Abstract:
The nature of allozyme differentiation among Aleppo pine (Pinus halepensis Mill.) circum-Mediterranean populations gave rise to the division of the species into two major subdivisions and several races. In spite of the relatively low values of several genetic parameters in Pinus halepensis, compared with the values of the same parameters in other pine species, there is enough genetic variation to enable selection and adaptation to stressful environments, within and outside the natural range of distribution of the species. Aleppo pine F 1-offspring, grown from seeds collected in natural native Israeli and overseas populations, were planted in 1985 in two provenance trials. One of the trials was established under drought-prone environmental conditions at the northern edge of the Israeli Negev Desert (the Yatir Forest), to mimic the ecological changes resulting from global climate change. We tested whether these 13-year-old F1-offspring populations exhibited genetic diversity and structure similar to those of their parental origin populations. We also measured several eco-physiological properties, to elucidate eventual differences between provenances in their response to drought. After 13 years, in 1997, the survival rate of the 23 provenances averaged 75 ± 13 %, and ranged between 46 and 92 %. The survival rate in 2000 declined to an average of 38 ± 21 %, with a range from 0.0 to 92 %; this was because of two successive winter droughts, with only 144 and 155 mm rainfall in the winters of 1998/99 and 1999/2000, respectively. This was the most severe such event ever recorded in the region. The genetic diversity of the provenances was determined in 1997/1998 by means of isoenzyme analysis by starch gel electrophoresis, and by means of genome DNA analysis by RAPD-based PCR. The percentage of polymorphic loci increased from an average of 40 % in the natural populations to 46 % in the F1-offspring populations at Yatir. The average number of alleles per locus (A/L) rose from 1.3 in the parental populations to 1.5 in the offspring populations and, consequently, the observed heterozygosity rose from 0.049 and 0.115 respectively in the parental populations to 0.160 and 0.144, respectively, in the Yatir populations. The average observed heterozygosity rose from 0.118 to 0.167. The largest changes in diversity, heterozygosity and fixation index occurred in the population that had originated in the highest and wettest environment, whereas only relatively minor changes occurred in those from relatively drier environments. Analysis by means of RAPD-based PCR showed that gene diversity (h) rose from 0.264 and 0.303, respectively, in the parental natural populations to 0.431 and 0.406 in Yatir. The calculated linear regression between allozyme heterozygosity and gene diversity (RAPD) resulted in r = 0.690, P < 0.001. Planting in dryland areas, outside the natural area of distribution of a species, can be looked upon as the creation of man-made peripheral populations as defined by SAFRIEL et al. (1994). Such populations will have higher genetic diversity than natural populations - conferred by selection pressure that eliminates the homozygous and favors the heterozygous genomes - and consequently have more resistance to extreme conditions. Therefore, plantations of such populations should be established and treated as a biogenetic resource, available for rehabilitation and restoration of damaged natural or planted Aleppo pine ecosystems. © Arbora Publishers.
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