Spatial and Temporal Genetic Structure of Wild Emmer Wheat in Jordan. Ii. High-molecular-weight Glutenins and Allozymes

A study was designed to sample and characterize 12 populations of wild emmer wheat in Jordan at the high-molecular-weight (HMW) glutenin and allozyme levels. Data were collected and individual plants were sampled from 207 permanent sampling points in three central, three peripheral, and six marginal populations during all or part of a five-year study period. Patterns of variation, based on four HMWglutenin and 36 allozyme loci, were used in characterizing these populations. Polymorphisms, based on HMW-glutenins and allozymes, decreased with increasing aridity of the collection site. A large portion of the HMW-glutenin(61.1%) and allozyme (62.7%) variant alleles were localized. Gene differentiation estimates, based on HMW-glutenins and allozymes among (60.8 and 65.8%, respectively) and within (39.2 and 34.2%, respectively) populations, were high and comparatively similar; however less variation was partitioned among the Jordanian populations when compared to populations in the more mesic parts of the Fertile Crescent. Environmental heterogeneity may have been involved in generating significant spatial structuring in these populations at the HMW-glutenin and allozyme levels. A gradual increase in allozymic monomorphism with aridity suggests that polymorphism is more likely to be found in heterogeneous environments. Changes in population size and total loss of small populations are warning signs that these populations may be vulnerable. Results of the present study are expected to complement the existing body of knowledge on the species and enhance the understanding of its genetic differentiation and evolution across large parts of the Fertile Crescent. The preservation of the endangered, and yet valuable, genetic diversity present in Jordanian wild emmer wheat populations, as an integral part of a holistic regional approach to biodiversity conservation, is urgent. Present address: Plant Genetic Resources Program, International Center for Biosaline Agriculture, ICBA P.O. Box 14660, Dubai, UAE. E-mail: [email protected] INTRODUCTION Wild plant populations adapt, at the morphological (Allard et al., 1968), developmental (Jaradat and Humeid, 1990), allozyme (Nevo, 1987; Nevo et al., 1988a,b, 1991; Nevo and Beiles, 1989), and seed storage protein (Levy and Feldman, 1988; 1989; Nevo, 1983; Felsenburg et al., 1991) levels, to habitat variation to meet the local macroand microenvironmental conditions. This adaptation potential in wild emmer wheat explains its distribution over a large ecological amplitude in the Fertile Crescent. A few studies (Felsenburg et al., 1991; Nevo et al., 1991) have addressed the long-term fluctuation in the range and pattern of genetic variation, both within and among populations of wild emmer wheat, as affected by yearly climatic changes. Information from such longterm studies is necessary for devising better strategies for the in situ conservation and ex situ sampling of the