Growth and development of ovules of banana, plantain and enset (Musaceae)

Abstract Sterility has profound effects on the development of reproductive tissues in members of the Musaceae and limits genetic improvement required to deal with new diseases. Ovules of seeded diploid Musa acuminata (AA) and edible triploids (AAA) from the same cytogenetic group, plus edible triploids containing genomes of the M. balbisiana cytogenetic group (AAB, ABB) and the related genus Ensete sp. were studied to determine the effects of sterility on the growth and development of the ovule and its tissues. Specimens were collected from subtropical and Mediterranean environments in Australia. At anthesis, the ovules of triploid plants were 36% larger than the ovules of diploid plants. The diploid ovules ceased growth shortly after the inflorescence emerged from the pseudostem. In contrast, the triploid ovules continued to grow 7–10 days past anthesis, increasing in size by 70%. All ovules of diploid M. acuminata ssp. had an embryo sac at anthesis, against 97% for triploids. At anthesis the embryo sacs in diploid ovules occupied 2.7% of the nucellus compared with 1.5% in triploid ovules. The embryo sacs did not grow between bunch emergence and anthesis, once formed they maintained the same size. Many embryo sacs were not positioned correctly, flush with the nucellar cap. The diploid M. acuminata ssp. had 75% of embryo sacs correctly positioned against 10% in the edible triploids. The proportion of balbisiana genome (B) did not affect ovule or nucellus size or shape, or cell number across the nucellus. It increased the embryo sac presence 96–100% of ovules. The sterile edible triploid bananas have embryo sacs at anthesis but many are incorrectly positioned, which may contribute to their sterility. The balbisiana genome in the edible triploids was associated with a 2.4-fold increase in the number of correctly positioned embryo sacs and this may contribute to the increased fertility associated with the B genome.