MAIZE TOPMOST AXILLARY SHOOT INTERFERENCE WITH LOWER EAR DEVELOPMENT IN-VITRO

Interference by the topmost axillary shoot of maize (Zea mays L.) with the development of lower axillary shoots is well known. However, investigations with intact plants have not clarified whether this involves exertion of a growth retarding effect per se or is due, primarily, to the advantage that the topmost shoot has in competing for nutrients. These possibilities have now been examined by means of in vitro cultures. Topmost, second, and third axillary shoots of maize were excised between the stages of tassel emergence and silking and cultured separately for 11 to 15 d. In such cultures, relative elongation rates of the second and third ears were considerably faster than those of ears in corresponding axillary shoots on intact control plants. In joint cultures of topmost and second axillary shoots taken from the same plants, the topmost shoot grew similarly to shoots cultured separately. However, the elongation of the second shoot (husks, ear, and silk) was conspicuously less than that of equivalent shoots cultured separately. These results suggest exertion of a growth restricting effect of the topmost axillary shoot on lower shoots, that is mediated by the release of a growth inhibitor.