Genetic Mechanisms Underlying Nuclear Male-sterility in Squash

Commercial deployment of male sterility is highly valued as a tool for efficient hybrid seed production by eliminating the need for emasculation. In squash (Cucurbita pepo L.), genetic male sterility is controlled by a single recessive gene designated ms-2. The phenotype conferred by ms-2 is characterized by shriveling and browning of the androecium. Marker-assisted selection targeting ms-2 would allow rapid introgression into elite squash inbred lines, but its genomic location is currently unknown. In the current study, an F2 bi-parental mapping population segregating male sterility was phenotyped in the greenhouse and subsequently used to identify genomic regions linked to the trait. QTL detection was performed using a combination of traditional linkage mapping and QTL-seq based on whole-genome resequencing. Using traditional linkage mapping, a major QTL explaining > 50% of the phenotypic variation was observed on LG4 of the squash genome. The QTL-seq strategy confirmed the loci on LG4, but additionally detected five other QTLs across the genome. A candidate gene encoding a ‘Novel INteractor of JAz’ (NINJA) protein was identified within the QTL on LG4. Cloning and sequence analysis of this gene identified sequence variants that could be useful for marker-assisted selection in squash.