Comparative allozymic multilocus analysis of genetic diversity in wild barley from Turkmenistan (former USSR) and Israel: implications on sampling strategies.

Owuor, E.,¹; Kimani, P. M.,²; Mendlinger, S.,³; Chweya, J., ² and Whittaker,L. ^4
  1. Institute of Evolution, University of Haifa, Mt. Carmel, 31905 HAIFA, Israel
  2. Department of Crop Science, University of Nairobi, P. O. Box 29053, Nairobi, Kenya
  3. Institutes for Applied Research, Ben Gurion University of the Negev, 1025 Beer Sheva, Israel
  4. Jacob Blaunstein Institute of desert Research, Dept. Life Sciences, Ben Gurion University of the Negev, Sde Boqer Campus, Beer Sheva, Israel

Introduction
Effective conservation and utilization of wild barley germplasm depends on efficient sampling strategies through the identification of useful diversity and their distribution in space. This is a remedy to the narrowing genetic base of cultivated crops as a result of pureline breeding. This diversity loss causes disease and pest vulnerability among cultivated crops and should be prevented by exploring wild crop progenitors. Unfortunately, most wild crop progenitors are unevenly distributed and their levels of polymorphism remain largely unknown (Nevo et al., 1979). Hordeum spontaneum, the immediate evolutionary progenitor of cultivated barley, Hordeum vulgare, (Zohary, 1969) is widely distributed around the Near East Fertile Crescent (Zohary, 1973) which represents the center of diversity and core distribution of the species. However, the distribution of this species also extends through the Mediterranean shores of Egypt to former Soviet central Asia constituting peripheral populations (Zohary and Hopf, 1988).

Material and methods
The 385 individual plants analyzed represent thirteen randomly sampled populations in Israel and Turkmenistan. The ten allozyme systems used were phosphoglucomutase, phosphoglucoisomerase, esterase, malate dehydrogenase, 6-phosphogluconate dehydrogenase, catalase, glucose-6-phosphate dehydrogenase, general protein, glutamate dehydrogenase and acid phosphatase, yielding a total of seventeen scorable loci. The electrophoretic protocol assayed leaf water soluble structural proteins according to Nevo et al., (1984) using Tris-malate, Tris-citrate and Borate.

Results and Discussions
The mean allelic frequencies did not display significant regional variation in their patterns and distribution save for the rare alleles Mdh-1^d and Gp-1^c which appeared in Turkmenistan. The proportion of polymorphic loci was higher among the Turkmenistani (P95%=0.96) than Israeli (P95%=0.87) populations respectively. Nei's diversity index, He, evaluated between regions and populations showed that Turkmenistan (He=0.45) is more genetically diverse as compared to Israel (He=0.40). But this difference was not statistically significant. Shannon Weaver partitioning of diversity, D, (Lewontin, 1972) for the seventeen loci gave the bulk of genetic diversity as contributed by the within population (0.80) than the between population (0.15) and region (0.05) components. Mdh-1, Gp-1 and Est-1 accounted for the inter-regional differences, though not statistically significant. This partitioning of diversity agrees in principle with Lewontin, (1972) where most of the protein variation was apportioned within group as compa red to the between group. It also indicates that much of the observed genetic diversity in wild barley is resident within populations and translated as individual variation. The over 70% polymorphic loci obtained essentially demonstrates the genetic potential of H. spontaneum for barley improvement programs. The higher genetic diversity and polymorphism in peripheral (Turkmenistani) relative to core (Israeli) populations has also been reported in wild wheat (Jopa et al, 1995, in press).

Any hypothesis attempting to explain the differantial polymorphism between core and peripheral distributions must recognize that as species begin to penetrate outlying zones far from their traditional centers of diversity, intense selection pressure begins to operate on the front-line genotypes making them optimize in elite genotypes. This optimization exploits extensive polymorphism as the major "raw-material" hence improving the colonial capacity of the species. In this case, selection at the periphery generates new genotypic combinations that can extend the species' boundary.

The bulk of genetic diversity found within as compared to between populations implies that efficient germplasm sampling should increase the sample sizes within than between populations in order to tap as much useful variability as possible. This should be done within the acceptable minimum number of populations to maintain an efficient sampling option. Sampling populations from both core and peripheral regions will still help to tap rare alleles which are of adaptive significance. Routine sample enrichment should consider morphological marker loci e.g. colormorphs, by attaching sampling indices for morphological variants within random sampling programs.

References
Jopa, L. R., Nevo E., and Beiles, A. (1995). Chromosome translocation in wild populations of tetraploid emmer wheat in Israel and Turkey (in press).

Lewontin R. C. (1972). Apportionment of human diversity. Evol. Biol. 6: 381-398.

Nevo, E., Beiles, A. and Ben-Shlomo, R. (1984). Evolutionary significance of genetic diversity: Ecological, demographic and Life history correlates. Biomathematics 53: 13-213.

Nevo, E., Zohary D., Brown AHD, and Harber M. (1979). Genetic diversity and environmental associations of wild barley, Hordeum spontaneum, in Israel. Evolution 33(3): 815-833.

Zohary D and Hopf M. (1988). Domestication of plants in the Old world. Clarendon, Oxford.

Zohary D. (1973). Geobotanical foundations to the Middle East, Vols 1 and 2. G. Fischer, Stuttgart and Swets and Zeintlinger, Amsterdam.

Zohary, D., (1969). The progenitors of wheat and barley in relation to domestication and agricultural dispersal in the Old world, pp. 47-66. -in Ucko, P. J., DIMBLEY, G. W. (Eds): Gerald Duckworth and co.