Effects of In Vitro Polyploidization on Agronomic Characteristics and Fruit Carotenoid Content; Implications for Banana Genetic Improvement

Abstract

Bananas (Musa spp.), native to South East Asia, have spread worldwide and are integrated into the diets of millions of people in tropical regions. Carotenoid content varies dramatically between different banana genotypes, providing an opportunity for vitamin A biofortification. Polyploidization is a useful tool for crop improvement with potential to generate new diversity, especially in a polyploid crop like bananas. Ten induced tetraploids generated from six diploid banana genotypes were evaluated for their agronomic attributes and fruit carotenoid content in comparison to their diploid progenitors. Tetraploids had distinct plant morphology, but generally displayed inferior vegetative and yield characteristics with 20% lower bunch weights than their original diploids. Similarly, a 50% decrease in fruit provitamin A carotenoids (α-carotene, 13-cis β-carotene, 9-cis β-carotene, trans-β-carotene) accompanied by a corresponding increase in lutein was recorded in induced tetraploids in comparison to their original diploids. Additionally, all lines were subjected to pollen viability tests to assess their fertility. Pollen viability tests indicated over 70% viability for induced tetraploids and diploid controls, suggesting their possible use in crosses. These findings provide a basis for the application of induced polyploidization in bananas to generate useful genetic material for integration in hybridization programmes aiming to produce vitamin A enriched triploids valuable to malnourished populations.

Keywords: banana genetic improvement; biofortification; carotenoid content; diploid bananas; in vitro polyploidization; pollen viability; vitamin A.

Figure 1

Leaf characteristics of diploid and induced tetraploid banana cultivar Galeo. Pre-flowered plants of diploid (A) and induced tetraploid (B) and mature plants for diploid (C) and induced tetraploid (D) of cultivar Galeo.

Figure 2

Heatmap and hierarchical clustering for agronomic traits in diploid and induced tetraploid bananas. Genotype names on the vertical axis followed by 2x and 4x indicates diploids and tetraploid lines respectively. DF, days to flowering; PHT, plant height; PGT, Plant girth; NSF, number of suckers at flowering; DFM, days to fruit maturity; BWT, bunch weight; NH, number of hands; NF, number of fruits; FLT, fruit length; FC, fruit circumference; FWT fruit weight. Bright blue indicates lowest values while bright red indicates highest values for each trait.

Figure 3

Bunch characteristics of diploid and induced tetraploid bananas. 2x Sowmuk (1A); 4x Sowmuk (1B); 2x AAcv Rose (2A); 4x AAcv Rose (2B); 2x Pisang Madu (3A); 4x Pisang Madu (3B); 2x 25447-S7 (4A); 4x 25447-S7 (4B).

Figure 4

Heatmap and hierarchical clustering for carotenoid traits in diploid and induced tetraploid bananas. Genotype names followed by 2x and 4x indicates diploids and tetraploid lines respectively. AC, α-carotene; TCBC, 13-cis-β-carotene; NCBC, 9-cis β-carotene; TBC, trans-β-carotene; BCE, β-carotene equivalents; pVACs, total carotenoids with vitamin A activity; TC HPLC, total carotenoids determined by HPLC. Bright blue indicates lowest values while bright red indicates highest values for each trait.

Figure 5

TTC stained pollen from diploid (A) and tetraploid (B) banana cultivar Galeo, showing high viability. Magnification 200x.