| Imbibed seed was vernalized in a cold room at 4C under 8 hour photoperiod
provided by low intensity (photo-inductive) incandescent light. Following
this treatment eight vernalized and eight non-vernalized seedlings of each
line were planted in two 18 cm diameter pots (four seedlings per pot) containing
a potting mix (1 part washed sand: 1 part Perlite: 1 part Derrimut red brown
loam by volume). The non-vernalized lines were grown under two photoperiod
regimes-short day of 12 hours and long day of 24 hours; the vernalized material
was grown under long photoperiod only. All plants grew under temperatures of 20C (day) and 15C (dark). The number of days from sowing to floral initiation was determined by the non-destructive method of AITKEN (1976).Observations were made of final leaf number, days to anthesis and spikelet number on the main shoot of each plant. Plant height, tiller number, grain number per spikelet, grain number per head, seed fertility (per cent) and kernel weight were measured for the main shoot of the unvernalized plants grown under the short day regime. Results and Discussion The timopheevi-like mutant exhibited similar developmental responses (days to floral initiation, final leaf number and days to anthesis) under both long and short photoperiod as the three lines of T. timopheevi. While its photoperiod response was much stronger than the T. turgidum dicoccoides 'parent' its vernalization response was much lower than it and very similar to the T. timopheevi lines. Since the timopheevi-like somatic mutant has been found to be a product of chromosome rearrangement (KUSHNIR & HALLORAN, a1983a, b),the changed photoperiod sensitivity and vernalization response of the mutant appear to be a consequence of this rearrangement and is a possible explanation for similarity of its developmental pattern with that of the T. timopheevi lines. WAGENAAR (1966) noted similarly that all the introductions of T. timopheevi he obtained from USSR were of spring habit. It is feasible that spring habit of T. timopheevi could have generally arisen from T. turgidum dicoccoides by way of macromutation. Such an occurrence could have provided T. timopheevi with better adaptation to different habitats north of the area of natural distribution of T. turgidum dicoccoides in the southern states of the Soviet Union. This change in ecological range could have caused it to become separated from the parental species. Alternatively, or in conjunction with changes in encological adaptation, the non-shattering character of such a timopheevi-like mutant could have attracted man's attention as being better adapted for domestication and cultivation than shattering tetraploid forms, leading to its propagation and wider geographical distribution. |
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