| Spontaneous speltoid and compactoid mutants in male
sterile lines of T. aestivum and T. sphaerococcum carrying
T. timopheevi cytoplasma R. K. MIRI Division of Genetics, Indian Agricultural Research Institute, New Delhi, India In our studies on hybrid wheat with T. timopheevi system of cytoplasmic-genetic male sterility and fertility restoration involving conversion programme of male sterile (A-line) and fertility restorer (R-line) lines in more than hundred spring wheat varieties, we have noticed a few spontaneous mutants for ear characters and likewise, also in T. sphaerococcum in which timopheevi cytoplasm was incorporated. Segregating Selkirk and Pembina stocks carrying T. timopheevi cytoplasm and genes for fertility restoration used in our investigation were kindly supplied by Dr. A. B. CAMPBELL, Canada Department of Agriculture, Winnipeg, Manitoba, Canada. Four speltoid plants found in male sterile selfed BC1 (partially fertile plants from BC1) progenies of C 306, PV 18, Kalyansona and S 310 varieties in a population of 2412 plants were partially fertile, most of the spikelets in a ear produced abnormal anthers which did not shed viable pollen, whereas none was found in a population of more than one million plants from male fertile, selfed BC1 progenies carring timopheevi cytoplasm and fertility restorer genes. The ears of these plants showed elongation of rachillae with varying degrees of laxness with maximum being more than double the ear length of that of the original wheat variety and had strongly keeled, tight glumes. From male sterile selfed BC2 (Partially fertile plants from BC2) progenies of Sherbati Sonora in a population of 3181 plants three partially fertile plants were found, two had lax ears and tight glumes resembling those of T. spelta and one was like T. compactum, while in more than one million plants from male fertile selfed BC2 progenies not a single such plant was found. Seeds from these three plants when grown produced plants with ears resembling with those of T. spelta and T. compactum. Such plants were not found in BC1, BC2 and selfed BC3 male sterile progenies. One speltoid was found in F2 population of 210 plants of T. sphaerococcum male sterile line. This plant was highly male sterile but set few seeds which when grown in the following season produced plants with spelta like ears. All these eight mutants were recovered from a population of more than two and half a million plants. Cytoplasmic effects may cause reduction in plant height and shortening of internodes, as our observations show that dwarf plants arise occasionally in early generation materials during conversion programme of A-line and R-line in wheat varieties. Such cytoplasmic effects have been reported by DUVICK (1965) in corn. Since the frequency of speltoid and compactoid heads in male sterile plant population is considerably lower than that of dwarf plants and since the progeny of these ear types show spelta and compactum type ear characters the possibility of cytoplasmic effects can be ruled out and presumably here mutation at the Q locus is involved. Only after hybridization of these mutants with normal wheat varieties and their genetic analysis, which we have under way now, it will be possible to ascertain their exact nature. SWAMINATHAN (1965) has provided experimental evidence that speltoid and compactoid mutants arise following induced mutations at the Q locus situated at the long arm of chromosome 5A in the sub-species vulgare, compactum and sphaerococcum. He suggested that spontaneous speltoid and compactoid mutants may occur frequently in populations of these three subspecies following unequal crossing over within the locus. MASSON and ANDERSON (1962) have reported spontaneous occurrence of speltoid mutants in populations of Selkirk, Pembina, Thatcher, Redman and Regent, commercially grown wheat varieties in Western Canada. Due to inadequate development of vascular bundles in the anthers of male sterile plants transmission of some substances, DNA and RNA, from tapetal cells to the developing microspores is restricted (JOPPA et al. 1966 and DUVICK 1965). Hence, it is quite likely that the male sterility inducing timopheevi cytoplasm which affects the microgametogenesis adversely in T. aestivum and T. sphaerococcum might have provided the environment which perhaps enhanced the possibility of occurrence of mutation at the Q locus resulting in the alteration of the sequence of developmental processes controlling the spikelet density in ears and consequently, phenotypic variations in ear characters arise up to subspecific level. Literature cited DUVICK, D. N. 1965. Cytoplasmic pollen sterility in corn. Advan. Genet. 13: 1-56. JOPPA, L. R., F. H. MCNEAL and J. R. WELSH 1966. Pollen and anther development in cytoplasmic male sterile wheat. Crop Sci. 6: 296-297. MASSON, A. B. and R. G. ANDERSON 1962. Speltoids in wheat. Seed Scoop 8(6): 4-5. SWAMINATHAN, M. S. 1965. The origin of macro- from micro-mutations and factors governing the direction of micro-mutational changes. Proceed. 3rd Inter. Symp. The Impact of Mendelism on Agriculture Biology and Medicine. Ind. Jour. Genet. Pl. Breed. 26A: 29-41. (Received April 15, 1970) |