Genetic dissection of maydis leaf blight resistance in maize through QTL mapping

Maydis leaf blight (MLB) is a major foliar fungal disease of maize causing yield losses of up to 40% under favourable conditions. Developing resistant cultivars is the most sustainable management strategy, requiring the identification of stable resistance loci and a better understanding of the genetic architecture underlying MLB resistance across environments.

A recombinant inbred line (RIL) mapping population of 182 F₉ lines derived from susceptible HKIPC4B and resistant CML 269-1 was evaluated across seven environments (2020-2025) using an augmented block design. Disease severity and percent disease incidence ranged from 2.1 to 8.3 and 23.8-83.8%, respectively, indicating substantial phenotypic variation. Genotyping by ddRAD sequencing generated a linkage map of 6,527 SNPs spanning 2,124.30 cM, identifying 15 QTLs on chromosomes 1, 2, 3, 5, 6, 8, and 10 (LOD 3.0-20.3), explaining 6.2-13.4% of phenotypic variation. Multi-environment analysis detected four stable QTLs exhibiting QTL × environment interactions (QEI) with low QEI effects, indicating consistent expression across environments. Seven significant first-order epistatic interactions were identified, highlighting the complex genetic basis of resistance. A total of 271 candidate and 82 orthologous genes were identified within QTL intervals, including Zm00001eb268770, Zm00001eb268820, and Zm00001eb268800, which co-localized with a major QTL and have previously been associated with MLB resistance.

The identified stable QTLs, epistatic interactions, and candidate genes provide valuable genomic resources for marker-assisted breeding, candidate gene validation, and the development of durable MLB-resistant maize cultivars.