Diversity of Washoe pine and comparisons with allozymes of ponderosa pine races

Washoe pine (Pinuswashoensis Mason and Stockwell), a narrow endemic native to mountains on the western rim of the Great Basin in northeastern California and northwestern Nevada, may be on the verge of extinction. Lowered genetic diversity and increased interpopulation differentiation are expected evolutionary consequences for small, isolated populations like those of Washoe pine. But the species has levels of allozyme variation (estimated average heterozygosity for 26 loci equals 0.148) similar to those for widespread geographic races of ponderosa pine (Pinusponderosa Laws.), which are likely to be its closest extant relatives. Heterozygosity in ponderosa pine was 0.144 in the Pacific race, 0.178 in the North Plateau race, and 0.164 in the Rocky Mountain race. Electrophoretic analysis of trees in the three well-documented populations of Washoe pine revealed only minor and nonsignificant population to population differentiation (98.4% of allozyme variation was among samples within populations). Pair-wise genetic distances between the Washoe populations and the three northern races of ponderosa pine indicated that its closest similarity was with the North Plateau race (Nei's unbiased genetic distance averaged 0.004); the next closest similarity was with samples of the Pacific race (genetic distance 0.013). Washoe pine and the Pacific and North Plateau races of ponderosa pine were all strongly differentiated from the Rocky Mountain race of ponderosa pine (genetic distances were 0.066, 0.082, and 0.060, respectively. The few remaining populations of Washoe pine may be a potentially valuable gene source for the yellow pines of North America.