Morphological index and flow cytometry as tools for discriminating Musa L. germplasms from Northeast India for estimation of ploidy and genome composition

Abstract

Genome characterization is an essential aspect for understanding the origin and physiological adaptation of any species. The size of the genome, its constitution, and ploidy level provide the valuable information on the taxonomic relationship, which is further utilized in genetic crop improvement program concentrating on traits of interest. Musa sp., also known as the banana/plantain, is a fruit and vegetable that is grown all over the world. Because of the inter- and intra-specific hybridization with their wild diploids, the majority of banana cultivars are triploid and seedless in nature. Today's banana cultivars have different genome sizes and ploidies as a consequence, which contributes to their unique shape and climate adaptation. However, limited information is available on the genomic resources of wild and cultivated bananas commonly found in the northeastern region of India. In this study, we performed the morphological characterization, genome size estimation, and ploidy analysis of 16 Musa germplasm collected from northeast India. Morphological characterization and flow cytometry-based (FCM) 2C DNA content revealed significant variation in the ploidy level among the collected Musa germplasms. Further, the present result revealed that the morphological scoring based on ploidy and genome composition was not always consistent with the flowcytometry DNA content data. The neighbor-joining (NJ) tree based on morphology scoring of Musa sp. var. fushrey jhapari (NBRI-0020) clustered into the diploid group (Group II), however, it was not a diploid, which confirmed in flow cytometry data-based NJ tree (Group I). It is further revealed that the Musa sp. var. fishery jhapari (NBRI-0020) had a total morphological score of 54, which did not fall under any genome composition category, however, it showed relatively closer to diploid group in the morphology-based NJ Tree. In the contrary, Musa balbisiana var. jungli kol (NBRI-0027) and Musa sp. var. jungli kol (NBRI-0028) were found to be diploid in flow cytometry data, while those on morphology scoring were categorized as triploid, thereby flow cytometric data must be supplemented with morphology-based data for an accurate genome composition categorization. Our findings in this present study provides valuable insight into the composition of wild and cultivated Musa genome. In most of the cases (~ 68.75%; 11 out of 16) of Northeast India Musa genotypes, the morphology scoring-based genome composition did not match with FCM-based genome composition, indicating the morphology-based genome composition of Musa genotypes from North-East India is not straightforward and accurate. This present data on Musa genotypes of Northeast India will supplement the morphological traits-driven breeding program for banana genetic improvement. Furthermore, our findings shed light on the genome evolution of bananas in north-east India which is still remained unexplored because of its complex evolutionary processes.