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PLANT GENETIC RESOURCES

Inflorescence Sampling Improves Effective Population Size of Grasses

Dep. of Statistics, Washington State Univ., Pullman, WA 99164-6402

^* Corresponding author (rcjohnson{at}wsu.edu).

Variation in seed production per plant leads to reductions in effective population size (N_e), which is a major factor promoting genetic drift of heterogenetic populations during seed collection and regeneration. The objectives of this study were (i) to compare N_e to the census population size (N_c) among different seed harvest methods; (ii) use inflorescence sampling to determine N_e/N_c for numerous heterogenetic grass species, and (iii) to predict the optimum number of inflorescences per plant to most efficiently increase N_e. Estimates of N_e/N_c from rubbing whole plants, cutting whole plants, and from sampling a constant two inflorescences per plant were made on Festuca pratensis Huds., Lolium perenne L., and Pseudoroegneria spicata (Pursh) Á. Löve accessions. Inflorescence sampling was also completed on four accessions of Bromus inermis Leyss., Dactylis glomerata L., F. arundinacea Schreb., L. perenne, Pseudoroegneria spicata, and Phalaris aquatica L. The mean N_e/N_c for the inflorescence method was 0.78, significantly higher then the 0.64 average for the cut or rub methods. For all species and entries, the slope of the curves describing N_e/N_c to inflorescence number was initially steep from 1 to 3 inflorescences and then leveled off asymptotically. Thus, most of the benefit occurs after sampling only a few inflorescences. The results show that sampling a constant number of inflorescences per plant promotes N_e and reduces the potential for genetic drift associated with collection and regeneration of heterogenetic grass populations.

Abbreviations: N_c, census population size • N_e, effective population size

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THIS ISSUE IN CROP SCIENCE

Crop Science 2004 44: 1109-1112. [Full Text]