Abstract

Cocos nucifera L., is a member of the monocotyledonous family Arecaceae (2n=2x=32) and is the only species of this genus. It is one of the major perennial oil crops distributed throughout the tropics between 20ºN- 20ºS latitude. In spite of being a montotypic species with no known wild relatives, the crop still presents considerable diversity in forms, which are used in the coconut improvement programme. Coconut populations are generally classified into tall and dwarf types based on the relative stature. Both the tall and dwarf types show high variability for morphological characters and for other quantitative traits between the populations as well as within the population. The present study is aimed at understanding whether these variations at the morphological level are reflected by relative variations in their genome size. With this objective, 20 phenotypically different coconut accessions, including 14 tall and 6 dwarf accessions, and of diverse geographic origin, were selected for the studying the genome size by using flow cytometry technique. Nuclei were extracted from young leaves of the 20 selected accessions maintained in the coconut field gene bank at ICAR-CPCRI, Kasaragod. The absolute genome size was computed from the histogram G0/G1 peak (with CV less than 3%) for both coconut and internal reference standard (Pisium sativum 2C= 9.09 pg DNA). Significant differences in DNA content was observed among the accessions studied, with the estimated DNA content ranging from 5.73 pg (Chowghat Orange Dwarf) to 6.25 pg (Guam Tall II). Relative differences in genome size was observed between tall and dwarf accessions, with estimated average genome size of 6.07 pg and 5.89 pg for talls and dwarfs, respectively. Further, tall accessions showed more variation for nuclear DNA content as compared to the dwarfs, irrespective of place of origin, indicating more heterogeneous nature of the tall forms than dwarfs. The results of this study offers leads for better understanding of the intra-specific variation in this important tropical palm, and possibility of manipulation of relative differences in genome size, utilizing bioinformatic tools and coconut genome sequencing data.