Mosaic (HBC 369): A New Flavor Hop Variety

The aim of the study was to evaluate the possible role of endophytic fungi (EF) on Rosa powdery mildew (PM) resistance. The endophytic fungal communities of two wild Rosa varieties with different PM susceptibilities were investigated through both culture-dependent and independent methods, and the antagonistic activities of endophytes against the PM pathogen were evaluated by pot experiments. There were more OTUs recovered from the PM resistant variety than from the PM susceptible variety. Similarly, the culturable EF from the PM resistant variety (1333 isolates) was more than that from the PM susceptible variety (670 isolates). Consistent with this, the colonization rate of culturable EF of the PM resistant variety was significantly higher than that of the PM susceptible variety at each PM stage (p < 0.05). In addition, it was found that the dominant EF of both varieties were different using culture-dependent and independent methods. The α-diversity of both culturable and un-culturable EF were similar except at the early stage of PM infection. Pot experiments showed that the strain M7SB 41 (Seimatosporium sp.) from PM resistant variety significantly enhanced host plant PM resistance. The results suggested that the endophytic fungal communities of two wild Rosa varieties with different PM susceptibilities were significantly different, and the PM resistant Rosa variety harbored more EF than susceptible Rosa variety, and some EF played an important role in host plant PM resistance.

A limited genetic mapping strategy based on simple sequence repeat (SSR) marker data was used with five grape populations segregating for powdery mildew (Erysiphe necator) resistance in an effort to develop genetic markers from multiple sources and enable the pyramiding of resistance loci. Three populations derived their resistance from Muscadinia rotundifolia ‘Magnolia’. The first population (06708) had 97 progeny and was screened with 137 SSR markers from seven chromosomes (4, 7, 9, 12, 13, 15, and 18) that have been reported to be associated with powdery or downy mildew resistance. A genetic map was constructed using the pseudo-testcross strategy and QTL analysis was carried out. Only markers from chromosome 13 and 18 were mapped in the second (04327) and third (06712) populations, which had 47 and 80 progeny, respectively. Significant QTLs for powdery mildew resistance with overlapping genomic regions were identified for different tissue types (leaf, stem, rachis, and berry) on chromosome 18, which distinguishes the resistance in ‘Magnolia’ from that present in other accessions of M. rotundifolia and controlled by the Run1 gene on chromosome 12. The ‘Magnolia’ resistance locus was termed as Run2.1. Powdery mildew resistance was also mapped in a fourth population (08391), which had 255 progeny and resistance from M. rotundifolia ‘Trayshed’. A locus accounting for 50% of the phenotypic variation mapped to chromosome 18 and was named Run2.2. This locus overlapped the region found in the ‘Magnolia’-based populations, but the allele sizes of the flanking markers were different. ‘Trayshed’ and ‘Magnolia’ shared at least one allele for 68% of the tested markers, but alleles of the other 32% of the markers were not shared indicating that the two M. rotundifolia selections were very different. The last population, 08306 with 42 progeny, derived its resistance from a selection Vitis romanetii C166-043. Genetic mapping discovered a major powdery mildew resistance locus termed Ren4 on chromosome 18, which explained 70% of the phenotypic variation in the same region of chromosome 18 found in the two M. rotundifolia resistant accessions. The mapping results indicate that powdery mildew resistance genes from different backgrounds reside on chromosome 18, and that genetic markers can be used as a powerful tool to pyramid these loci and other powdery mildew resistance loci into a single line.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-010-1511-6) contains supplementary material, which is available to authorized users.

To identify the powdery mildew (PM) resistance gene in mungbean, inter-simple sequence repeat (ISSR) markers and newly developed ISSR-anchored resistance gene analog (ISSR-RGA) markers were evaluated. When F2:7 and F2:8 recombinant inbred line populations derived from a cross between CN72 (susceptible cultivar in Thailand) and V4718 (resistant line from Asian Vegetable Research and Development Center) were evaluated for PM resistance under field conditions, the PM resistance gene from V4718 was found to be inherited as a single major gene. Fifteen out of 75 ISSR primers produced 27 DNA bands putatively associated with PM resistance in bulk segregant analysis (BSA). Ten ISSR primers were combined with four RGA primers homologous to the nucleotide-binding site and kinase domains of resistance (R) genes to generate 40 ISSR-RGA primer combinations. When these 40 ISSR-RGA primer combinations and 10 corresponding ISSR primers were used in BSA, 873 ISSR and 756 ISSR-RGA loci were amplified. Fifty-two of 756 ISSR-RGA loci were new, and 11 of these 23 ISSR-RGA loci were putatively associated with the PM resistance. Simple linear regression confirmed that 5 of the 27 ISSR markers and 3 of the 11 ISSR-RGA markers were significantly associated with the PM resistance gene. When these eight ISSR and ISSR-RGA markers were used for quantitative trait loci (QTL) analysis, multiple interval mapping identified a major QTL, qPMC72V18-1, explaining up to 92.4% of the phenotypic variation, flanked by I42PL229 and I85420 markers at the distance of 4 and 9 cM, respectively. These results suggest that ISSR and ISSR-RGA markers are highly efficient tools for mapping PM resistance gene in mungbean. The markers closely linked to the PM resistance gene will be useful for future marker-assisted selection to develop mungbean varieties resistant to PM.

Key message A single recessive gene for complete resistance to powdery mildew and a major-effect QTL for partial resistance to downy mildew were co-localized in a Cucumis hystrix introgression line of cucumber. Downy mildew (DM) and powdery mildew (PM) are two major foliar diseases in cucumber. DM resistance (DMR) and PM resistance (PMR) may share common components; however, the genetic relationship between them remains unclear. IL52, a Cucumis hystrix introgression line of cucumber which has been reported to possess DMR, was recently identified to exhibit PMR as well. In this study, a single recessive gene pm for PMR was mapped to an approximately 468-kb region on chromosome 5 with 155 recombinant inbred lines (RILs) and 193 F2 plants derived from the cross between a susceptible line 'changchunmici' and IL52. Interestingly, pm was co-localized with the major-effect DMR QTL dm5.2 confirmed by combining linkage analysis and BSA-seq, which was consistent with the observed linkage of DMR and PMR in IL52. Further, phenotype-genotype correlation analysis of DMR and PMR in the RILs indicated that the co-localized locus pm/dm5.2 confers complete resistance to PM and partial resistance to DM. Seven candidate genes for DMR were identified within dm5.2 by BSA-seq analysis, of which Csa5M622800.1, Csa5M622830.1 and Csa5M623490.1 were also the same candidate genes for PMR. A single nucleotide polymorphism that is present in the 3' untranslated region (3'UTR) of Csa5M622830.1 co-segregated perfectly with PMR. The GATA transcriptional factor gene Csa5M622830.1 may be a likely candidate gene for DMR and PMR. This study has provided a clear evidence for the relationship between DMR and PMR in IL52 and sheds new light on the potential value of IL52 for cucumber DMR and PMR breeding program.

Powdery mildew resistance in zucchini is controlled by one major dominant locus, CpPM10.1. CpPM10.1 was fine mapped. The expression of candidate gene Cp4.1LG10g02780 in resistant individuals was significantly upregulated after inoculation with the powdery mildew. Powdery mildew (PM) is one of the most destructive fungal diseases, reducing the productivity of Cucurbita crops globally. PM influences the photosynthesis, growth and development of infected zucchini and seriously reduces fruit yield and quality. In the present study, the zucchini inbred line 'X10' had highly stable PM resistance, and the inbred line 'Jin234' was highly susceptible to PM in the seedling stage and adult stages. Genetic analysis revealed that PM resistance in 'X10' is controlled by one major dominant locus. Based on the strategy of QTL-seq combined with linkage analysis and developed molecular markers, the major locus was found to be located in a 382.9-kb candidate region on chromosome 10; therefore, the major locus was named CpPM10.1. Using 1,400 F2 individuals derived from a cross between 'X10' and 'JIN234' and F2:3 offspring of the recombinants, the CpPM10.1 locus was defined in a region of approximately 20.9kb that contained 5 coding genes. Among them, Cp4.1LG10g02780 contained a conserved domain (RPW8), which controls resistance to a broad range of PM pathogens. Cp4.1LG10g02780 also had nonsynonymous SNPs between the resistant 'X10' and susceptible 'Jin234.' Furthermore, the expression of Cp4.1LG10g02780 was strongly positively involved in PM resistance in the key period of inoculation. Further allelic diversity analysis in zucchini germplasm resources indicated that PM resistance was associated with two SNPs in the Cp4.1LG10g02780 RPW8 domain. This study not only provides highly stable PM resistance gene resources for cucurbit crops but also lays the foundation for the functional analysis of PM resistance and resistance breeding in zucchini.

Candidate gene mapping reveals VrMLO12 (MLO Clade II) is associated with powdery mildew resistance in mungbean (Vigna radiata [L.] Wilczek)

Gene pyramiding is an effective strategy to provide a durable and high level of powdery mildew (PM) resistance in mungbean [Vigna radiata (L.) R. Wilczek]. The objectives of this study were to evaluate PM resistance levels of pyramided BC2F1 progenies derived from marker-assisted selection of KING (recurrent parent) × SUPER5 (donor parent) cross and measure their agronomic performance under fi eld condition. The results showed that the progenies with marker combinations linked to both PM resistance genes including I85420 + I42PL222, and I27R565 were more resistant to PM (average disease severity score of 3.80) than KING, check cv. CN72, and the progenies without any marker combinations (scores of 8, 8 and 6.75, respectively). While the progenies carrying only one resistance gene were identifi ed as containing either I85420 + I42PL222, or I27R565 which showed intermediate response score of 5.83. In addition, most of the pyramided lines produced higher yield per plant than KING because of their superior pods per plant, clusters per plant, and seeds per pod. In the future, these pyramided lines with two PM resistance genes can be further developed into new PM resistant varieties via marker-assisted backcross breeding or be used as potential PM resistant sources in mungbean breeding programs.

Broad-spectrum disease resistance is a highly valuable trait in plant breeding and attracts special attention in research. The Arabidopsis gene locus RESISTANCE TO POWDERY MILDEW 8 (RPW8) contains two adjacent homologous genes, RPW8.1 and RPW8.2, and confers broad-spectrum resistance to powdery mildew. Remarkably, the RPW8.2 protein is specifically localized to the extrahaustorial membrane (EHM) encasing the feeding structure of powdery mildew whereby RPW8.2 activates haustorium-targeted defenses. Here, we show that ectopic expression of the yellow fluorescent protein (YFP)-tagged RPW8.1 from the native promoter leads to unique cell death lesions and enhances resistance to virulent fungal and oomycete pathogens that cause powdery mildew and downy mildew diseases, respectively. In powdery mildew-infected plants, RPW8.1-YFP accumulates at higher levels in the mesophyll cells underneath the infected epidermal cells where RPW8.2-YFP is mainly expressed. This cell type-preferential protein accumulation pattern largely correlates with that of H(2)O(2) accumulation, suggesting that RPW8.1 may spatially collaborate with RPW8.2 in activation of resistance to powdery mildew. Interestingly, when ectopically expressed from the RPW8.2 promoter, RPW8.1-YFP is also targeted to the EHM of powdery mildew and the transgenic plants display resistance to both powdery mildew and downy mildew. Using YFP as a reporter, we further reveal that the RPW8.1 promoter is constitutively active but induced to higher levels in cells at the infection site, whereas the RPW8.2 promoter is activated specifically in cells at the infection site. Taken together, our results suggest that RPW8.1 (and its promoter) is functionally distinct from RPW8.2 and may have a higher potential in engineering broad-spectrum resistance in plants.

Two genes for resistance to Podosphaera xanthii race 1 in melon were identified on chromosomes 10 and 12 of the Cucumis melo cultivar MR-1. Cucumis melo L. is an economically important crop, the production of which is threatened by the prevalence of melon powdery mildew (PM) infections. We herein utilized the MR-1 (P1; resistant to PM) and M4-7 (P2; susceptible to PM) accessions to assess the heritability of PM (race 1) resistance in these melon plants. PM resistance in MR-1 leaves was linked to a dominant gene (CmPMRl), whereas stem resistance was under the control of a recessive gene (CmPMrs), with the dominant gene having an epistatic effect on the recessive gene. The CmPMRl gene was mapped to a 50Kb interval on chromosome 12, while CmPMrs was mapped to an 89Kb interval on chromosome 10. The CmPMRl candidate gene MELO3C002441 and the CmPMrs candidate gene MELO3C012438 were identified through sequence alignment, functional annotation, and expression pattern analyzes of all genes within these respective intervals. MELO3C002441 and MELO3C012438 were both localized to the cellular membrane and were contained conserved NPR gene-like and MLO domains, respectively, which were linked to PM resistance. In summary, we identified patterns of PM resistance in the disease-resistant MR-1 melon cultivar and identified two putative genes linked to resistance. Our results offer new genetic resources and markers to guide future marker-assisted breeding for PM resistance in melon.

Powdery mildew (PM) is one of the most serious diseases in cucumber and causes huge yield loss. Multiple quantitative trait loci (QTLs) for PM resistance have been reported in previous studies using a limited number of cucumber accessions. In this study, a cucumber core germplasm (CG) consisting of 94 resequenced lines was evaluated for PM resistance in four trials across three years (2013, 2014, and 2016). These trials were performed on adult plants in the field with natural infection. Using genome-wide association study (GWAS), 13 loci (pmG1.1, pmG1.2, pmG2.1, pmG2.2, pmG3.1, pmG4.1, pmG4.2, pmG5.1, pmG5.2, pmG5.3, pmG5.4, pmG6.1, and pmG6.2) associated with PM resistance were detected on all chromosomes except for Chr.7. Among these loci, ten were mapped to chromosomal intervals where QTLs had been reported in previous studies, while, three (pmG2.1, pmG3.1, and pmG4.1) were novel. The loci of pmG2.1, pmG5.2, pmG5.3 showed stronger signal in four trials. Based on the annotation of homologous genes in Arabidopsis and pairwise LD correlation analysis, candidate genes located in the QTL intervals were predicted. SNPs in these candidate genes were analyzed between haplotypes of highly resistant (HR) and susceptible (HS) CG lines, which were defined based on combing disease index data of all trials. Furthermore, candidate genes (Csa5G622830 and CsGy5G015660) reported in previous studies for PM resistance and cucumber orthologues of several PM susceptibility (S) genes (PMR5, PMR-6, and MLO) that are colocalized with certain QTLs, were analyzed for their potential contribution to the QTL effect on both PM and DM in the CG population. This study shows that the CG germplasm is a very valuable resource carrying known and novel QTLs for both PM and DM resistance, which can be exploited in cucumber breeding.

The Mildew Resistance Locus (Mlo) gene family is reported in various species as regulators of powdery mildew (PM) resistance. However, the Mlo genes in cucurbit crops remain limited. In this study, a genome-wide investigation of Mlo genes was conducted in eight Cucurbitaceae species and in rice, maize, arabidopsis, and barley, and a total of 202 Mlo genes were identified. The phylogenetic analysis showed that 202 Mlo genes can be classified into six clades, and the Mlo genes from clades I and III are likely pivotal in regulating PM resistance in dicotyledonous and monocotyledonous plants, respectively. The Ka/Ks ratios for these homologous Mlo gene pairs ranged from 0 to 0.6, revealing that they underwent substantial purifying selection during evolution. Among 12 crops, there were the most Mlo genes (22 Cm-mlo) in melon. An expression analysis revealed that six Cm-mlo genes showed expression responses to PM infection in which Cm-mlo38 and Cm-mlo44 were phylogenetically close to Mlo genes that regulated PM resistance. Using the VIGS system for silencing, Cm-mlo38 and Cm-mlo44 enhanced resistance to PM in susceptible material. A protein interaction analysis indicated that Cm-mlo38 might regulate PM resistance through interactions with PR5 and CML proteins. These results provide a comprehensive understanding of the Mlo family in Cucurbitaceae and pave the way for future functional analysis and genetic improvement for improving PM resistance in Cucurbitaceae.

Field grown seedlings potentially carrying both the Run1 and Rpv1 loci for powdery and downy mildew resistance, respectively, from muscadine (Vitis rotundifolia) introgressions were assessed for resistance to both powdery and downy mildew. Powdery mildew was assessed in the field under no-spray conditions, while downy mildew was assessed using a detached leaf assay in vitro. In these populations, markers for the Run1 gene were excellent predictors of powdery mildew resistance, but markers for the Rpv1 gene were not useful in predicting downy mildew resistance. Markers for Ren2 powdery mildew resistance derived from Vitis cinerea were also useful. Populations that were previously selected for powdery mildew resistance (where the susceptible types had already been discarded) had a very high frequency of markers for the Run1 gene and/or the V. cinerea source of resistance, confirming the success of field screening techniques. By screening for the presence of markers, it was possible to identify seedlings harboring both the V. cinerea as well as muscadine sources of powdery mildew resistance.

Genome-wide characterization and expression analysis of the MLO gene family sheds light on powdery mildew resistance in Lagenaria siceraria

Host resistances in PI 197088 cucumber to downy and powdery mildew pathogens are conferred by 11 (3 with major effect) and 4 (1 major effect) QTL, respectively, and three of which are co-localized. The downy mildew (DM) and powdery mildew (PM) are the two most important foliar diseases of cucurbit crops worldwide. The cucumber accession PI 197088 exhibits high-level resistances to both pathogens. Here, we reported QTL mapping results for DM and PM resistances with 148 recombinant inbred lines from a cross between PI 197088 and the susceptible line 'Coolgreen'. Phenotypic data on responses to natural DM and PM infection were collected in multi-year and multi-location replicated field trials. A high-density genetic map with 2780 single nucleotide polymorphisms (SNPs) from genotyping-by-sequencing and 55 microsatellite markers was developed, which revealed genomic regions with segregation distortion and mis-assemblies in the '9930' cucumber draft genome. QTL analysis identified 11 and 4 QTL for DM and PM resistances accounting for more than 73.5 and 63.0% total phenotypic variance, respectively. Among the 11 DM resistance QTL, dm5.1, dm5.2, and dm5.3 were major-effect contributing QTL, whereas dm1.1, dm2.1, and dm6.2 conferred susceptibility. Of the 4 QTL for PM resistance, pm5.1 was the major-effect QTL explaining 32.4% phenotypic variance and the minor-effect QTL pm6.1 contributed to disease susceptibility. Three PM QTL, pm2.1, pm5.1, and pm6.1, were co-localized with DM QTL dm2.1, dm5.2, and dm6.1, respectively, which was consistent with the observed linkage of PM and DM resistances in PI 197088. The genetic architecture of DM resistance in PI 197088 and another resistant line WI7120 (PI 330628) was compared, and the potential of using PI 197088 in cucumber breeding for downy and powdery mildew resistances is discussed.

Two genes, CsLRR-RPK2 (CsGy5G015660) and CsaMLO8 (Csa5G623470), have been considered as powdery mildew (PM) resistance genes in cucumbers. In this study, we evaluated the involvement of the alleles of these two genes in PM resistance in 100 commercial Korean cucumber inbred lines. To achieve this, we developed cleaved amplified polymorphic sequences (CAPS) and InDel markers from CsLRR-RPK2 and CsaMLO8. Genotyping analysis indicated that the CsLRR-RPK2-CAPS marker showed a stronger correlation with the PM-resistant phenotype, with an 84% consistency compared to the CsaMLO8-InDel marker. The use of the CsaMLO8-InDel marker showed a 70% consistency between phenotype and genotype results. It was proposed that the CsLRR-RPK2-CAPS marker successfully eliminated PM-susceptible inbred lines, since both genotype and phenotype results were 100% identical. Furthermore, the present study revealed that the introduction of one of these alleles is probably enough to confer PM resistance in cucumbers. However, seven PM-resistant inbred lines harbored either CsaMLO8 or CsLRR-RPK2 alleles, indicating that there is another PM-resistant resource(s) besides CsaMLO8- and CsLRR-RPK2–originated resistance in the commercial Korean inbred lines. Our results provide reliable evidence confirming two PM-resistant candidate genes for the detection of PM resistance resources in cucumber inbred lines.