Genetic Structure of Natural Populations of Wild Sunflowers (Helianthus annuus L.) in Australia

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Abstract
The genetic structure of 11 wild populations of H. annuus occurring in New South Wales and Queensland was determined by isozyme analysis. Considerable isozyme diversity was found among loci within and between populations with three to five alleles being identified at each of 10 loci. Mean levels of heterozygosity ranged from 0.19 to 0.38 and gene diversity values from 0.29 to 0.52. In all populations Wright''s fixation indices were positive (0.09-0.51) suggesting a degree of inbreeding. Differences in the level of genetic differentiation between populations were not correlated with geographic distance. Indeed, notable genetic diversity was detected between six sites occurring within a 2-km radius of Gunnedah, N.S.W., where the genetic distance relationships were D = 0.13 .+-. 0.08, the same as those between populations throughout the region. There was statistically significant heterogeneity in gene frequency differences between alleles among populations at all loci (115 < .chi.2 < 254, d.f. = 30, P < 0.001). The significant diversity found in these populations suggests that there is considerable scope to utilize wild H. annuus in the improvement of commercial sunflowers.