Shoot tip culture is used extensively to propagate clones of ornamental plants and a few crop plants. Its use in grass crops appears untried, but because it could be a source of more stable lines than through callus cultures it deserves some attention. The procedure utilizes the fact that stems possess axillary buds which, following release from apical dominance, can produce new shoots. These can then be used to generate secondary axillary buds. A scheme for such procedure is illustrated on the following page.
Some preliminary tests to determine how corn would respond in such a culture protocol generated the following observations:
Step I: Young 10-20 day shoot tips with all leaves removed possessing up to 10 axillary buds plus a terminal apex can be successfully cultured on appropriate sterile media. Axillary buds develop profusely and can be subcultured (Step III). Variations in this response appear to be stock-related and decidedly media-related.
Step III: Successful culture of the primary axillary buds is now routine though as yet second-order axillary buds have not been successfully subcultured.
Step IV: Roots do not initiate on the media used in Step I. Therefore a transfer is required. Apparently, the temperature and day length conditions are important for this step.
Step V: To date 6 plants derived from axillary buds have been successfully potted. We are following their development.
Despite the limited success of this procedure, a number of problems remain. For example, axillary buds in corn are probably not easily diverted from their normal developmental pattern as is the case in other plants. Axillary buds, at least by the 20-30 day stage, are probably differentiated as tiller, ear-shoot or some intermediate condition. The reversion of these buds to freely leaf-initiating meristems may prove difficult.
K. Raman
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