An examination was made of germination events of non-dormant wheat grain, enclosed in the ear, and wet under repeatable conditions in a rain simulator. This formed one part of a study in which several aspects of phenotypic variability associated with germinability of wheat grain were examined. Following imbibition, the germination sequence was sprouting, endosperm degradation, and �-amylase response, which was relatively late in occurrence. Apparently, other germinative enzymes contributed substantially to first endosperm degradation. Selection criteria against sprouting damage were discussed with respect to these sample findings. Also, a sprouting damage score was found to be potentially useful for rapid selection amongst large numbers of populations.
Grain development of embryo dormancy, germinative α-amylase, pigmentation and flavanols was examined in the wheats Timgalen and Gamut (white-grained, non-dormant), and Pembina and Sonora (red-grained with different levels of dormancy). It was found that each trait had distinctive patterns of development. The net result at harvest ripeness depended on the synchronizations amongst the traits. Dormancy, as judged by embryo response (i.e. embryo dormancy), was restricted to the red wheats. Three ways of expressing it were noted: (1) in terms of development patterns, (2) as levels at harvest ripeness or at harvest, and (3) by the length of the period of embryo dormancy after harvest ripeness. Two hypotheses linking embryo dormancy and grain redness appeared plausible from the results. One was that the polyphenol oxidase complex, which polymerizes flavanols to the putative pigment phlobaphene, contributes towards embryo dormancy, probably through enhancement of hypo-oxia. The other was that the pigment itself and its tanning complexes cause the hypo-oxia. Flavanols did not appear to be in vivo germination inhibitors. Dormancy, as judged by α-amylase response (i.e. amylase dormancy), was not always present together with embryo dormancy. A long period of amylase dormancy was found in the more embryo-dormant red wheat, but not in the other. Conversely, a short period of amylase dormancy was found in one white wheat, but it was not embryo-dormant. Possible relationships between these physiological traits and the classical genes for red grain-coat were discussed. Implications concerning selection against sprouting damage were considered.
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*Part II, Aust. J. Agric. Res 30: 1-17 (1979).
Examination of grain development in two white-grained (non-dormant) and two red-grained (varying dormancy) wheat genotypes has clarified concepts of maturity with respect to grain dehydration, harvest ripeness, embryo maturity, base α-amylase activity and dry weight growth. Each maturity trait had a different pattern of development. The net level of grain maturity at harvest ripeness depended on the relative progress of the maturation traits at the time at which harvest ripeness was defined. Harvest ripeness is defined as the first attainment of 12½% moisture during primary dehydration of the grain, this being closely related to fitness for harvest. The effects of adopting other definitions of harvest ripeness (at 17½% and 20% grain moisture) are discussed. Significant differences amongst genotypes in development patterns, temporal placement, and harvest ripeness level were found in each maturity trait, and the differences were not parallel across traits. Differences in maturation did not coincide with differences in putative dormancy or grain colour. Results indicated that grain maturation was a multi-faceted process, with flexible synchronizations amongst maturation traits at any point in time, such as at harvest ripeness. Germination tests or a-amylase assays on progeny grain samples, at some time after harvest ripeness, measure differences in maturity as well as putative differences in dormancy. Interpretation only in terms of dormancy could be misleading. Adjustment for immaturity is discussed.
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*Part I, Aust. J. Agric. Res., 28: 583 (1977).
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