Analysis of absolute nuclear DNA content reveals a small genome and intra-specific variation in Cashew (Anacardium occidentale L.), Anacardiaceae

There are scanty data on genome size of Anacardiaceae, and none has been reported for cashew, Anacardium occidentale till date. This study aimed at determining the absolute nuclear DNA content (genome size) that could facilitate research into bio-systematics, genomics and genetic improvement of this important tropical tree crop species. Here, isolated nuclei of preparations from 43 cashew accessions selected across five growing regions were flow cytometrically analyzed for genome size determination using Solanum lycopersicum var. Stupicke with a genome size of 1.96 pg/2C as an internal reference standard.

Mean genome size was significantly different (P<0.01) across the 43 cashew accessions suggesting intra-specific variation (about 3.6% coefficient of variation) for absolute nuclear DNA content in this species, but with no evidence of endopolyploidy or endoreduplication. Flow cytometric analysis data presented here showed that absolute genome size of cashew is about 0.857 pg/2C (419 Mb/1C). However, there was a slight gradual increment in genome size from south to north gradient across sampled populations. The data also showed significant correlation (r=0.368, P<0.01) between nuclear DNA content (genome size) and phenotypic trait, nut weight. The results obtained here confirmed relatively small genome size in this tree species, almost twice genome size of diploid Arabidopsis thaliana but slightly lower than mango, Mangifera indica, a close relative in Anacardiaceae. Similarity in genome size between Mangifera indica and Anacardium occidentale could be a further proof of genetic relatedness between these two important species of Anacardiaceae.