Morphology, cross ability, and barcode analysis suggest the monotypic status of Benincasa and distinct genus status for Praecitrullus

Abstract

ABSTRACT Step-wise analysis of core variability in centers of origin and distribution can resolve conflicts over the taxonomic status of any plant species. Ash gourd [Benincasa hispida (Thunb.) Cogn.] and tinda [Praecitrullus fistulosus (Stocks) Pangalo] are vegetables in tropical and subtropical regions of the world. Identification of unique genotypes under Benincasa has led to a situation that requires verifying the monotypic status of this genus. Tinda, also known as round melon, was recommended to be included as a second species in Benincasa. This study tested the hypothesis that Benincasa is monotypic. Morphological evaluation of a mini-core collection comprising 26 ash gourd and 5 tinda entries exhibited variability. Ash gourd and tinda genotypes varied for multiple morphological traits. Cluster analysis differentiated ash gourd and tinda, with nearly 70% dissimilarity. All ash gourd accessions were freely crossable in both directions, ruling out the possibility of any new species. Non-cross-ability of tinda with ash gourd has confirmed its genetic distinctiveness. Nine barcodes distinctly differentiating the genera were identified from the matK and ITS2 loci. With the characteristic morphological traits, non-crossable nature and distinct barcodes that are not shared with any of the members of Praecitrullus, Benincasa should be considered monotypic and a separate genus status retained for Praecitrullus.