| The expressions of developmental and morphological characters of the (Ae.
sharonensis x T. monococcum) amphidiploid were generally within
the ranges of those in the cereal and "grassy" forms of T. turgidum dicoccoides.
It is presumed that these two forms of dicoccoides represents a range
from primitive ("grassy") to more advanced (cereal) genotypes and are some
indication of genetic differentiation that has occurred within dicoccoides
throughout its evolution. In accord with this postulation the "grassy" (primitive)
form was similar in tiller number per plant and kernel weight to the (Ae.
sharonensis x T. monococcum) amphidiploid. The cereal (advanced)
form of dicoccoides had a much lower tiller number per plant than
the amphidiploid and the "grassy" form, which accords with reports (BAMAKHRAMAH
1974, HALLORAN & PENNELL 198la) on the reduction in tiller number from primitive
to advanced forms in tetraploid wheat. Another possible source of genetic
variation in T. turgidum dicoccoides is repeated hybridization between
T. monococcum and Ae. sharonensis forms with intraspecific
variation in morphological and developmental characters. These observations on the (Ae. sharonensis x T. monococcum) amphidiploid further support Ae. sharonensis candidature as the donor of the B genome of wheat on the grounds of compatibilities in morphological and developmental characters of the amphidiploid with the range found in T. turgidum dicoccoides. The amphidiploid possessed a comparable fertility level with T. monococcum and a much larger kernel weight. The greatly increased kernel weight indicates that the first tetraploids of wheat most likely possessed superior competitive ability over T. monococcum during seedling growth (HALLORAN & PENNELL 1981b) and, hence, in population establishment. This may have been significant in the eventual preeminence of tetraploid over diploid wheat. Literature Cited AITKEN, Y. 1976. Non-destructive method for estimation of tassel initiation in maize (Zea mays L.). J. Aust. Inst. Agric. Sci. 42 : 65-66. BAMAKHRAMAH, H.S. 1979. Comparative growth studies of crop species with special reference to harvest index. M. Agr. Sci. Thesis, University of Melbourne. HALLORAN, G.M. 1976. Genetic analysis of hexaploid wheat, Triticum aestivum, using intervarietal chromosome substitution lines - protein content and grain weight. Euphytica. 25: 65-71. HALLORAN, G.M. & A.L. PENNELL. 1981a. Seedling growth in the different ploidy levels of Triticum. Ann. Bot. (In Press). HALLORAN, G.M. & A.L. PENNELL. 1981b. Grain size and seedling growth in the different ploidy levels of wheat. Ann. Bot. (In press). KUSHNIR, U. & G.M. HALLORAN. 1981. Evidence for Aegilops sharoensis Eig. as the donor of the B genome of wheat. Genetics (In Press). PARODA, C.M. 1977. Studies on the B-genome in polyploid wheat by nucleic acid hybridization. Diss. Abstr. Internat. B 37(12) 5969B. SEARS, E.R. 1941. Amphidiploids in the seven-chromosome Triticinae Mo. Agric. Exp. Stn. Res. Bul. 336: 46 pp. SHEBENSKI, L.H. 1958. Speculation on the impact of the D genome. Procs. 1st Int. Wheat Genet. Symp. Winnipeg (Aug. 11-15, 1958) 237-241. |
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