The boeoticum x urartu hybrids, irrespective of the female parents, were completely self-sterile (JOHNSON and DHALIWAL 1976). Similarly, all the monococcum x urartu hybrids (Table 1) without regard to the female parent were self-sterile indicating that T. monococcum like T. boeoticum is reproductively isolated from T. urartu. Hybrids involving T. monococcum and T. boeoticum were completely fertile suggesting that the urartu genes responsible for the boeoticum x urartu hybrid sterility were not introgressed in the parental population of T. monococcum. It suggests further that only a very limited amount of the urartu genome is represented in T. monococcum.

Fertility of the BCI progenies (boeoticum x urartu) x boeoticum and (boeoticum x urartu) x urartu (Table 2) suggests that the introgression would have been possible only from T. urartu to T. boeoticum rather than in the opposite direction. Plants from the BCI progeny (boeoticum x urartu) x urartu were essentially completely male and female sterile while that from (boeoticum x urartu) x boeoticum had very low to very high fertility (Table 2). Presumably due to segregation or further backcrossing of the BCI progeny (boeoticum x urartu) x boeoticum with T. boeoticum only a fraction of the urartu genome was retained. The facts that under natural conditions viable hybrid seeds are possible only with T. boeoticum as the female parent and substitution of the urartu nucleus in the boeoticum cytoplasm gives male sterile plants (DHALIWAL 1976) indicate further that the introgression of T. boeoticum to T. urartu could not have possibly occurred.

With respect to certain plant and spikelet characteristics such as leaf pubescence, seed colour and spike density (Table 3) T. monococcum resembles T. urartu rather than T. boeoticum indicating further that the boeoticum population from which T. monococcum was domesticated involved introgression of T. urartu. However, a close resemblance of T. monococcum to the contemporary cultivated tetraploid wheat T. dicoccum (Table 3) suggests that T. monococcum might have originated as a result of introgression of the tetraploid to T. boeoticum. Alternatively. T. monococcum was domesticated first and T. dicoccum originated as a results of introgression of T. monococcum into wild tetraploid wheat. Available archaeological evidence (HALBAEK 1959, 1966) does not provide answer as to which of the two was domesticated first. Experimental evidence (DHALIWAL, unpublished), however, suggests that the introgression from diploid to tetraploid wheats can occur easily while it is almost impossible in the opposite direction.

At present T. monoococcum is cultivated on a limited scale in Yugoslavia, Asia Minor, Transcaucasia and North Africa. However, in the past it was cultivated over a very large area extending beyond the distribution of wild einkorn. T. monococcum accessions from different sources are remarkably similar in their growth habit and morphological characteristics. They have erect growth habit, pale green colour, dense spike, dimorphic awns, glabrous-leaves, -leaf sheaths and -glumes, and identical seed shape. The wild diploid wheats vary considerably over the area of their distribution. Uniformity of T. monococcum suggests that it was probably domesticated only at one place.
Conclusion: Evidence from morphology and cross-compatibility of diploid wheats and fertility of the F₁ hybrids among them suggests that T. monococcum was presumably domesticated only once from a population of T. boeoticum involving introgression from T. urartu. Experimental evidence suggests that the introgression could have been possible only from T. urartu to T. boeoticum but not in the opposite direction. (Supported by D.F. JONES' postdoctoral fellowship to the author)

(Received Feb. 3, 1977)