An assessment of heterozygosity and fitness in Chir pine (Pinus roxburghii Sarg.) using isozymes

A correlation between heterozygosity of genotypes and survival (fitness) was studied in eight natural populations of Pinus roxburghii through isozyme analysis using horizontal starch gel electrophoresis. Under each population, 20 mother trees of different ages (30 to more than 100 years) were selected which were at least 50 m apart. From each tree, eight seeds were assayed for eleven enzyme systems viz., Aconitase, Aspertate aminotransferase, Glutamate dehydrogenase, Isocitrate dehydrogenase, Leucine-amino peptidase, Malate dehydrogenase, Menadione reductase, Phosphoglucose isomerase, Phosphoglucomutase, 6-Phosphogluconate dehydrogenase and Shikimic acid dehdrogenase which were found to be encoded by 18 polymorphic loci. Genetic constitution of the mother trees was determined by analysing endosperms and embryos separately. The number of alleles in the progeny (embryos) and the mother trees varied from 38 to 42 and 34 to 37, respectively, in all the populations. Distribution of degree of heterozygosity and fixation index for the progeny and the mother trees were calculated. The mother trees showed a substantial shift towards higher degree of heterozygosity as compared to the progeny. Fixation index values were significantly higher and negative for the mother trees as compared to the progeny, which revealed that heterozygosity was positively correlated with survival in P. roxburghii.