Creation and evaluation of induced allotetraploids from wild Arachis species expands the genetic reservoir for peanut early leaf spot resistance

Early leaf spot (ELS), caused by Passalora arachidicola, remains one of the most economically important foliar diseases of peanut (Arachis hypogaea), and resistance within the cultivated germplasm is limited. Fungicide applications are commonly used to manage this disease, but this practice increases production costs, the risk of fungicide resistance, and environmental concerns. Wild Arachis species harbor diverse resistance alleles, but their direct use in breeding is constrained by ploidy barriers. In this study, eight induced allotetraploids derived from nine wild Arachis species were produced. Along with their diploid parents, they were evaluated for ELS resistance using in vitro detached leaf bioassays. Disease resistance was quantified using multiple components, including incubation period, lesion number, sporulation, and diseased leaf area. Several allotetraploids-particularly MagDio1, MagKuhl1, MagHoeh1, and ValMicro1-exhibited significantly reduced lesion development, limited sporulation, and slower disease progression compared with cultivated controls. In all cases, induced allotetraploids displayed resistance levels equal to or greater than those of both diploid parents, indicating enhanced resistance following allotetraploidization. Notably, Arachis hoehnei and its derived allotetraploid consistently exhibited strong resistance across disease components, identifying this phylogenetically distinct species as a novel resistance source. These results demonstrate that induced allotetraploids represent peanut-compatible reservoirs of diverse ELS resistance alleles and provide practical resources for breeding programs aimed at developing cultivars with more durable and diversified resistance to early leaf spot.