Geographical distribution of B chromosomes in Aegilops mutica Boiss., a wild relative of wheat

The morphology and frequency of B chromosomes (Bs) in Aegilops mutica were examined using materials collected From 16 natural populations in Turkey an d Iran covering almost the entire distribution area of the species. Among 5 78 plants examined. 173 (29.9%) from 14 populations were found to have one to fives Bs. Bs were distributed over the entire geographical area examined . All of the Bs detected were similar in morphology, suggesting their monop hyletic origin. The plants with 2Bs were dominant among the B-carrying plan ts in most populations. Judging from these results, it was suggested that B s originated. at the latest, at an early stage after the specification of A e, mutica, spread by mass migration of outbreeding Ae. mutica, and have bee n maintained in populations bq; directed non-disjunction during first polle n grain mitosis. The Frequency of B-carrying plants and the mean number of Bs per plant were significantly heterogeneous among populations. No correla tion was detected, however. between B frequency and the environmental Facto rs of collection sires. Furthermore, the homogeneous proportion of plants w ith 1B. 2Bs and more than 2Bs among populations suggested no difference in the: directed non-disjunction rate among Bs. Based on these results, it was suggested that the significant difference in B Frequency was due to the di fference nor in directed non-disjunction rate but in nonpaired B loss rate during meiosis.