| Induction of apomixis in Aegilops squarrosa
L. U. KUSHNIR and G.M. HALLORAN School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria 3052, Australia The term apomixis embraces all types of asexual reproduction that tend to replace or act as substitutes for the sexual method (STEBBINS 1950). The phenomenon was discovered in the Gramineae, in Poa, by MUNTZINB (1933). Thirty two genera of grasses have been subsequently reported to contain apomictic species (CONNOR 1979) but no occurrence has been reported in the genera Aegilops or Triticum. GUSTAFFSON (1947) maintained that in diploid and tetraploid species growing under unfavourable environmental conditions such as long or short day, low light intensity or temperature, flower formation or seed setting may be restricted or prevented. In the present study evidence is presented for environmental induction of apomictic vegetative reproduction in Aegliops squarrosa. Materials and Methods This study was based on a strain of Aegilops squarrosa var. "meyeri" which was collected in Iran by Kyoto University Scientific Expedition (KUSE 2144) and kindly supplied by N. NAKAI, Laboratory of Genetics, Faculty of Agriculture, Kyoto University, Kyoto. This strain, which has a strong vernalization response, was grown under two treatments with four plants per treatment. In one treatment the seed did not receive vernalization and was sown at the end of summer in pots in a glasshouse maintained at approximately 20C under 16h photoperiod (natural photoperiod extended to 16h using incandescent lights) for two months and then transferred to natural photoperiod (9.4-11.5 h) at the same temperature. In the second treatment imbibed seed was given ten weeks vernalization after which the seedlings were sown in the glasshouse under natural photoperiod (9.4-11.5 h) with the unvernalized plants. For vernalization, imbibed seeds were placed in a cold room at 4C under an 8hour photoperiod provided by low intensity (photoinductive) incandescent light. Results and Discussion The vernalized plants grew normally and produced culms that headed 140-150 days after planting out after vernalization (Fig. 1). The unvernalized plants were much more profusely tillered than the vernalized plants. Their culms exhibited internode elongation but most of them did not head, remaining as "blind shoots". Very few culms (2-3 per plant) headed, producing only small heads, which occurred 210-215 days after sowing. Of the tillers that headed, internode elongation occurred long before the appearance of the head. In both the headed and non-headed culms of the unvernalized plants, axillary buds developed at the culm nodes to give plantlets with initial roots (Fig. 2). This phenomenon occurred in all the plants of unvernalized treatment. |
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