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I. Research Notes Triticum zhukovskyii as a source of male sterile cytoplasm and fertility restorer genes R. S. RANA and M. S. SWAMINATHAN Indian Agricultural Research Institute, Division of Genetics, New Delhi-12 India Male sterility conditioned by cytoplasm was first reported in wheat by KIHARA (1951, Cytologia 16: 177) who transferred the chromosome complement of common wheat (2n=42) into the cytoplasm of Aegilops caudata (2n=14) by successive backcrossing. FUKASAWA (1953, Cytologia 18: 167) similarly transferred cytoplasmic male sterility from Aegilops ovata (2n=28) into emmer and durum wheats (2n=28) and later (1958, W.I.S. 7: 21) observed that a variety of the wild emmer, Kotschyanum (2n=28), when used as the pollen parent, restored fertility of the male sterile lines. This source of male sterility was later transferred to some commercial common wheat varieties by workers in Kansas State University, U.S.A. However, the common wheat varieties used thus far as pollinators of these male-sterile types have produced only male-sterile hybrids. Subsequently, a more promising sterility system was developed (WILSON and Ross 1962, W.I.S. 14: 29) by obtaining through backcrossing the chromosomes of the common wheat Bison in the cytoplasm of T. timopheevi (2n=28). The male sterile Bison strain thus developed was pollinated with a hexaploid wheat having T. timopheevi in its ancestry and fertile plants were produced (SCHMIDT, JOHNSON and MAAN 1962, Nebr. Exp. Sta. Qtrly. 9: 1). Thus, T. timopheevi turned out to be the source of cytoplasmic male sterility as well as of the nuclear genes restoring pollen fertility. Recently, two additional sources of this system were indicated by MAAN and LUCKEN (1967, W.I.S. 23-24: 6) in crosses involving T. zhukovskyi and a T. boeoticum-type diploid wheat. During our study of the phylogenetic relationships among Triticum species, we crossed T. zhukovskyi (2n=42) with a common wheat variety N.P.876 reciprocally in March, 1963. The plants raised from the seeds borne on the zhukovskyi parent were invariably male sterile whereas the plants obtained from the reciprocal cross were fertile. These male sterile lines, being maintained here by hand-pollination, gave progeny segregating for varying degrees of male fertility when pollinated by T. zhukovskyi. Two lines selected from this material produced anthers with fertile pollen and a cytological study of microsporogenesis in these plants revealed that they had largely a normal meiosis. The preliminary data on recombination analysis indicated that more than two genes were involved in this system. The present observations show that T. zhukovskyi, like T. timopheevi, possesses "sterile" cytoplasm as well as nuclear factors for fertility restoration. T. zhukovskyi is morphologically very similar to T. timopheevi and was in fact considered as a form of the latter until JAKUBZINER (1959, Proc. First Intern. Wheat Genet. Symp.: 207) raised it to the species level. UPADHYA and SWAMINATHAN (1963, Chromosome14: 589) showed that T. zhukovskyi probably arose through chromosome doubling in the cross T. timopheevi x T. monococcum var. hornemanni. WAGENAAR (1961. Canad. J. Genet. Cytol. 3: 47) showed that T. timopheevi causes male sterility through a desynaptic mechanism and UPADHYA and SWAMI NATHAN (1965, Indian J. Genet. 25: 1) observed a similar desynaptic system in T. zhukovskyi. Our observations indicate that T. zhukovskyi, being hexaploid like the common wheat, can conveniently replace the tetraploid T. timopheevi as a source of both the male sterilityfertility restoration mechanism and the disease resistance normally associated with the latter. (Received February 12, 1968) |