Response to Inbreeding of Seedling Traits in a Prunus domestica L. Breeding Population

Abstract

Controlled pollinations were made using 20 elite selections from the University of California, Davis, Prunus domestica (european plum) breeding program as parents. These parents were used to generate 11 self-pollinated progenies with an inbreeding coefficient (F) of 0.5, 10 full-sibling progenies (F = 0.25), and 11 progenies from among nonrelated parents (F = 0). Seven additional progenies were chosen as a random-mating control set within the parental group; progenies in the control set had accumulated a range of current inbreeding coefficients (average F = 0.23) over two to five generations with intervening cycles of selection. Survival percentages were 85, 82, and 74 for the full-sib progeny, control set progeny, and selfed progeny, respectively, relative to nonrelated progeny. Two months after germination the percent decrease in the growth trait means for the selfed progeny compared to the nonrelated progeny ranged from 14% to 30% whereas growth trait means for full-sib progeny decreased from 1% to 9% compared to nonrelated progeny. The percent decrease for growth trait means of the selfed progeny after completing one season of growth in the field (10 months) was similar to that observed after 2 months, ranging from 14% to 28% compared to nonrelated progeny, whereas the decrease in full-sib progeny trait means was somewhat greater, ranging from 6% to 20%. Regression analysis of all growth traits on current-generation rates of inbreeding indicated a significant negative linear relationship (P = 0.0011 to 0.0232). No significant relationships were found between accumulated Fs and growth trait means of the control set progenies and the nonrelated progenies after 2 months in the greenhouse or one season growing in the field, suggesting that selection between breeding cycles decreased inbreeding depression.