Female Reproductive Potential and 3x by 2x Breeding Approach for Hybrid Seeds Development in Sukali Ndizi Genotype (Musa genome AAB)

Abstract

Sukali Ndizi is one of the most popular local desert banana cultivars in Uganda. The crop is affected by a number of diseases and pests. Genetic improvement of the crop by hybridization may be hindered by very low seed set and poor seed germination. The main characteristics for assessing the female reproductive potential (seed set, seed quality and embryo germination of hybrid seeds) and 3x by 2x breeding approach were assessed in crosses of eleven different male diploid parents either wild or improved diploids with Sukali Ndizi landrace as the female parent for a period of 5 consecutive years planted in pollination blocks at National Agricultural Research Laboratories Kawanda (NARL). The month of pollination did not show any pattern throughout the pollination period but the crosses showed considerable variability in seed set, seed quality, and seed germination for different male diploids used. The water gravity test which differentiated the extracted seeds as sunken/viable and floating/nonviable seeds showed that a substantial amount of seed was floating and the sunken externally characterized by black hard integuments was only 39% with a range = 24%–60% which contained embryos, of which 22% (range = 0–37%) germinated. The increase in non-viable seed suggested that ovule abortion in Sukali Ndizi which mainly involved embryo and endosperm abortions was the cause of limited seed germination and the paternity of the zygotes was a major factor underlying abortions. Flow cytometric analysis of nuclear DNA content was used to estimate ploidy levels of the progenies with results showing that using 3x by 2x breeding approach differing levels of ploidy were achieved [3x (288), 4x (61), 5x (14) and 2x (2)] signifying the predominance of 3x progenies and the presence of 5x and 4x conforming to the possibility of sexual polyploids. Although pollination of Sukali Ndizi can be done all around the year, the seed set both quantity and quality and germination were very poor, necessitating the development of an efficient regeneration protocol for zygotic embryos at varying maturity stages to increase the recovery of hybrids.