Genetic characterization of promising high-yielding cashew (Anacardium occidentale L.) cultivars from Côte d'Ivoire

Abstract

Description of the subject. Cashew was introduced to Côte d'Ivoire in 1951 to control erosion and reforest cutover lands. From 1972 to 1980, natural forest plantations were converted to fruit orchards and were supplemented by the ‘Jumbo’ cashew variety imported from Brazil. Germplasm expeditions conducted in 2010 and 2014–2015 identified 209 high-yielding cultivars in the major cashew growing areas of Côte d’Ivoire. Although the morphological characteristics of these cultivars have been assessed, little is known about the genetic diversity and genetic structure of the germplasm collection. Objectives. The objective of the study was to evaluate the genetic diversity of high-yielding cashew cultivars for better use in breeding programs. Method. We performed DNA isolation using Qiagen DNeasy Plant Mini Kits and PCR analysis with 18 SSR markers. Results. We identified the first two introduced populations of cashew in Côte d’Ivoire. The average allelic richness is 3.56 (± 1.45) alleles per locus, the fixation index (FIS) indicates an overall heterozygosity deficit of 0.332 (± 0.076), and the average population differentiation (FST) is 0.014 (± 0.004). Much of the total genetic variability occurs at the intra-population level (98.6%), compared to only 1.4% variability attributable to differences between populations. Average value of gene flow is 22.528. Conclusions. Gene flow within cashew populations maintains high intra-population genetic diversity. This flow rate reflects a long-term exploitable genetic variability for use in selection and conservation.

East Timor as an important source of cashew (Anacardium occidentaleL.) genetic diversity

“…In Brazil, wild Brazilian populations of cashew were studied ( Dos Santos et al, 2019 ), and the genetic diversity in wild populations was higher than in domesticated ones, despite a weak distinction between wild and domesticated groups and with no correlation between genetic and geographical interpopulation distance. In Cô te d’Ivoire, cashew genetic diversity was studied using SSRs and the resultsnrevealed an overall heterozygosity deficit and a high intra-population genetic diversity among the screened cashew populations ( Kouakou et al, 2020 ), which is in accordance with the AMOVA results of this study where the most genetic diversity was depicted within populations. The results obtained from this study also agree with a recent study from Burkina Faso, where a substantial amount of genetic diversity was observed across the 18 cashew accessions screened with four SSRs ( Moumouni et al, 2022 ).…”

“…Considering the 11 populations studied from East Timor, population differentiation ( F ST = 0.129, Table 5 ) was relatively moderate in comparison to a previous study of cashew trees in Côte d’Ivoire ( Kouakou et al, 2020 ) where a low differentiation was indicative of a common origin. However, moderate differentiation could also be associated with the lower number of molecular markers used in this study (12 SSRs vs 18 SSRs in Kouakou et al, 2020 ).…”

“…Less observed diversity in Viqueque is likely because cashew orchards are less frequent in the Viqueque district compared with the Baucau and Manatuto districts, where several orchards have been planted over the last 20 years. The populations analyzed in this study might reflect long-term genetic diversity that can be exploited in a breeding program to improve yield and nut quality ( Kouakou et al, 2020 ). Moreover, identifying trees with high allelic richness is necessary for conserving the cashew germplasm ( Bataillon, David & Schoen, 1996 ).…”

“…Most studies on this topic were performed in the top cashew-producing countries and with different molecular markers, namely microsatellites (SSRs, simple sequence repeats) and RAPDs (random amplified polymorphic DNA). For example, the genetic diversity of cashew accessions have been characterized in Côte d’Ivoire ( Kouakou et al, 2020 ), Nigeria ( Aliyu & Awopetu, 2007 ), India ( Archak et al, 2009 ), Tanzania ( Mneney, Mantell & Bennett, 2001 ), Malawi ( Chipojola et al, 2009 ), and Brazil ( Dos Santos et al, 2019 ). Overall, these studies highlight the narrow genetic diversity of cashew accessions when compared to Brazil, the native country of origin of cashew trees, where a higher diversity was observed.…”

“…Studies on the cashew germplasm have mostly been done in major cashew-producing countries ( e.g. , Côte d’Ivoire ( Kouakou et al, 2020 ), Nigeria ( Aliyu & Awopetu, 2007 ), India ( Archak et al, 2009 ), Tanzania ( Mneney, Mantell & Bennett, 2001 )) and a narrow genetic diversity has been observed. However, in countries more recent to commercial cashew production with low or no presence in international cashew markets, the genetic diversity of cashew trees remains to be discovered.…”