The Cipres de la Cordillera (Austrocedrus chilensis (D. Don) Florin and Boutelje) is one of the most important tree species of the Patagonian Andean forests. In Argentina, it occupies the Andean Mountain range and foothills of Northern Patagonia, where it resides in zones of average annual precipitation ranging from 2500 mm in the high mountains of the west to 300 mm in the arid eastern steppe. Due to overexploitation, fires, root disease and livestock grazing, this species has lost and is still loosing genetic variation.
To test the existence of genetic differentiation across this remarkable east-west rainfall gradient, we chose two transects from which three and four stands, respectively, with large differences in average annual rainfall, were selected for sampling. The total collection consists of seed from 75 mother trees: 5 to 17 in each stand.
The presence of six previously identified loci coding variants of GOT-1, GOT-3, SOD, MDH-3, 6-PGDH-2 and SDH was confirmed from gametic segregation in haploid endosperm. In addition to observing three new, invariant, zones of isozyme activity, a new polymorphic MDH locus (Mdh-2) and a new allele at Mdh-3 (Mdh-3/93) were found. Thus, at least two loci, with two and three alleles, respectively, code for MDH in this species.
In our preliminary analyses, allele Got-3/50 was discovered in only two trees and Mdh-3/93 was found in only one tree. A marginal population situated in the most arid zone of the natural distribution of A. chilensis (300 mm annual rainfall) was the only population sampled that showed variation at the Mdh-2 locus. In both rainfall transects, average degree of heterozygosity for five loci increased with increasing aridity (.143.238 and .042.275), and in one transect this trend was statistically significant at 5 percent probability.
Key words: Austrocedrus chilensis, allozymes, inheritance, actual heterozygosity, ecological genetics.
Correspondence: Mario Pastorino, Instituto Nacional de tecnología Agropecuaria (I.N.T.A.), CC 277, 8400 San Carlos de Bariloche, Argentina
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