Advances in genomics of cashew tree: molecular tools and strategies for accelerated breeding

Cashew is the second most important edible tree nut crop after almonds. It is cultivated in more than 30 countries due to economic and nutritional importance. The global demand for cashew is increasing rapidly every year. Like in other perennial tree species, genetic improvement of cashew by traditional breeding is slow and unpredictable due to the long juvenile phase, high degree of heterozygosity, lack of juvenile-mature traits correlations and large size of the mature plant. Additionally, most of the yield and agronomic traits are genetically complex which complicate its breeding. Recently, the next-generation sequencing (NGS) and high-throughput genotyping technologies have expedited the pace of development of genomic tools and resources for genomics-orphan crops like cashew. The genomics advancements allow designing novel molecular breeding technologies with the potential for enhancing genetic gains and accelerating crop improvement, which is of utmost importance in the breeding of long juvenile species like cashew. In this review article, we describe the breeding objectives, advances in construction of linkage map, QTL dissection and development of genomic sequence resources in cashew. It is followed by a description of designing different genomics-based tools and strategies for accelerating the cashew breeding to quickly develop superior cultivars.