DELETERIOUS MUTATION ACCUMULATION AND THE REGENERATION OF GENETIC-RESOURCES

The accumulation of mildly deleterious mutations accompanying recurren t regeneration of plant germ plasm was modeled under regeneration cond itions characterized by different amounts of selection and genetic dri ft. Under some regeneration conditions (sample sizes greater than or e qual to 75 individuals and bulk harvesting of seed) mutation accumulat ion was negligible, but under others (sample sizes <75 individuals or equalization of seed production by individual plants) mutation numbers per genome increased significantly during 25-50 cycles of regeneratio n. When mutations also are assumed to occur (at elevated rates) during seed storage, significant mutation accumulation and fitness decline o ccurred in 10 or fewer cycles of regeneration regardless of the regene ration conditions. Calculations also were performed to determine the n umbers of deleterious mutations introduced and remaining in the genome of an existing variety after hybridization with a genetic resource an d subsequent backcrossing. The results suggest that mutation accumulat ion has the potential to reduce the viability of materials held in ger m plasm collections and to offset gains expected by the introduction o f particular genes of interest from genetic resources.