Inbreeding depression and selfing rate were investigated in the self-compatible vine Ipomoea hederacea to assess the variability of the breeding system. Seeds were collected from seven counties and thirteen populations across Alabama. The objectives of the present study used multiple populations to determine (i) the occurrence of inbreeding depression; (ii) the timing of inbreeding depression relative to plant phenology; (iii) if inbreeding differed between the greenhouse and the field; and (iv) the relative levels of genetic variation using allozyme loci.
Results/Conclusions
Plants from Macon County, Alabama, had significant inbreeding depression (31%) at germination, but no significant inbreeding depression for above ground biomass or number of reproductive structures (buds and flowers) at 45 days post germination in the greenhouse or in the field. Plants from Morgan County, Alabama, however, had significant inbreeding depression (>50%) for all three life-cycle stages in the greenhouse. Allozyme comparisons found that 5 out of the 11 I. hederacea populations surveyed had high selfing rates (66.66 – 92.53%) and high levels of homozygosity (FIS = 0.500 – 0.861) in 2003 and 3 out of 4 populations surveyed in 2004 had selfing rates that exceeded 50%. High selfing rates, high levels of homozygosity and low levels of inbreeding depression suggest that inbreeding depression may not present a significant barrier to the transmission of selfing alleles in some populations I. hederacea, but does not explain the maintenance of a mixed-mating system in other populations.
