Identification of major QTL for seed number per pod on chromosome A05 of tetraploid peanut(Arachis hypogaea L.)

The inheritance of pod-and seed-number traits(PSNT) in peanut(Arachis hypogaea L.) is poorly understood. In the present study, a recombinant inbred line(RIL) population of 188 lines was used to map quantitative trait loci(QTL) for number of seeds per pod(NSP),number of pods per plant(NPP), and numbers of one-, two-, and three-seeded pods per plant(N1 PP, N2 PP, and N3 PP) in four environments. A total of 28 consensus QTL and 14 single QTL were identified, including 11 major and stable QTL. Four major and stable QTL including qN3 PPA5.2, q N3 PPA5.4, qN3 PPA5.5, and qN3 PPA5.7 each explained 12.3%–33.0% of phenotype variation. By use of another integrated linkage map for the A5 group(hereafter referred to as INT A5 group), QTL for PSNT were located in seven intervals of 0.73–9.68 Mb in length on chromosome A05, and candidate genes underlying N3 PP were suggested. These findings shed light on the genetic basis of PSNT. Major QTL for N3 PP could be used as candidates for further positional cloning.

Phenotypic identification of peanut germplasm for resistance to southern stem rot

Southern stem rot,caused by Sclerotium rolfsii Sacc.,is a destructive soil fungal disease of peanut in China and other countries.To evaluate resistant germplasm,a total of 256 peanut accessions were investigated on their resistance to southern stem rot in 3 environments by artificial inoculation.Variance analysis indicated that disease index was significantly influenced by environment,genotype and genotypeenvironment interactions.Peanut accessions of var.vulgaris type exhibited higher resistance to southern stem rot.Disease index was significantly negatively correlated with linoleic acid content,while positively correlated with oleic acid content.Six resistant accessions were identified,including Hua 28,Shandongzai,ICG 6326,Quanhua 7,Quanhua 9 and Guihua 836,with their disease indexes under 40 and mortality were less than 30%in the three environments.The identified resistant accessions showed the great potential to be applied in resistant peanut breeding,and would be good genetic resources for enhancing the resistance to southern stem rot.

Genetic diversity of atoxigenic Aspergillus flavus isolates from peanut kernels in China

Aflatoxin contamination in peanuts is a major threat to public health, especially in tropical and subtropical regions of the world. Recently, the use of atoxigenic Aspergillus flavus strains as biological control agents prove to be effective in reducing aflatoxin contamination in crops. A total of 208 atoxigenic A. flavus isolates, collected from peanut kernels, were grouped into 7 deletion patterns by quadruplex PCR products of nor-1, ver-1, aflR and omtA genes. 49 SNPs, found in 1254 bp fragment of omtA gene, showed genetic variation of omtA among different A. flavus isolates. These isolates were assigned to either MAT1-1 type or MAT1-2 type with primers for each MAT locus. Thus, rich genetic diversity was found in the atoxigenic A. flavus isolates of peanut in China. The results indicated that quadruplex PCR would be an effective method for rapid screening of atoxigenic isolates with gene deletion in aflatoxin biosynthetic cluster.

Biocontrol potential of reducing aflatoxin contamination by an atoxigenic strain of Aspergillus flavus. isolated from peanut

An Aspergillus section/Zam isolate （ NAFFHB396） was isolated from a peanut kernel. It was identified as Aspergillus flavus based on morphology and molecular characteristics. It produced yellow to green - colored conidia on CYA medium and colonies with bright orange in color on AFPA medium. NAFFHB396 was grouped with A. flavus NRRL21882 and NRRL3357 by phylogenetic analysis of partial calmodulin sequence data. It was found that 12 genes were absent in aflatoxin gene cluster in NAFF- HB396. HPLC result further showed that it was an atoxigenic isolate. Co - inoculation of NAFFHB396 with a high aflatoxin producer AF2202 at the ratio of 1：1 both on CYA medium and peanut kernel resul-ted in reduction of aflatoxin production by 88.7% and 99. 8% respectively. These results suggested that the atoxigenic NAFFHB396 obtained in this study had a great potential to be a biocontrol agent to reduce aflatoxin contamination of peanut in China.

Progress on genetic and genomic research for enhanced oil content and quality in peanut

Peanut or groundnut （ Arachis hypogaea L. ） is an important source of vegetable oil in the world. Genetic enhancement for high yield and high oil content has greatly contributed to enhanced pro-ductivity of peanut and increased supply of peanut oil. Further improving oil content and quality of peanut is still crucial for increasing productivity of arable land and market competitiveness of peanut oil. Based on investigation among the peanut germplasm accessions including wild Arachis species, the oil content could be as high as 65%. Heterosis has been observed for oil content in hybrids derived from diverse crossing parents. Segregates with enhanced oil content have been obtained by pyramiding different genes or alleles with major and minor additive effects. Improved testing techniques for oil content in breeding lines with reduced cost have accelerated breeding progress for high oil content. SSR markers associated with oil content have been identified by association and linkage analysis. The stability of oil content in peanut across seasons and locations is highly associated with cold tolerance, high nutrition efficiency and drought tolerance. Recent progress on improving fatty acids in particular marker assisted backcrossing breeding has contributed to higher quality peanut oil and other products. High oil peanut lines with im-proved resistance to aflatoxin production have been developed. The wild Arachis species would be of great value for peanut breeding in increasing oil content.

Development and validation of simple sequence repeat markers from Arachis hypogaea transcript sequences

Simple sequence repeats(SSRs) are important molecular markers for assessing genetic diversity in Arachis hypogaea L. and many other crops and constructing genetic linkage maps for important agricultural traits. In this study, 29,357 potential SSRs were identified in 22,806 unigenes assembled from A. hypogaea transcript sequences. Of these unigenes, 1883 and 4103 were annotated and assigned in Kyoto Encyclopedia of Genes and Genomes Orthology and Eukaryotic Orthologous Groups databases, respectively. Among the SSR motifs, mono-(19,065; 64.94%) and trinucleotide(5033; 17.14%) repeats were the most common, and the three most dominant motifs were A/T(18,358; 62.54%), AG/CT(2804;9.55%), and AAG/CTT(1396; 4.76%). Polymerase chain reaction(PCR) primer pairs were designed for 4340 novel SSR markers and 210 new SSRs were validated using 24 A. hypogaea varieties. Of the 210, 191(91%) yielded PCR products, with 37(18%) identifying polymorphisms. The 37 polymorphic SSR markers detected 146 alleles(2–10 alleles per locus), and the average polymorphic information content was 0.403(with a range of 0.077 to0.819). The new SSRs enrich the current marker resources for A. hypogaea and may also be useful for genetic diversity analysis, functional genomics research, and molecular breeding.

Diversity characterization and association analysis of agronomic traits in a Chinese peanut (Arachis hypogaea L.) mini-core collection

Association mapping is a powerful approach for exploring the molecular basis of phenotypic variations in plants. A peanut （Arachis hypogaea L.） mini-core collection in China comprising 298 accessions was genotyped using lo9 simple sequence repeat （SSR） markers, which identified 554 SSR alleles and phenotyped for 15 agronomic traits in three different environments, exhibiting abundant genetic and phenotypic diversity within the panel. A model-based structure analysis assigned all accessions to three groups. Most of the accessions had the relative kinship of less than o.05, indicating that there were no or weak relationships between accessions of the mini- core collection. For 15 agronomic traits in the peanut panel, generally the Q ＋ K model exhibited the best performance to eliminate the false associated positives compared to the Q model and the general linear model-simple model. In total, 89 SSR alleles were identified to be associated with 15 agronomic traits of three environments by the Q＋K model-based association analysis. Of these, eight alleles were repeatedly detected in two or three environments, and 15 alleles were commonly detected to be associated with multiple agronomic traits. Simple sequence repeat allelic effects confirmed significant differences between different genotypes of these repeatedly detected markers. Our results demonstrate the great potential of integrating the association analysis and marker-assisted breeding by utilizing the peanut mini-core collection.