Genetic Variation among Varieties, Wild Species and Related Genera of Arecanut (Areca catechu L.) as Revealed by Microsatellite Markers

Studies on genetic diversity of crops are crucial for germplasm conservation and crop improvement programmes. Arecanut (Areca catechu L.) is one of the plantation crops that have been in cultivation since time immemorial in tropical regions of the world. In this investigation, molecular characterization and genetic diversity analysis was carried out among 20 arecanut genotypes comprising of 16 cultivated types (including 13 cultivated varieties, two dwarf hybrids and a natural mutant), two wild species (Areca triandra and Areca concinna) and two other genera (Normanbya normanbyii and Actinorhytis calapparia), maintained in the National Arecanut Gene Bank, Vittal, Karnataka State, India, by employing eight simple sequence repeat (SSR) markers. A total of 45 alleles were detected with most of the markers revealing five alleles or more. The number of alleles at each locus varied from 3 (AC07 and AC08) to 8 (AC23) with a mean of 5.62 alleles per locus. The polymorphism information content (PIC) value, which is a measure of polymorphism for a marker locus, varied from 0.46 (AC08) to 0.84 (AC01) among the SSR markers loci, the average being 0.70. The effective number of alleles per locus (Ne) ranged from 1.28 to 3.11 with a mean of 2.31. The marker AC07 had the lowest effective number of alleles per locus and the marker AC29 had the highest numbers of effective alleles. Shannon’s Information Index ranged from 0.43 (AC07) to 1.33 (AC23) with a mean of 0.97. The observed heterozygosity (Ho) values ranged from 0.25 to 1.00 with an average of 0.73. The expected heterozygosity (He) values ranged from 0.22 to 0.69 with an average of 0.54. The degree of genetic differentiation among the subpopulations (FST) ranged from 0.11 (AC06) to 0.66 (AC01) with a mean of 0.32. The gene flow (Nm) values ranged from 0.12 (AC01) to 1.96 (AC06) with a mean gene flow value of 0.52. The lowest gene flow value was observed in the marker AC01 and the highest gene flow was exhibited by AC06. The dendrogram constructed using similarity coefficient values, by following the Unweighted Pair Group Method with Arithmetic Mean (UPGMA), formed two major clusters with cluster I consisting of all the 16 cultivated varieties and 2 wild species, viz., Areca triandra and Areca concinna and the second major cluster comprised of related genera viz., Normanbya normanbyii and Actinorhytis calapparia. The highest genetic similarity was observed between the cultivated varieties, Kahikuchi and Mohitnagar and Nalbari and Sumangala, and the lowest similarity value of 0.33 was found between the related genera, Normanbya normanbyii, and the cultivated variety, Sreemangala.