*1.2. Peanut Germplasms and Core Collection*

Various germplasms with large genetic diversity are excellent resources for peanut breeders to broaden the genetic basis of breeding materials and integrate important alleles related to valuable traits [11]. Diverse germplasms in peanuts have been used to enrich genetic resources, introduce resistance to diseases and pests and, finally, to improve the yield potential through continuous breeding programs.

Recently, effective methods to evaluate and introduce a genetic diversity of germplasm resources have been performed in various studies. Core collections were first defined as a limited set of accessions "representing, with a minimum of repetitiveness, the genetic diversity of a crop species and its wild relatives" [12,13]. The use of core collections has many advantages and they also represent a good starting material for association mapping. Recently, core collections have been established in various crops, including rice [14], wheat [15], maize [16], and *Brassica napus* [17]. The peanut core collections were developed from the US germplasm collection [18], and information on the accessions of the core collection are available at the Germplasm Resource Information Network (GRIN) (https://www.ars-grin.gov).

To promote and improve the utilization of germplasm resources in peanut breeding programs, the peanut mini core collection was established by utilizing the stratification strategy of the United States (US) peanut germplasm resource center [19]. The majority of the accessions in the mini core collection were unrelated individuals, which may be a good starting material for initiating the peanut association study. The purpose of establishing a core or mini core collection for any crop is to promote the efficient and economical use of plant materials by end-users and to identify germplasms with desirable characteristics.

The Oil Crops Research Institute of the Chinese Academy of Agricultural Sciences in China established a core collection with 576 *A. hypogaea* genotypes and a mini core collection with 298 accessions representing the majority of the genetic diversity of cultivated peanut in China. They conducted an association study using the mini core collection, and a total of 89 simple sequence repeat (SSR) alleles were identified as associated with 15 agronomic traits. The results showed that there was a grea<sup>t</sup> possibility to combine association analysis and marker-assisted breeding using the peanut mini core collection [20,21]. The US mini core collection was evaluated and mapped using quantitative trait loci (QTL) for several traits, such as resistance to Tomato spotted wilt virus (TSWV) [21]. In the ICRISAT mini core collection, several candidate regions associated with non-redundant leaf proteins were identified as being related to tolerance to water deficit stress; however, little has been reported regarding these traits in the US germplasms [22].
