Abstract
Watermelon (Citrullus lanatus) is a nutritionally rich and economically important horticultural crop of the Cucurbitaceae family. Gummy stem blight (GSB) is a major disease of watermelon, which is caused by the fungus Didymella bryoniae, and results in substantial economic losses in terms of yield and quality. However, only a few molecular studies have focused on GSB resistance in watermelon. Nucleotide binding site (NBS)-encoding resistance (R) genes play important roles in plant defense responses to several pathogens, but little is known about the role of NBS-encoding genes in disease resistance in watermelon. The analyzed NBS-encoding R genes comprises several domains, including Toll/interleukin-1 receptor(TIR), NBS, leucine-rich repeat (LRR), resistance to powdery mildew8(RPW8) and coiled coil (CC), which are known to be involved in disease resistance. We determined the expression patterns of these R genes in resistant and susceptible watermelon lines at different time points after D. bryoniae infection by quantitative RT-PCR. The R genes exhibited various expression patterns in the resistant watermelon compared to the susceptible watermelon. Only six R genes exhibited consistent expression patterns (Cla001821, Cla019863, Cla020705, Cla012430, Cla012433 and Cla012439), which were higher in the resistant line compared to the susceptible line. Our study provides fundamental insights into the NBS-LRR gene family in watermelon in response to D. bryoniae infection. Further functional studies of these six candidate resistance genes should help to advance breeding programs aimed at improving disease resistance in watermelons.
Highlights
Watermelon (Citrullus lanatus) is one of the most important cucurbit crops worldwide
We found that the genes are differentially expressed in susceptible compared to resistant C. lanatus lines
The greatest number of motifs was identified in the coiled coil (CC)-Nucleotide binding site (NBS)-leucine-rich repeat (LRR) domain-containing gene Cla021858, whereas the fewest were detected in Cla001168 and Cla021846
Summary
Watermelon (Citrullus lanatus) is one of the most important cucurbit crops worldwide. Due to the agricultural importance of this disease, early studies have focused on identifying the sources of genetic resistance to GSB [10] Few such sources have been reported in watermelon [4,7]. Resistance (R) genes play important roles in plant immune systems in response to various pathogens and insects, including viruses, bacteria, fungi, aphids and nematodes [11]. Since NBS-encoding R genes have been reported to confer resistance against various pathogens and insects in different plant species, the R genes were explored in watermelon. In this study, we analyzed the expression patterns of NBS-encoding genes in D. bryoniae-resistant and -susceptible watermelon lines to identify candidate R genes conferring resistance to GSB, which could be highly useful for breeding programs
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