Abstract
Gummy stem blight (GSB) causes enormous losses to melon (Cucumis melo L.) production worldwide. We aimed to develop useful molecular markers linked to GSB resistance. In this study, 168 F2 plants were obtained from the F1 population of a cross between the GSB-susceptible ‘Cornell ZPPM 339’ and the GSB-resistant ‘PI482399’ lines. A 3:1 ratio of susceptible and resistant genotypes was observed in the F2 population, indicating control by a single recessive gene. Nucleotide-binding site leucine-rich repeat (NBS-LRR) genes confer resistance against insects and diseases in cucurbits including melon. We cloned and sequenced the TIR-NBS-LRR-type resistance gene MELO3C022157, located on melon chromosome 9, from resistant and susceptible lines. Sequence analysis revealed deletions in the first intron, a 2-bp frameshift deletion from the second exon and a 7-bp insertion in the 4th exon of the resistant line. We developed two insertion/deletion (InDel) markers, GSB9-kh-1 and GSB9-kh-2, which were found in the first intron of MELO3C022157 linked to GSB resistance. We validated these markers with the F2 population and inbred lines. These InDels may be used to facilitate marker-assisted selection of GSB resistance in melon. However, functional analysis of overexpressing and/or knock-down mutants is needed to confirm the frameshift mutation.
Highlights
Cultivated melon (Cucumis melo L.) is an economically important member of the Cucurbitaceae family, which includes a diverse group of annual trailing vine plants, such as honeydew, cantaloupe, mango melon, snake melon, snap melon, and pickling melon [1]
The inheritance pattern of Gummy stem blight (GSB) resistance was analyzed in the F2 population of melon
A Chi-square test showed that GSB resistance segregated in a ratio of 3:1, which is consistent with a monogenic recessive trait (Table 1 and Figure S1)
Summary
Cultivated melon (Cucumis melo L.) is an economically important member of the Cucurbitaceae family, which includes a diverse group of annual trailing vine plants, such as honeydew, cantaloupe, mango melon, snake melon, snap melon, and pickling melon [1]. Gummy stem blight (GSB), which is caused by the fungal pathogen Didymella bryoniae (Auersw.) Rehm, is a devastating disease of cucurbitaceous crops, including melon, throughout the world [4,5]. Symptoms of the disease include yellowing of the leaf margins (chlorosis), while at later stages, this yellowing spreads to form light to dark brown spots (necrosis) across the entire leaf surface. This results in stem canker of the cortical tissue that produces a characteristic brown, gummy exudate that is caused by water soaking of the leaves and hypocotyls. In a susceptible interaction, these lesions linger and expand, girdling the stem and leading to wilting and plant death [6]
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