PARENT SESSION
Oral Session #65: Evolutionary Ecology/ Population Genetics. Presiding: G. Gerrish.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.
Long-term persistence of crop alleles in experimental populations of a common weed, Raphanus raphanistrum.
SNOW, ALLISON1, UTHUS, KRISTEN1, CULLEY, THERESA2, 1 2
ABSTRACT- Fates of crop alleles that spread to wild populations have rarely been studied beyond the F1 generation. To examine this process in a common weed, wild radish, we created four isolated populations in Pellston, MI, in 1996. Each population was founded by 100 F1 crop-wild hybrids (R. raphanistrum x R. sativus) and 100 wild plants (R. raphanistrum), so the initial frequency of crop-derived alleles was 0.25. In subsequent years, we monitored crop alleles coding for GPI (glucophosphoisomerase), PGM (phosphoglucomutase), and white flower color (a dominant trait). From 1997-2000, population sizes ranged from <100 to >100,000 individuals. Frequencies of white-flowered plants dropped from 0.50 in 1996 to only ~0.10 in 1997 and remained relatively steady during the next three years. In contrast, crop alleles of GPI and PGM reached frequencies of up to ~0.25 by 1999. This indicates that different selective pressures may affect the persistence of flower color and the two unlinked allozymes. Low pollen and ovule fertility (>30% aborted) was observed in the 1996 F1 hybrids, which were heterozygous for a reciprocal translocation. By 1999, fewer than ~20% of the plants in each population had low pollen fertility, most likely due to selection against this deleterious trait. These results illustrate the dynamics of introgression and demonstrate that reduced fitness of F1 hybrids is not a barrier to the transfer of genes from a crop to its weedy relative.
KEY WORDS: hybrid, introgression, crop, Raphanus raphanistrum