Comportement en croisement des haploïdes doublés de cacaoyers (Theobroma cacao)

Abstract

The crossing value of double haploids (DH) of cacao has been studied for vegetative characters 1 or 3 months after sowing and a 1.5 year after planting, as well as for quantitative characters observed on the first two harvests. Families arising from DH × heterozygote crosses have been compared to crosses between the original parents of the DH and the same heterozygous parents. When the families came from reciprocal crosses the existence of reciprocal effects was observed. Except for the first stages of observation, DH with a higher crossing value than that of their parents have been found. The fact that the behaviour of the original parents is relatively similar to that of the DH they give rise to, justifies the assumption that classical selection might be useful in the search for good parental DH. With regard to the choice of the direction of the cross, the female HD parents seem to be unfavourable only for those vegetative characters linked to the earliest stages. This effect later disappears. For initial yields, the structure of the homozygous or heterozygous parent does not seem to influence the within-family variances, and families arising from DH × DH crosses are as heterogeneous as those obtained from crosses between two heterozygous parents. Thus, the homogenization of the offsprings through the use of DH will only be effective for characters which are very stable in the habitat.