Genetic diversity in wild populations of the restinga ecotype of the cashew (Anacardium occidentale) in coastal Piau\xed, Brazil

Juelina O Dos Santos,Cleiton B Bittencourt,Simon J Mayo,Ivanilza M De Andrade

doi:10.1007/s00606-019-01611-4

Juelina O Dos Santos, Cleiton B Bittencourt + Show 2 more

Open Access

https://doi.org/10.1007/s00606-019-01611-4

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Abstract

The cashew, Anacardium occidentale, is a globally important tropical fruit tree, but little is known about its natural infraspecific systematics. Wild Brazilian populations occur in the cerrado biome and coastal restinga vegetation. We investigated whether wild coastal and domesticated populations could be distinguished genetically using inter-simple repeat molecular markers (ISSRs). In total, 94 polymorphic loci from five primers were used to characterise genetic diversity, structure and differentiation in four wild restinga populations and four domesticated ones from eight localities in Piauí state (30 individuals per population). Genetic diversity was greater overall in wild (%P: 57.2%, I: 0.24, He : 0.15) than domesticated populations (%P: 49.5%, I: 0.19, He : 0.12). Significant structure was observed among the eight populations (between-population variance 22%, ΦPT = 0.217, P ≥ 0.001), but only weak distinctions between wild and domesticated groups. Cluster and principal coordinate analyses showed marked genetic disparity in populations. No correlation of genetic and geographical inter-population distance was found (Mantel test, r = 0.02032, P = 0.4436). Bayesian analysis found an eight-group optimal model (ΔK = 50.2, K = 8), which mostly corresponded to sampled populations. Wild populations show strong genetic heterogeneity within a small geographical area despite probable gene flow between them. Within-population genetic diversity of wild plants varied considerably and was lower where extractive activities by local people are most intense (Labino population). The study underlines the importance of wild populations as in situ genetic reserves and the urgent need for further studies to support their conservation.

Highlights

The cashew or caju (Anacardium occidentale L.) is a fruit tree cultivated throughout the tropics but native to South America (Johnson 1973; Mitchell and Mori 1987)
The results indicated that the three wild populations at Pedra do Sal (PS), TU and CA have the greatest within-population genetic diversity, while that at LA is similar to the less diverse populations of domesticated cashew at Cajueiro da Praia (CP) and LU
We judge that our observed genotyping error (6.7%, which compares to the 5% maximum AFLP error rate used by Vašek et al 2017) is unlikely to have affected the optimal 8-group genetic structure or the relative values of the genetic diversity parameters among the wild and domesticated populations

Summary

Introduction

The cashew or caju (Anacardium occidentale L.) is a fruit tree cultivated throughout the tropics but native to South America (Johnson 1973; Mitchell and Mori 1987). It has a significant agronomic role globally, especially for the edible. The hypocarp or pseudofruit is eaten fresh or used to manufacture sweets or pulp for juices and other drinks, and the residue from processing is used as a component of animal feed. Tannins—used widely in industrial applications—are extracted from branches, leaves, the testa of the kernel (seed) and the hypocarp residue (USAID-BRASIL 2006)

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