RIPENING TIME WITHIN A CROSS-DERIVED POPULATION OF JAPANESE PLUM

Ripening time was evaluated in a seedling population of Japanese plum planted in 1990, which comprised 377 seedlings derived from 12 controlled crosses. Heritability, estimated by regressing the 12 F₁ progenies on their mid-parents, was very low (0.44), suggesting a great non-additive genetic component of variance. A high variability was observed in the distribution of offsprings compared to their respective parents, either for range of ripening time, or frequency and mode. The distribution of frequencies showed 3 different patterns: uni-, bi and tri-modal. In some cases the offspring mean and mode were almost equal to the parent mean; otherwise mode and/or mean were anticipated or postponed with respect to both parents. These results indicated that in a Japanese plum breeding programme parents should be evaluated and chosen on the base of cross performance and combining ability.