Development of DNA markers for Slmlo1.1, a new mutant allele of the powdery mildew resistance gene SlMlo1 in tomato (Solanum lycopersicum)

Reductions in growth and quality due to powdery mildew (PM) disease cause significant economic losses in tomato production. Oidium neolycopersici was identified as the fungal species responsible for tomato PM disease in South Korea in the present study, based on morphological and internal transcribed spacer DNA sequence analyses of PM samples collected from two remote regions (Muju and Miryang). The genes involved in resistance to this pathogen in the tomato accession 'KNU-12' (Solanum lycopersicum var. cerasiJarme) were evaluated, and the inheritance of PM resistance in 'KNU-12' was found to be conferred via simple Mendelian inheritance of a mutant allele of the PM susceptibility locus Ol-2 (SlMlo1). Full-length cDNA analysis of this newly identified mutant allele (Slmlo1.1) showed that a 1-bp deletion in its coding region led to a frameshift mutation possibly resulting in SlMlo1 loss-of-function. An alternatively spliced transcript of Slmlo1.1 was observed in the cDNA sequences of 'KNU-12', but its direct influence on PM resistance is unclear. A derived cleaved amplified polymorphic sequence (dCAPS) and a high-resolution melting (HRM) marker were developed based on the 1-bp deletion in Slmlo1.1, and could be used for efficient marker-assisted selection (MAS) using 'KNU-12' as the source for durable and broad-spectrum resistance to PM.