Population genetics of colonizing success of weedy rye in Northern California

Genetic parameters of 11 weedy rye populations located in California's northern mountain area and the adjoining Oregon border were compared with those of the putative parents, wild species Secale montamim and cultivated rye S. cereale. All weedy populations exhibited high levels of genetic variation as determined by isozyme analysis. On average, 44% of the isozyme loci were polymorphic, total genetic diversity was 0.30; and number of alleles per locus was 1.65. High genetic identities, averaging 0.994 ± 0.005 between populations, indicated that little genetic differentiation has occurred among these weedy populations since the initial colonization. Lack of population differentiation could be attributed to a wind-pollinated, self-incompatible breeding system resulting in extensive gene flow among weedy populations, and between weedy populations and local cultivars of rye. Multilocus outcrossing rates of weedy populations ranged from 0.86 to 0.97. The estimated levels of gene flow using the private-alleles method were high among weedy populations, and between cv 'Merced' and weedy populations, with estimated Nm values of 14.50 and 8.21, respectively. The colonizing success of weedy rye is discussed and a strategy for its conservation recommended.