Identification of candidate genome regions controlling disease resistance in Arachis

Background Worldwide, diseases are important reducers of peanut (Arachis hypogaea) yield. Sources of resistance against many diseases are available in cultivated peanut genotypes, although often not in farmer preferred varieties. Wild species generally harbor greater levels of resistance and even apparent immunity, although the linkage of agronomically un-adapted wild alleles with wild disease resistance genes is inevitable. Marker-assisted selection has the potential to facilitate the combination of both cultivated and wild resistance loci with agronomically adapted alleles. However, in peanut there is an almost complete lack of knowledge of the regions of the Arachis genome that control disease resistance. Results In this work we identified candidate genome regions that control disease resistance. For this we placed candidate disease resistance genes and QTLs against late leaf spot disease on the genetic map of the A-genome of Arachis, which is based on microsatellite markers and legume anchor markers. These marker types are transferable within the genus Arachis and to other legumes respectively, enabling this map to be aligned to other Arachis maps and to maps of other legume crops including those with sequenced genomes. In total, 34 sequence-confirmed candidate disease resistance genes and five QTLs were mapped. Conclusion Candidate genes and QTLs were distributed on all linkage groups except for the smallest, but the distribution was not even. Groupings of candidate genes and QTLs for late leaf spot resistance were apparent on the upper region of linkage group 4 and the lower region of linkage group 2, indicating that these regions are likely to control disease resistance

Marker-Assisted Selection for Biotic Stress Resistance in Peanut

Marker-assisted selection (MAS) in peanut has lagged behind other major crops. This is due in good part to the genetic bottleneck that occurred at tetraploidization, resulting in a limited amount of molecular variability detectable among accessions of the cultivated species. However, marker maps have been developed from wild species, and, to an increasing extent, the cultivated species using new marker types. It is expected that, with the increase in number of simple sequence repeat (SSR) markers and development of single nucleotide polymorphism (SNP)-based markers, there will be greater use of MAS in both interspecific and cultivated accession crosses. MAS has already proven itself to be useful in developing cultivars possessing resistance to the root-knot nematode, and is being used for selection for resistance to late leaf spot and rust, as well as for the high-oleic-acid trait

The genome sequences of Arachis duranensis and Arachis ipaensis, the diploid ancestors of cultivated peanut

Cultivated peanut (Arachis hypogaea) is an allotetraploid with closely related subgenomes of a total size of ∼2.7 Gb. This makes the assembly of chromosomal pseudomolecules very challenging. As a foundation to understanding the genome of cultivated peanut, we report the genome sequences of its diploid ancestors (Arachis duranensis and Arachis ipaensis). We show that these genomes are similar to cultivated peanut's A and B subgenomes and use them to identify candidate disease resistance genes, to guide tetraploid transcript assemblies and to detect genetic exchange between cultivated peanut's subgenomes. On the basis of remarkably high DNA identity of the A. ipaensis genome and the B subgenome of cultivated peanut and biogeographic evidence, we conclude that A. ipaensis may be a direct descendant of the same population that contributed the B subgenome to cultivated peanut