| Subculture of Rye Callus Rye callus has been repeatedly subcultured on the basal medium. This callus has a morphology different from that of wheat or the hybrid. It is white, often with a greenish core, and is distinctive in often producing an extensive, loose surface layer which is fluted or layered. There has been no tendency for organ differentiation on the basal medium. Subculture of Wheat-Rye Callus The hybrid callus has been repeatedly subcultured on the basal medium, where it grows as a white to yellowish- or cream-colored callus with a smooth to slightly rough surface. This callus was subcultured onto the same 27 different media described in the subculturing of wheat callus. The best growth was clearly shown on the Linsmaier and Skoog medium supplemented with casamino acids only. On this medium 2% sucrose appeared to be superior. The next best medium for callus growth was the same medium supplemented with both casamino acids and yeast extract. In this case 4% sucrose was superior. The other media gave fair to poor results, with the least growth occurring on the modified White's medium. On this medium the callus remained whitish where casamino acids only were added to the medium; however, when yeast extract was added in combination with casamino acids or alone, the callus became brown- or tan-colored and little or no growth was observed. Generally, except as noted above, sucrose concentration had little effect on callus growth. The hybrid callus resembled the wheat callus only to a limited degree in its growth response on the 27 different media. Best growth was on the Linsmaier and Skoog standard medium rather than the same medium containing a modified amount of basal salts. Although poorest growth was on the modified White's medium; as was the case with wheat callus, the hybrid callus was even poorer on the modified White medium containing yeast extract, both in combination with casamino acids or alone. This is opposite from the response of wheat callus to the addition of yeast extract to this medium. Comparative Growth Responses Since wheat callus was reported previously to grow on the B-5 medium (GAMBORG and EVELEIGH, 1968; GAMBORG, 1970; and GAMBORG and SHYLUK, 1970) and by SCHENK and HILDEBRANDT (1972) on their medium, a series of cultures was established to compare the growth of the wheat, rye, and wheat-rye callus on these two media to their growth rate on Linsmaier and Skoog's medium. Ten subcultures of each kind of callus were established on 20 ml of each of the three kinds of media. All three media contained 2% sucrose, 1 g/l of casamino acids, and 4 mg/l of 2,4-D. Explant sizes were 25 mg of rye callus, 25 mg of the wheat, and 20 mg of the hybrid. The ninety tubes were divided into two groups of 45 each. One group was kept in continuous dark while the other group was kept in the usual alternating light-dark cycle. After 40 days at 25C the cultures were harvested and fresh weights were obtained. The results of the experiment may be summarized as follows. All three kinds of callus grew to some extent on the three kinds of media. The wheat callus grew the most and the rye callus the least. For each kind of callus, the growth response was similar for the three kinds of media, and little difference was noted between growth rate of callus grown in a light-dark cycle and that grown in continuous dark. The growth response was quite variable, with the standard deviations exceeding the mean increase in fresh weight in most cases. This variability as well as the generally slow rate of growth was probably a result of the small size of the explants, since it has been observed that larger explants (100 mg or larger) commence growth more rapidly and fail to grow less often than the small explants used in this experiment. |
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