Cytotaxonomic investigations to assess diversity and evolution in Amorphophallus Blume ex Decne. (Araceae)

Abstract

Karyomorphological studies in twenty five accessions of Amorphophallus collected from four biogeographic zones of India comprising of seven wild species and 18 morphotypes and wild relatives of A. paeoniifolius revealed differences in chromosome numbers. Three chromosome numbers viz., 2n = 28 for all the A. paeoniifolius accessions, A. dubius, A. smithsonianus and A. sylvaticus; 2n = 26 for A. bonaccordensis, A. hohenackeri and A. commutatus; and 2n = 3 × = 39 for A. bulbifer were recorded. Based on karyological characters, a scheme for the evolution of chromosome number in the species of Amorphophallus was framed. Zarco’s asymmetry indices revealed that the accessions T2 (A. bonaccordensis) and T3 (A. smithsonianus) are the more evolved species in terms of karyotype symmetry. According to the classification of Stebbins, A. bonaccordensis included in 3B category was the most asymmetrical and hence considered as most evolved. Amorphophallus paeoniifolius var. campanulatus with A1 = 0.40–0.43 appeared to be more evolved than A. paeoniifolius var. paeoniifolius based on Zarco’s asymmetry indices. Slight differences observed in the A1 values (0.1714–0.37) in the accessions of A. paeoniifolius var. paeoniifolius demonstrate the close relationship of the accessions. Among the A. paeoniifolius accessions, TF% varied between 35.34 % (GJ) to 43.6 % (K3-1) with TF% of 37.64 in T10. Taxa with asymmetric karyotype tend to have low TF% and accordingly cv. Gajendra (GJ) and cv.karunaikizhangu (T10) (both A. paeoniifolius var. campanulatus) having low TF% can be considered as highly evolved among the A. paeoniifolius accessions. UPGMA clustering based on five karyotypic parameters namely total chromosome length (TCL), average chromosome length (ACL), chromosome number, TF% and ratio of longest chromosome (LC) to shortest chromosome (SC) of the complement revealed two principal clusters at a Euclidean distance of 1.3 and such clustering pattern is in tune with the morphological data which leads to make a valid assumption that A. dubius may be the immediate ancestor of cultivated forms.