Gummy Stem Blight Resistance in Melon: Inheritance Pattern and Development of Molecular Markers

et al. 2020

Preprint

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Background Bacterial fruit blotch (BFB), a disease caused by Acidovorax citrulli , results in significant economic losses in melon. The causal QTLs and genes for resistance to this disease have yet to be identified. Resistance ( R )-genes play vital roles in resistance to plant diseases. Since the complete genome sequence of melon is available and genome-wide identification of R -genes has been performed for this important crop, comprehensive expression profiling may lead to the identification of putative candidate genes that function in the response to BFB. Results We identified melon accessions that are resistant and susceptible to BFB through repeated bioassays and characterized all 70 R -genes in melon, including their gene structures, chromosomal locations, domain organizations, motif distributions, and syntenic relationships. Several disease resistance-related domains were identified, including NBS, TIR, LRR, CC, RLK, and DUF domains, and the genes were categorized based on the domains of their encoded proteins. In addition, we profiled the expression patterns of the genes in melon accessions with contrasting levels of BFB resistance at 12 h, 1 d, 3 d, and 6 d after inoculation with A. citrulli via qRT-PCR. Six R -genes exhibited consistent expression patterns (MELO3C023441, MELO3C016529, MELO3C022157, MELO3C022146, MELO3C025518, and MELO3C004303), with higher expression levels in the resistant vs. susceptible accession. Conclusion We identified six putative candidate R -genes against BFB in melon. Upon functional validation, these genes could be targeted for manipulation via breeding and biotechnological approaches to improve BFB resistance in melon in the future.

Section: Discussionsupporting

confidence: 78%

Section: Discussionmentioning

confidence: 56%

Characterization, Identification and Expression Profiling of Genome-Wide R-Genes in Melon and Their Putative Roles in Bacterial Fruit Blotch Resistance

et al. 2020

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“…In watermelon, six NBS-encoding R-genes were identi ed as candidates for gummy stem blight (GSB) resistance [81,82]. Finally, markers have been developed for detecting both GSB and BFB resistance in melon based on the sequence polymorphism in the TIR-NBS-LRR gene MELO3C022157 [81,83]. Notably, all six candidate R-genes identi ed in the current study have corresponding homologues in watermelon and cucumber (Fig.…”

Section: Discussionmentioning

confidence: 83%

“…In addition, a study of the MLO (mildew resistance locus o) gene family in melon revealed candidate genes that might play roles in susceptibility to powdery mildew [80]. In watermelon, six NBS-encoding R-genes were identi ed as candidates for gummy stem blight (GSB) resistance [81,82]. Finally, markers have been developed for detecting both GSB and BFB resistance in melon based on the sequence polymorphism in the TIR-NBS-LRR gene MELO3C022157 [81,83].…”

Section: Discussionmentioning

confidence: 99%

Characterization, Identification and Expression Profiling of Genome-Wide R-Genes in Melon and Their Putative Roles in Bacterial Fruit Blotch Resistance

et al. 2020

Preprint

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Abstract Background: Bacterial fruit blotch (BFB), a disease caused by Acidovorax citrulli, results in significant economic losses in melon. The causal QTLs and genes for resistance to this disease have yet to be identified. Resistance (R)-genes play vital roles in resistance to plant diseases. Since the complete genome sequence of melon is available and genome-wide identification of R-genes has been performed for this important crop, comprehensive expression profiling may lead to the identification of putative candidate genes that function in the response to BFB.Results: We identified melon accessions that are resistant and susceptible to BFB through repeated bioassays and characterized all 70 R-genes in melon, including their gene structures, chromosomal locations, domain organizations, motif distributions, and syntenic relationships. Several disease resistance-related domains were identified, including NBS, TIR, LRR, CC, RLK, and DUF domains, and the genes were categorized based on the domains of their encoded proteins. In addition, we profiled the expression patterns of the genes in melon accessions with contrasting levels of BFB resistance at 12 h, 1 d, 3 d, and 6 d after inoculation with A. citrulli. Six R-genes exhibited consistent expression patterns (MELO3C023441, MELO3C016529, MELO3C022157, MELO3C022146, MELO3C025518, and MELO3C004303), with higher expression levels in the resistant vs. susceptible accession. Conclusion: We identified six putative candidate R-genes against BFB in melon. Upon functional validation, these genes could be targeted for manipulation via breeding and biotechnological approaches to improve BFB resistance in melon in the future.

“…The disease severity of three individual leaves from each inoculated plant was scored 12 days after inoculation using a scale of 1 to 6 (Supplementary Figure S1) for ≥10%, 11-20%, 21-50%, 51-75%, 76-90% and >90% diseased/infected area per leaf, respectively [18]. Disease ratings were scored as per the methods described by Robin et al [36] and Hassan et al [37] with little modification. The percentage infected area (PIA) was measured as the ratio of infected area to total leaf area, multiplied by 100.…”

Section: Inoculation Sample Preparation and Assessment Of Bfb Resistmentioning

confidence: 99%

Development of Molecular Marker Linked with Bacterial Fruit Blotch Resistance in Melon (Cucumis melo L.)

et al. 2020

Genes

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Bacterial fruit blotch (BFB) causes losses in melon marketable yield. However, until now, there has been no information about the genetic loci responsible for resistance to the disease or their pattern of inheritance. We determined the inheritance pattern of BFB resistance from a segregating population of 491 F2 individuals raised by crossing BFB-resistant (PI 353814) and susceptible (PI 614596) parental accessions. All F1 plants were resistant to Acidovorax citrulli strain KACC18782, and F2 plants segregated with a 3:1 ratio for resistant and susceptible phenotypes, respectively, in a seedling bioassay experiment, indicating that BFB resistance is controlled by a monogenic dominant gene. In an investigation of 57 putative disease-resistance related genes across the melon genome, only the MELO3C022157 gene (encoding TIR-NBS-LRR domain), showing polymorphism between resistant and susceptible parents, revealed as a good candidate for further investigation. Cloning, sequencing and quantitative RT-PCR expression of the polymorphic gene MELO3C022157 located on chromosome 9 revealed multiple insertion/deletions (InDels) and single nucleotide polymorphisms (SNPs), of which the SNP A2035T in the second exon of the gene caused loss of the LRR domain and truncated protein in the susceptible accession. The InDel marker MB157-2, based on the large (504 bp) insertion in the first intron of the susceptible accession, was able to distinguish resistant and susceptible accessions among 491 F2 and 22 landraces/inbred accessions with 98.17% and 100% detection accuracy, respectively. This novel PCR-based, co-dominant InDel marker represents a practical tool for marker-assisted breeding aimed at developing BFB-resistant melon accessions.