Date: 24 Aug 2011

Groundnut

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Abstract

Groundnut (Arachis hypogaea L.) primarily considered as an oilseed crop in developing countries is an important source of protein and also serves as fodder for livestock industry. The genus Arachis consists of 80 annual and perennial wild species which include diploids and tetraploids distributed in nine sections. All the species are occurring in South America east of the Andes, south of the Amazon, north of La Plata and from northwest Argentina to northeast Brazil. Cultivated groundnut is a segmental allopolyploid having the genomic constitution of AABB, which is believed to be originated through single hybridization between two diploid species. Cultivated groundnut is broadly classified into two subspecies (hypogaea and fastigiata) and six botanical types (hypogaea, hirsuta, fastigiata, peruviana, aequatoriana and vulgaris). Two botanical types viz. vulgaris and hypogaea occupied major groundnut growing area. A total of 14,310 genotypes including local land races, breeding lines, and genetic stocks collected across the world are being maintained at International Crop Research Institute for Semi-Arid Tropics (ICRISAT), India. The breeders hesitate to utilize the germplasm directly because of lack of knowledge about the germplasm, unavailability of descriptive characters, and evaluation methods. Hence, core and minicore subset were developed for multiple environmental condition, earliness, nutritional quality, and Sclerotinia blight resistance. Various biotic (foliar and fungal diseases, bacterial and viral diseases, nematodes, Aspergillus and insects) and abiotic stresses (drought and salinity) limits groundnut production. Concerted efforts have been made to tackle the stresses by developing improved cultivars of groundnut with inbuilt resistance/tolerance along with enhanced nutritional quality to meet the demand of farmers, traders, and consumers. Earlier objectives were fulfilled through conventional breeding approaches such as mass selection and pure line selection. Later both intra- and interspecific hybridization has been made extensively to fulfill the goals by following pedigree and backcross method of breeding. Mutation breeding also played a significant role in developing several promising high-yielding cultivars in India and China. Although cultivars with inbuilt resistance were developed through conventional approaches, resistance is always linked with poor pod and kernel features which are very difficult to break. Biotechnological approaches such as marker assisted selection (MAS) and genetic transformation helps to develop ideal groundnut cultivar with inbuilt resistance and improved pod and kernel features and pave the way to introgress genes from incompatible species. SSR markers are widely used for genotyping, construction of linkage map, and for MAS due to its codominant and easy to detect nature from a small amount of DNA. QTLs for pod and seed traits were identified for yield improvement. Markers were also identified for resistance to foliar diseases, Sclerotinia blight, aflatoxin, nematode, and drought. Both conventional breeding and MAS makes the selection more stringent and helps achieve the goal. Transgenic groundnut was successfully developed by integrating a nonheme chloroperoxidase (cpo-p) gene which inhibits Aspergillus flavus hyphal growth which in turn reduces aflatoxin contamination. Introduction of cry1A(c) gene in groundnut protects the crop from lesser cornstalk borer damage. The transgenic groundnut can also be utilized as a donor parents in conventional breeding for developing cultivars for resistance to bacterial and fungal diseases.