Cytological studies in the Musae; meiosis in some diploid clones.

HE banana breeding program currently being carried out in Jamaica T is largely based on the progeny of the triploid (zn=33) Gros Michel crossed with a number of naturally occurring diploids. The bulk of such progeny have been found to be tetraploid (LARTER 1935 and unpublished; CHEESMAN and DODDS 1942), which suggests that Gros Michel has a tendency to throw a majority of triploids among its viable gametes. The mechanism involved is presumably the formation of restitution nuclei or the suppression of one or the other of the two meiotic divisions. A cytological survey of relevant material has been carried out partly with the hope of finding evidence concerning this hypothesis and partly to lay a cytological foundation for more extensive cytogenetical and cytotaxonomical studies than have hitherto been carried out. The first paper of this series (WILSON 1946) dealt with several triploids representing the three groups, Cavendish-Robusta, Gros Michel, and the plantains. The present paper deals with several species of diploids with special reference to the Musa acuminata group from which virtually all of the successful crosses have been made. The third paper will be largely concerned with the more extensive seedling families from the general cross Gros Michel XM. acuminata. With reference to Gros Michel, the cytological findings were in agreement with the “restitution nuclei” hypothesis in so much as definite evidence of a tendency to suppression of the first division of meiosis was found. This of course presupposes normality on the part of the diploid male parents-an assumption borne out by the data to be presented below.