Identification And Evaluation Of Peanut Genotypes With Disease Resistance Through Core Collection

Peanut (Arachis hypogaea L.) is an important oil and cash crop worldwide. It is also an important resource of plant oil and protein. Peanut production, consumption and export in China ranked first in the world, However, bacterial wilt and aflatoxin contamination have greatly impeded the development of peanut industry. Therefore, peanut germplasm resistant to aflatoxin contamination and bacterial wilt are in prerequisite both for breeding program and for production. The core collection has been well accepted as a useful way to improve the efficiency of crop germplasm evaluation and utilization. It contains a subset of accessions from the entire collection that captures most of available genetic information. The information derived from the core collection can be used for efficient utilization of the entire collection. The Chinese core collection of peanut is based on germplasm collected from various ecological regions in China and from some foreign contries. ICRISAT mini core collection is established based on the germplasm in international germplasm resource bank. In the present study, systematic evaluation for resistance to bacterial wilt and aflatoxin contamination in the two core collections was carried out. Several genotypes with resistance to bacterial wilt and aflatoxin contamination were identified. The identified resistant germplasm lines were evaluated based on morphological characters and SSR profiles. The major results are as follows.1. A total of 561 accessions of Chinese peanut core collection and 155 accessions of ICRISAT mini core collection were evaluated. Fifteen lines resistant to Aspergillus flavus invasion and 8 lines resistant to aflatoxin production were identified, which included 8 accessions from Chinese peanut core and 15 accessions from ICRISAT mini core. Sixteen lines resistant to bacterial wilt including 11 accessions from Chinese peanut core and 4 from ICRISAT mini core were identified out. Longxiwan (var. hypogaea), ICG6375 (var. vulgaris) and ICG2019 (var. vulgaris) not only had the resistance to aflatoxin production, but also had certain resistance to Aspergillus flavus invasion. The ratio of peanut genotypes resistant to Aspergillus flavus invasion and aflatoxin production of ICRISAT mini core were higher than those of Chinese peanut core collection respectively. In the other hand, the percentages of genotypes with Aspergillus flavus invasion resistance in var. hypogaea, accessions resistant to aflatoxin production in var. fastigiata and accessions resistant to bacterial wilt in var. hirsuta were relatively high compared to other botanical types. It is proved for the first time that the core collection is effective for screening peanut resources resistant to aflatoxin contamination and bacterial wilt.2. Genetic diversity in the resistant peanut selections was evaluated based on morphological traits. The results indicated that the genetic background of Chinese core collection and ICRISAT mini core collection was quite different. In most cases, Chinese resistant peanut lines and ICRISAT lines clustered together seperately. The pod and seed in the genotypes resistant to A. flavus invasion and aflatoxin production were comparatively small. The shelling percentage of genotypes resistant to bacterial wilt was relatively higher compared with the susceptible ones. Genotypes Shengxian Xiaohongmao resistant to bacterial wilt and 51002-6 and ICG2019 resistant to aflatoxin production with elite agronomic traits were identified. 3. Genetic diversity among the resistant genotypes identified was also evaluated based on SSR approach. Similar to the results obtained from morphological analysis, the resistant genotypes from China and from ICRISAT clustered seperately. The peanut genotypes were divided into different groups based on SSR, which was in accordance with the hierarchy classification of peanut. The greatest genetic distance was deteced between aflatoxin production resistant accession ICG6375 (var. vulgaris) and bacterial wilt resistant Fuchuan Dahuasheng (var. hirsuta), with a diversity index as 0.63. ICGV87281 and ICG4749 with resistance to aflatoxin invasion were identified for the first time, having wide genetic distance with high yielding cultivars such as Zhonghua 5, Zhonghua 6 and Zhonghua 12, and can be used for broadening the genetic background for peanut improvement.4. Based on PCR primers designed according to the conserved NBS-LRR domains of the disease resistance genes, one RGA probably associated with the resistance to aflatoxin from genomic DNA of 6 different resistant/susceptible peanut was obtained. Seven cDNA fragments probably correlated with resistant to bacterial wilt were obtained by cDNA-AFLP.