Powdery mildew (PM) is the main disease that afflicts bottle gourd. Previous studies on PM mainly focused on its effects on pumpkin, melon, and other crops; however, the exact molecular mechanism of bottle gourd resistance to PM remains unclear. RNA sequencing (RNA-Seq) technology was used to investigate the dynamic changes in leaf transcriptome profiles between resistant and susceptible gourd at 12, 24, 48, and 72 h post-inoculation with powdery mildew. Compared with a susceptible variety (G3), the expression levels of the differentially expressed genes of phenylpropanoid biosynthesis, starch, and sucrose metabolism, and plant–pathogen interaction pathways in disease-resistant plants were upregulated. We propose that disease resistance and tolerance in bottle gourd are enhanced via several pathways, including the antioxidant system, phenylalanine biosynthesis, and cell wall cellulose synthesis. Our research will provide an important basis for further screening and breeding PM resistance in bottle gourd.

Powdery mildew is one of the most destructive fungal diseases of bottle gourd (Lagenaria siceraria), severely threatening yield and quality, yet the genetic basis of its resistance remains poorly understood. In this study, an F₂ segregating population derived from a cross between the resistant inbred line G6 and the susceptible inbred line G3 was used, and BSA-seq, integrated RNA-seq analysis, qRT-PCR validation, and KASP marker development were comprehensively employed. SNP-index and InDel-index analyses independently mapped and converged on a candidate interval of 1,898,234–8,241,294 bp (~6.34 Mb) on chromosome 2. By comparing differentially expressed genes (DEGs) at 12, 24, 48, and 72 h post-inoculation with the BSA candidate interval, one candidate resistance gene, Lsi02G006660, was identified, and a KASP marker (Chr2_5941698, G/T) was successfully developed. This study provides a candidate gene and marker resources for molecular breeding of powdery mildew resistance in bottle gourd.