Could the ploidy level of banana be determined based on stomatal traits

Abstract

Inexpensive and accurate method for verification/determination of ploidy levels of progenies is required due to the production of different euploids and aneuploids in banana breeding. Although, protocols for root-tip chromosome counting or flow cytometry analysis are in vogue in banana, these techniques may be expensive for breeders working with large segregating populations. Therefore, the aim of this study was to assess the overall degree of polymorphism and similarities among stomatal traits and also to examine the reliability of these stomatal traits in 239 banana germplasm for determination of their ploidy levels. Results showed considerable variations/diversity among banana genotypes and all the stomatal traits viz. stomatal density (SD), stomatal length (SL), stomatal width (SD) and stomatal size (SS) were significantly different within the same ploidy level of intra and/or intergenomic hybrids of A and B genome. With increase in ploidy levels, SD significantly decreased from 85.0 (AA) to 25.4 (ABBB) number/mm2 while SS were increased significantly from 705.8 (AB) to 1355.7 (ABBB) µm2 genome. However, the SD ranges overlap among ploidies, more specifically diploids having BB genomes with triploids. A comparison of SS and SD shows that the higher the ploidy, the larger and less numerous were the stomata, the relationship being approximately linear as revealed by scatter plot analysis. However BB diploids, are not likely to be so sharply distinguished from triploids because of its overlapping as revealed by cluster analysis, box plot and descriptive distribution analysis. In general SS is clearly the most reliable index of ploidy than SD as the later was more variable and overlapping with even tetraploids. In conclusion, stomatal characters offer a lead for assessing ploidy in banana though chromosome counts/flow cytometry cannot be entirely eliminated in banana germplasm.