Ecogeography and Demography of Cicer judaicum Boiss., a Wild Annual Relative of Domesticated Chickpea

Chickpea (Cicer arietinum L.) is a major pulse crop in the Indian subcontinent and other world regions and is characterized by narrow adaptation relative to other cool season food legumes. Comparative ecophysiology employing closely related wild species is a powerful tool to broaden the understanding of the genetic and physiological basis of crop adaptation. However, meager data are available on the ecological preferences of annual wild Cicer species. Moreover, the geographic range, its size, shape, and boundaries as well as its internal structure have never been studied for any of the wild Cicer taxa, thereby limiting our understanding of Cicer biology. Accordingly, this work focused on Israeli C. judaicum Boiss. a wild annual relative of chickpea. We defined the range of the species across the Mediterranean zone of Israel, characterized the ecogeographical profile of its habitats and studied two populated sites at the macroand microsite levels in terms of plant density, frequency, and niche physical characteristics. Throughout the survey area the species is mostly confined to stony and rocky niches where competition with more aggressive annuals is small. This habitat preference dictates a patchy distribution pattern at all levels, from local niche to the region and beyond. CHICKPEA is a grain legume associated with the initiation of agriculture in the Neolithic Near East (Lev-Yadun et al., 2000; Zohary and Hopf, 2000). Annual world production of chickpea amounts to approximately 8 3 10 Mg, a lion’s share of it (94%) in developing countries, mainly in the Indian subcontinent (FAO, 2006). Large population sectors in India and its neighboring countries, many of them vegetarian, depend on chickpea as a main dietary protein source, while in developed countries it is considered a health food (e.g., Abbo et al., 2005). In a recent review on the evolution of domesticated chickpea (Abbo et al., 2003), the authors suggested that the restricted distribution of C. reticulatum Ladiz. (the immediate wild progenitor) poses severe limitations on the adaptation of the crop. These authors hypothesized that the narrow adaptation of C. reticulatum (as deduced from its restricted natural distribution) represents (or stems from) limited genetic variation in key adaptive loci (e.g., temperature and day-length response genes and edaphic requirements). Further, this narrow genetic variation could partly account for the adaptive limitations of domesticated chickpea compared with other cool season grain legumes (e.g., Abbo et al., 2003; Siddique et al., 1999; Turner et al., 2001). Indeed, in their review of pulse crops adaptation in the Canadian and U.S. northern Great Plains, Miller et al. (2002) noted that chickpea has an “unusual response to growth season rainfall” and that pea and lentils had broader adaptation compared with chickpea. Miller et al. (2002) also stressed that “comparative adaptation among pulse crops remains poorly understood.” Regardless of the evolutionary and agronomic reasons for the failure of chickpea to occupy a major niche among the autumn sown crops of temperate latitudes, understanding the genetic and physiological basis of adaptation is fundamental for future improvement of chickpea and other crop plants (e.g., Evans, 1993). The closely related wild relatives of crop plants provide excellent material to study the potential adaptation spectrum of the respective crops (Evans, 1993). Ecophysiology and comparative physiology are key components in such an approach (therein), provided there is a wide range of germplasm lines representing a sufficiently wide ecological spectrum. In the case of Cicer, however, the number of independent wild annual accessions found in genebanks is relatively small (Berger et al., 2003). The data available from the annual Cicer world collection indicate that they provide incomplete coverage of the geographical distribution of the taxa and thus probably also of their genetic diversity (Berger et al., 2003). As part of our ongoing project aimed at broadening the understanding of the genetic and physiological basis of chickpea adaptation, we focused in this study on C. judaicum, an annual wild taxon and a member of the tertiary genepool of the cultigen (Ladizinsky and Adler, 1976). This species is cross-compatible with C. bijugum Rech. f., which grows in higher latitudes (Ladizinsky and Adler, 1976), making both taxa suitable parents for segregating populations to study the genetic basis of adaptation (Abbo et al., 2003; Berger et al., 2003). The specific aims of this work were as follows: first, to define the geographic range of C. judaicum across the Mediterranean zones of Israel and characterize this range by its size, shape, boundaries and internal structure; second, to identify ecogeographic patterns in the distribution of C. judaicum by using Geographic Information Systems (GIS) and multivariate analyses; and third, to characterize the local spatial pattern of C. judaicum plants, their density, frequency, and preferred microhabitats by focusing on two selected populations. MATERIALS AND METHODS