THE DEGREE OF EARLY INBREEDING DEPRESSION DETERMINES THE SELFING RATEAT THE SEED STAGE - MODEL AND RESULTS FROM PINUS-SYLVESTRIS (SCOTS PINE)

Early inbreeding depression, i.e. embryonic recessive lethals, elimina tes a large proportion of selfed progeny during embryo development. A model of early inbreeding depression suggested that in most conifers t he variation between genotypes in the number of lethals rather than th e variation in the actual rate of self-fertilization accounts for the variation between selfing rates at the seed stage. Polyembryony, the f ormation of several embryos per ovule in conifers, diminished the fitn ess cost of embryonic lethals and allowed embryo competition. We studi ed variation in the outcrossing rate at the seed stage in an experimen tal population of Scots pine. Despite extensive variation, pollen prod uction of the trees, which is expected to predict the probability of s elf-fertilization, did not account for the low selfing rate variation at the seed stage. The genotypes having lowest numbers of embryonic le thals had the highest selfing rates at the seed stage. Early inbreedin g depression maintains a very low selfing rate at the seed stage and m asks the correlation between the rate of self-fertilization and the se lfing rate at the seed stage. This is typical of most conifers and can also be common among perennial angiosperm species.