Abstract
Early and late leaf spots (LLSs) are the major foliar diseases of peanut responsible for severely decreased yield in the absence of intensive fungicide spray programs. Pyramiding host resistance to leaf spots in elite cultivars is a sustainable solution to mitigate the diseases. In order to determine the genetic control of leaf spot disease resistance in peanut, a recombinant inbred line population (Florida-07 × GP-NC WS16) segregating for resistance to both diseases was used to construct a SNP-based linkage map consisting of 855 loci. QTL mapping revealed three resistance QTLs for LLS qLLSA05 (phenotypic variation explained, PVE = 7–10%), qLLSB03 (PVE = 5–7%), and qLLSB05 (PVE = 15–41%) that were consistently expressed over multi-year analysis. Two QTL, qLLSA05 and qLLSB05, confirmed our previously published QTL-seq results. For early leaf spot, three resistance QTLs were identified in multiple years, two on chromosome A03 (PVE = 8–12%) and one on chromosome B03 (PVE = 13–20%), with the locus qELSA03_1.1 coinciding with the previously published genomic region for LLS resistance in GPBD4. Comparative analysis of the genomic regions spanning the QTLs suggests that resistance to early and LLSs are largely genetically independent. In addition, QTL analysis on yield showed that the presence of resistance allele in qLLSB03 and qLLSB05 loci might result in protection from yield loss caused by LLS disease damage. Finally, post hoc analysis of the RIL subpopulation that was not utilized in the QTL mapping revealed that the flanking markers for these QTLs can successfully select for resistant and susceptible lines, confirming the effectiveness of pyramiding these resistance loci to improve host-plant resistance in peanut breeding programs using marker-assisted selection.
Highlights
Peanut (Arachis hypogaea L.) is an important row crop rich in oil, protein, vitamins and other micronutrients (Settaluri et al, 2012)
We developed an recombinant inbred line (RIL) population from crossing Florida-07 × GP-NC WS 16 and utilized this population to map QTLs associated with early leaf spot (ELS) and late leaf spots (LLSs) resistance
As for yield data collected from the LLS field trials, no statistical difference was found between the two parental lines across all three years
Summary
Peanut (Arachis hypogaea L.) is an important row crop rich in oil, protein, vitamins and other micronutrients (Settaluri et al, 2012). World peanut production exceeded 100 thousand metric tons in year 2016. The United States is the most efficient peanut producing country and accounts for 6% of world production. Peanut production is threatened by multiple biotic stresses, of which the two foliar fungal diseases, early leaf spot (ELS) caused by Passalora arachidicola (Hori) U. Cercospora arachidicola) and late leaf spot (LLS) caused by Nothopassalora personata Both fungal diseases produce lesions (up to 1 cm in diameter) on peanut leaves, petioles, stems, and pegs (McDonald et al, 1985). In the United States, the most common practice to control both diseases is by frequent fungicide applications; it is not surprising that fungicide sprays to control leaf spot diseases incur the highest cost in disease management (Woodward et al, 2014). Developing and planting ELS and LLS resistant peanut cultivars should reduce the cost of peanut production while simultaneously mitigating the environmental footprint through reduction in pollution from fungicides
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