Camille Ulrich Dzokouo Dzoyem

Conventional breeding involves considerable genetic recombination. To maximize breeding efforts, it is necessary to increase seed yield. This study proposes to improve seed yield by using tetraploid bananas as part of a genetic improvement programme for cooking varieties. To this end, the female fertility (seeding rate and embryo sac maturity) of tetraploid banana plants was characterised. The pollen potential of tetraploids was then assessed at anthesis and at the end of meiosis, as well as during crosses with seminiferous diploids, leading to a phenotypic characterisation of the value of an offspring. This study highlighted the low seed production rate of tetraploid genitors. At best, 7% of seeds are produced per fruit, but 57% of the ovules per fruit have mature embryo sacs. The use of tetraploids as male parents, free from any source of sterility associated with the domestication process, did not generally improve the seed rate, except in the case of FHIA 21 (2930 seeds). Its pollen potential was used in a cross with Banksii 0623 (♀). This resulted in progeny with interesting vigour and phenotypic characteristics. This latter combination has the potential to transfer its “cooking” genetic structure.

The objective of this work was to investigate the causes of sterility in a new set of triploid banana (Musa spp.) cultivars and to assess the chances of obtaining some progenies by manual cross-pollination. The developmental stages of female gametophyte were histologically recorded in ovules of four distinct triploid banana cultivars. Samples were taken on the day of flower opening and pollination and three days later. Morphologically mature embryo sacs were very rare in the two clones of the 'Cavendish' subgroup and in 'Prata Anã'. In 'Mysore', it occurred at a variable and low frequency. In 'Terrinha', it was extremely common. In the last two cases, the embryo sac maturation process was clearly continuing between the sampling days of flower opening and three days later. No pollen tube was positively identified in pollinated flowers within the integuments of any ovule of the older explants. Different proportions of mature embryo sacs are observed among the studied triploid genotypes of banana. The presence of mature embryo sacs is not an indication of functional capacity. Other causes of infertility in cultivated bananas can be due to some event immediately before or after fertilization, for instance, pollination tube growth failure or seed abortion.

The objective of this work was to evaluate the effect of the suppression of female flowers on the pollen fertility of male flowers of banana plants. Two modes of female flower suppression, one partial and one complete, were applied shortly after flowering to diploid, triploid, and tetraploid banana genotypes. The effect of flower suppression on the number of male flowers and the length of their anthers was evaluated, as well as pollen viability and the size and number of pollen grains per anther. Pollination tests were performed to evaluate the number of seed obtained from the progeny of some genotypes. The total suppression of female flowers significantly increases pollen fertility, estimated by an increase in the number of pollen grains per anther (up to 80% per anther). Total female flower suppression also improves significantly seed production in the crosses (from 35 to 160% per pollinated bunch), which suggests a positive influence of the sap flowing through the bunch on the efficiency of banana pollen.