. PDC based on Latin Square type (Li), Group-Divisible (GD) and triangular (T) association schemes with two associate classes, Factorial Design (FD), and Extended Triangular Design (ETD) both with three associate classes and Multi-Triangular Design (MTD) with four associate classes have been discussed.