Deleterious mutation accumulation and the regeneration of genetic resources

Abstract

The accumulation of mildly deleterious mutations accompanying recurrent regeneration of plant germ plasm was modeled under regeneration conditions characterized by different amounts of selection and genetic drift. Under some regeneration conditions (sample sizes >/=75 individuals and bulk harvesting of seed) mutation accumulation 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 regeneration. When mutations also are assumed to occur (at elevated rates) during seed storage, significant mutation accumulation and fitness decline occurred in 10 or fewer cycles of regeneration regardless of the regeneration conditions. Calculations also were performed to determine the numbers of deleterious mutations introduced and remaining in the genome of an existing variety after hybridization with a genetic resource and subsequent backcrossing. The results suggest that mutation accumulation has the potential to reduce the viability of materials held in germ plasm collections and to offset gains expected by the introduction of particular genes of interest from genetic resources.

Figure 1

Mutation accumulation and fitness decline accompanying recurrent regeneration of germ plasm in an outcrossing plant species, with U = 1, h = 0.35, and s = 0.05. (A) Under bulk seed harvesting. Solid lines show results for deterministic analyses; dashed lines for simulation (K = 25 only). (B) Under equal seed harvesting. Dashed and solid lines as above. (C) Fitness decline relative to initial collection. Solid and dashed lines indicate bulk and equal harvesting, respectively.

Figure 2

Mutation accumulation during recurrent regeneration of a self-fertilizing plant species. See Fig. 1 legend for details (simulation results not shown).

Figure 3

Mutation accumulation and fitness decline accompanying recurrent regeneration of germ plasm, with U = 5, h = 0.35, and s = 0.05. K = 50 parents for all results shown. (A) Accumulation of heterozygous and homozygous mutations in an outcrossing species. (B) Accumulation of homozygous mutations in a self-fertilizing species. (C) Fitness decline relative to initial collection in an outcrossing species. (D) Fitness decline relative to initial collection in a self-fertilizing species. Solid and dashed lines indicate bulk and equal harvesting, respectively.