Genetic Resources of Groundnut

Abstract

Groundnut or peanut is one of the major oilseeds and food crops cultivated globally. This oilseed can be directly consumed as a foodstuff, is a rich source of oil, protein and carbohydrates and other nutrition like tocopherol, niacin and folic acid; mineral components like Cu, Mn, K, Ca and P; dietary fibres, flavonoids, phytosterols like resveratrol, beta-sitosterol; and phenolic acids. The cultivated groundnut Arachis hypogea is a segmental amphidiploid (4x = 40), and cytogenetic and molecular evidences suggest that the origin of cultivated groundnut was from a hybridization of two diploid wild species Arachis duranensis (AA) and Arachis ipaensis (BB). Eighty-three species of Arachis have been described and most of species in the genus Arachis are diploid with x = 10 (2n = 20), while a few aneuploid (2n = 2x = 18) and tetraploid (2n = 4x = 40) species are also reported, and new taxa continue to be discovered. Higher yield has been the most frequently targeted trait in the breeding programmes, and the enhanced yield attained in the Indian cultivars has been attributed to the improvement in seed size, seed weight, and number of pods per plant. The other trait which have been in focus is tolerance/resistance to diseases and drought, which have been the major production constraints. Improving quality of the produce also is now being taken up in addition to enhancement of yield. Early leaf spot (ELS; caused by Cercospora arachidicola), late leaf spot (LLS; caused by Phaeoisariopsis personata) and rust (caused by Puccinia arachidic) are the most prevalent foliar fungal diseases in groundnut. Among the viral diseases reported in groundnut from India, peanut bud necrosis virus (PBNV), tobacco streak virus (TSV), peanut mottle virus (PeMoV), and Indian peanut clump virus (IPCV) are the economically important. Among nematodes, peanut root-knot nematode (Meloidogyne spp.) and the root-lesion nematode (Pratylenchus brachyrus) are prominent. The breeding programmes across the groundnut growing countries mainly focus on these.

Due to the tetraploid nature of the crop and the complexity of the genome, marker development in cultivated groundnut has been in a slow pace. A good amount of genomic resources for groundnut has been added during the last 15 years. Several mapping populations have been prepared and the markers were mapped into genetic maps using these populations and used to understand the genome architecture and to identify QTLs for the economically important traits. The majority of QTLs reported are for foliar fungal diseases followed by oil quality and stem rot resistance. Though several reports on marker associations are available, utilisation of marker-assisted breeding is very meagre.

The availability of the draft genomes have opened up the large-scale genome-wide discovery of makers and the development of an58K Axiom_Arachis SNP array By the advent of the rapid sequencing tools and assembly tools, a good number of transcripts were assembled and analysed in detail.

In India alone more than 200 varieties have been developed so far for commercial cultivation. Several programmes in genomics-assisted breeding are underway and may come out with improved cultivars which can be grown under different production constraints without compromising yield and quality.