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.

The effect of competition on the fitness of hybrid and BC₁ progeny of wild and cultivated radish, (Raphanus raphanistrum x R. sativus).

Uthus, Kristen¹, Snow, Allison¹, ¹

ABSTRACT- Like many closely related crop-wild pairs, wild and cultivated radish can hybridize and produce fertile F₁ offspring. Because most studies of F₁ fitness have involved potted plants, little is known about how hybrid progeny fare under field conditions. To examine this, we planted wild, F₁, and BC₁ radish seeds in a rototilled fallow field in Michigan under two growing conditions: with and without competition from newly emerging weed seedlings. Fitness components were generally lower with competition, but this treatment did not significantly affect survival, fecundity, or the relative performance of each cross type. Germination ranged from 77-89% and was significantly different among cross types (BC₁>F₁>wild). Mortality differed significantly among cross types and was greatest in BC1 plants (65% died). F₁ plants flowered latest and produced significantly fewer flowers, fruits, and seeds than wild or BC₁ plants (seed production: wild>BC₁>F₁). The multiplicative fitness of F₁ plants was 0.07 relative to wild plants, while that of BC₁ was 0.56. These results indicate that while hybrid plants had greater mortality and produced fewer seeds than wild plants, they were capable of ecologically significant levels of reproduction despite competition from other naturally occurring weeds. BC₁ plants also exhibited a fitness disadvantage, but to a lesser extent than F₁ plants, as expected. This study suggests that hybridization between crop and wild radish could lead to long-term introgression of crop alleles into wild radish populations.

KEY WORDS: Raphanus, hybridization, competition, fitness