Genetic Variation and Its Geographical Distribution in Aegilops caudata L.: Morphology, Hybrid Sterility and Gametocidal Genes

Abstract Aegilops caudata L. is a diploid wild relative of wheat with the main distribution in the northeastern Mediterranean basin from Greece to northern Iraq. Two varieties are taxonomically described in this species based on spike morphology. In the present work, to elucidate the geographical differentiation pattern of the species, the geographical distribution of the two varieties was reviewed, 35 accessions derived from the entire distribution area were crossed with the four Tester lines, two varieties derived from their sympatric stands on the Aegean Islands were crossed with each other, and their F1, F2 and/or BC1F1 populations were examined. It became clear that the present distribution area of Ae. caudata can be divided into the western and eastern regions with the border in the mountains lying between West Anatolia and Central Anatolia: the western and eastern accessions are isolated not only geographically but also reproductively by hybrid sterility caused by gametocidal-like genes, and the morphology of var. typica is controlled by two different genotypes in the western and eastern regions. It was suggested that Ae. caudata occurred in the two isolated refuges during the maximum glacial period, the Aegean region and the western Levant or some sheltered habitats in the East Taurus/ Zagros mountains arc, and that the latter population now occurs in the eastern region while the former now occupies the western region of the distribution.

The genus Aegilops L. consists of about 25 species, and the morphological variation and the geographical distribution of the each species and the infraspecific taxa were described in detail in 1920s (Zhukovsky 1928; Eig 1929). And two new taxonomic systems were recently published (Hammer 1980; van Slageren 1994). However, the treatment of infraspecific taxa differed so much from author to author. Genetic reassessment of infraspecific taxa is essential to biosystematic approach to the better understanding of the diversity and speciation process of the each species, because some infraspecific taxa are phylogenetically significant but others are not. Aegilops caudata L. (syn. Ae. markgrafii (Greuter) Hammer) is a diploid wild relative of wheat. Two varieties are taxonomically described in this species based on spike morphology, var. typica with a well-developed awn on the empty glumes of only apical spikelets and var. polyathera Boiss. with an awn on the empty glumes of both the apical and lateral spikelets.

In the present work, to elucidate the geographical differentiation pattern of Ae. caudata, the geographical distribution of the two varieties was reviewed, 35 accessions derived from the entire distribution area were crossed with the four Tester lines, two varieties derived from their sympatric stands on the Aegean Islands were crossed with each other, and their F1, F2 and/or BC1F1 populations were examined.

Geographical Distribution of the Two Varieties

Ae. caudata distributes from the southern Balkan Peninsula to Afghanistan with its main distribution in the northeastern Mediterranean basin from Greece to northern Iraq (Eig 1929; Bor 1968, 1970; Tutin and Humphries 1980). Based on the geographical distribution of the two varieties described in the literature (de Halácsy 1904; Hayek 1927; Eig 1929; Rechinger 1943; Bor 1968, 1970; Tanaka 1983a) and the collection lists published by Kyoto University (Tanaka 1983b; Sakamoto 1986), the main distribution area of the species can be divided into the three geographical regions according to the geographical division by Davis (1965): (1) The Greek mainland, the Aegean Islands and West Anatolia, where the two varieties occur with the predominant occurrence of var. typica, and their sympatric stands are common;

(2) South Anatolia, East Anatolia, Iraq and Syria, where the two varieties occur but their sympatric stands are rare; and (3) Central Anatolia, where var. polyathera occurs exclusively.

 
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