Abstract:

Reduced seed yields after self-pollination are generally thought to be induced by early-acting inbreeding depression and self-incompatibility. Early-acting inbreeding depression occurs strictly post-zygoti- cally, and leads to the abortion of progeny that are homozygous for deleterious recessive alleles at an early stage of seed maturation. Late-acting ovarian self-incompatibility, on the other hand, may be either pre- or post-zygotic, and usually only one locus is responsible for the rejection. In the pre-zygotic late-acting self-incompatibility, the selfed pollen tube may grow to the ovary or penetrate the ovule, but cannot fertilize the ovule. Post-zygotic self-incompatibility, referred to as an abortion, occurs shortly after fertilization, and is a result of the interaction between the maternal plant and the zygotes. Based on differences between these two phenomena, eight methods have been proposed to distinguish between them. Three of them are used to identify the timing of the abortion, pre- or post-zygotic, including anatomical observation, comparison between the seed set following self-pollination and chase-pollination, and using linear regression models to test whether the sum of mature and aborted seeds remains constant. The key to distinguishing post-zygotic self-incompatibility from early-acting inbreeding depression is to judge whether the reduction in seed yield after self-pollination is controlled by a single locus or the expression of deleterious alleles involving multiple loci, or to focus on the phenotypes associated with these two genetic basis.

Key words: early-acting inbreeding depression, late-acting self-incompatibility, pre-zygotic, post-zygotic, genetic load