Morphological, cytogenetic and genotypic differences between spicata and ordinary tall coconut (Cocos nucifera L.)

Cocos nucifera L. coconut is an economically important crop throughout the humid tropics for food, oleochemicals and as a source of uncontaminated sweet beverage. Palms that contain morphologically different inflorescences are referred to as spicata coconut and are considered as a special form of the variety Typica. A number of differences exists in the spicata inflorescence, when compared to that of the ordinary tall variety. The main difference in the spicata inflorescence is the suppression of male flowers on the inflorescence and the presence of a large number of female flowers compromising the former. Based on the type of branching of the inflorescence and the structure of the male and female flowers, different spicata types can be identified. The objective of the present study is to document the different spicata types of coconut and to investigate whether there exists karyotypic differences between the different types of spicata and the ordinary tall coconut. The genomic composition of the root tip cells of spicata seedlings was studied using the chromosome squash technique. The squash method performed on root tip cells obtained from both in vivo as well as in vitro grown seedlings using aceto-carmine showed that spicata consists of cells of the normal chromosome compliment of coconut 2n=32 and cells with an aneuploid chromosome compliment varying from 18-24. Length measurements of the chromosome compliment in diploid spicata cells and ordinary tall coconut showed similar length categories. Further studies are necessary to differentiate the lengths accurately. However, an accurate measurement of the DNA content of the diploid and aneuploid cells obtained using a Flow Cytometer indicated that the ratio between the relative DNA contents of diploid to aneuploid cells in spicata ranged from 1:0.5 to 1:0.6. Thus, spicata can be considered as a mutation of ordinary tall coconut.

Keywords: Chromosome, coconut (Cocos nucifera L.), cytology, flow cytometry, spicata  

doi:10.4038/jnsfsr.v36i1.138

Journal of the National Science Foundation of Sri Lanka 36 (1) 103-108