Disease Of Cucumber Research Articles

Probability Maximum Margin Criterion for Crop Disease Recognition

<abstract> <sc><b>Abstract.</b> </sc>Crop disease seriously affects the yield and quality of crops and cause farmers to experience economic losses. Automatic detection of crop disease is an essential research topic to detect the disease symptoms as soon as they appear on the leaves. For crop disease management, it is important to automatically detect the crop diseases at a stage so as to treat them properly. In subspace dimension reduction-based data classification methods, the main topic is to design the between-class and within-class scatter matrices to obtain the mapping matrix from the training samples. But, there is much difference between the training samples. To eliminate the difference in designing the scatter matrices, in this article, based on the prior probability, a probability maximum margin criterion (MMC) is proposed for leaf spot image processing. Compared to the traditional MMC algorithm, in the proposed method, the two scatter matrices are expressed by the weighted mean vector of all training samples, which can overcome the influence of the outliers and the noise points, meanwhile improve the crop disease recognition rate. In this study, more than 100 classifying features are extracted from the disease leaf images of two kinds of cucumber diseases; probability MMC is performed for reduced dimensions in feature data processing, and then K-nearest-neighbor classifier is used to identify the cucumber diseases. The experimental results on a cucumber disease leaf image database show that the proposed method is effective for crop disease recognition.

QTL mapping for downy mildew resistance in cucumber via bulked segregant analysis using next-generation sequencing and conventional methods.

QTL mapping using NGS-assisted BSA was successfully applied to an F 2 population for downy mildew resistance in cucumber. QTLs detected by NGS-assisted BSA were confirmed by conventional QTL analysis. Downy mildew (DM), caused by Pseudoperonospora cubensis, is one of the most destructive foliar diseases in cucumber. QTL mapping is a fundamental approach for understanding the genetic inheritance of DM resistance in cucumber. Recently, many studies have reported that a combination of bulked segregant analysis (BSA) and next-generation sequencing (NGS) can be a rapid and cost-effective way of mapping QTLs. In this study, we applied NGS-assisted BSA to QTL mapping of DM resistance in cucumber and confirmed the results by conventional QTL analysis. By sequencing two DNA pools each consisting of ten individuals showing high resistance and susceptibility to DM from a F2 population, we identified single nucleotide polymorphisms (SNPs) between the two pools. We employed a statistical method for QTL mapping based on these SNPs. Five QTLs, dm2.2, dm4.1, dm5.1, dm5.2, and dm6.1, were detected and dm2.2 showed the largest effect on DM resistance. Conventional QTL analysis using the F2 confirmed dm2.2 (R 2=10.8-24%) and dm5.2 (R 2=14-27.2%) as major QTLs and dm4.1 (R 2=8%) as two minor QTLs, but could not detect dm5.1 and dm6.1. A new QTL on chromosome 2, dm2.1 (R 2=28.2%) was detected by the conventional QTL method using an F3 population. This study demonstrated the effectiveness of NGS-assisted BSA for mapping QTLs conferring DM resistance in cucumber and revealed the unique genetic inheritance of DM resistance in this population through two distinct major QTLs on chromosome 2 that mainly harbor DM resistance.

Comparative proteomic analysis of cucumber roots infected by Fusarium oxysporum f. sp. cucumerium Owen

Cucumber Fusarium wilt (CFW), caused by the soil-borne fungus Fusarium oxysporum f. sp. cucumerium, is a serious disease in cucumber (Cucumis sativus) production worldwide. For the efficient control of the pathogenic fungi, a better understanding of its interaction and associated resistance mechanisms at the molecular level is required. Here, we report a comparative proteomics analysis of total root protein isolated from infected cucumber root of susceptible bulk (SB) and resistant bulk (RB) of cucumber generation F2. Two-dimensional gel electrophoresis (2-DE) coupled with MS/MS approaches identified 15 over-accumulated proteins from the RB plants. Identified proteins are mainly involved in defense and stress responses, oxidation reduction, metabolism and transport and other process. These proteins are likely to be a part of resistance-related protein network, playing different roles in cucumber disease resistance. Three vital clues regarding wilt resistance of C. sativus are gained from this study. First, jasmonic acid and redox signaling components were found in response to F. oxysporum infection in resistant plants. Second, the LRR family protein may play an important role in the defense reaction against CFW. Third, biotic and abiotic stress-related proteins were induced by the CFW fungus F. oxysporum, indicating the activation of common stress pathway.

Safe Method to Control Powdery Mildew Disease of Pepper and Cucumber

Safe Method to Control Powdery Mildew Disease of Pepper and Cucumber

Genetic analysis and fine mapping of Watermelon mosaic virus resistance gene in cucumber

Watermelon mosaic virus (WMV) is an important disease of cucumber (Cucumis sativus L.) that is difficult to control in the field. Some resistant lines are available, and understanding the inheritance of the disease and mapping the gene or genes that confer resistance will facilitate the development of further resistant varieties. In this study, the inheritance and gene mapping for resistance to WMV in cucumber were conducted using populations derived from the cross between susceptible ‘65G’ and resistant ‘02245’ inbred lines. Genetic analysis showed that resistance to WMV in ‘02245’ is controlled by a single recessive gene designated as wmv 02245 mapped to chromosome 6 (Chr.6). The region was flanked by the molecular markers SSRWMV60-23 and CAPS-W1 with genetic distances of 0.34 and 1.19 cM from the wmv 02245 locus, respectively. The 134.7 kb physical distance of this region includes 21 candidate genes. Comparison of the genotypic and phenotypic results showed that the accuracy rate of the most closely linked marker SSRWMV60-23 was 94.0 %. This marker will be used for molecular marker-assisted selection to select resistant lines, and future research will be directed at identifying and cloning the resistance gene.

Downy Mildew Disease Progress in Resistant and Susceptible Cucumbers Tested in the Field at Different Growth Stages

Downy mildew, caused by the oomycete pathogen Pseudoperonospora cubensis (Berkeley &amp; Curtis) Rostov, is a major foliar disease of cucumber. Ten years after the reemergence of P. cubensis, downy mildew continues to be a major threat to cucumber production in the United States. Cucumber accessions with high levels of resistance have been identified. Development of cultivars with high levels of resistance remains an important objective of cucumber breeding programs. We tested a set of cucumber cultigens, including highly resistant PI accessions and susceptible control lines, to observe the effect of plant age on resistance. Cultigens responded differently to disease across plant developmental stages. In general, older plants had more disease symptoms, even those classified as resistant, such as PI 197088. However, PI 330628 and PI 605996 held their resistance even at late developmental stages. It is possible that these lines were resistant at late stages due to other factors, such as their rapid, indeterminate growth, that allows them to outgrow the disease. However, although PI 197088 appears to have a rapid, indeterminate growth habit, it did not have more resistance at later stages of plant maturity. Regardless of the mechanism involved, plant breeders should use the genetic resistance in PI 330628 and PI 605996 over PI 197088.

The Efficacy of Eco-friendly Botanicals in the Management of Damping-off and Downy Mildew Diseases of Cucumber

The Efficacy of Eco-friendly Botanicals in the Management of Damping-off and Downy Mildew Diseases of Cucumber

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This study was aimed to isolate and identify the phytopathogenic fungus Fusarium oxysporum f. sp. cucumerinum (Foc) the causal agent of the Fusarium vascular wilt disease of cucumber in the middle and south of Iraq. The results of study indicated the presence of the pathogen with percentage of appearance 71.43% with frequency 46.43%. Molecular identification carried out using polymerase chain reaction technique indicated the presence 18 isolates of Foc pathogenic group I and 6 isolate of Foc pathogenic group II. Among these, the isolate Foc-b3 was most virulent under in vitro pathogenicity test on the cucumber seed and it exhibited 0% seed germination compared with control. An attempt of integrated management of F. oxysporum f. sp. cucumerinum under in vitro conditions was also carried out in present study and a significant inhibition were reported on the application of various bioagents such as Chaetomium cupreum (Cc), Trichoderma viride (Tv) and Bacillus pumilus (Bp) on the potato dextrose agar (PDA). Further, under greenhouse conditions, combined application (tetrainoculums) of Cc+Tv+Bp+ Salicylic acid (Sa) was significantly reduced the percentage of the disease incidence and severity up to 0% as compared with the control where it was reported 97.50%, 75.72% respectively. Effect of this combination was also reported on the dry weight of the plants and significant improvement (0.975 gm/plant) was reported as compared to control (0.098 gm/plant). Safaa N. Hussein

Trichoderma harzianum-induced resistance against Fusarium oxysporum involves regulation of nuclear DNA content, cell viability and cell cycle-related genes expression in cucumber roots

Fusarium wilt, one of the destructive diseases of cucumber can be effectively controlled by using biocontrol agents such as Trichoderma harzianum. However, the mechanisms controlling T. harzianum-induced enhanced resistance remain largely unknown in cucumber plants. Here we screened the potent T. harzianum isolate TH58 that could effectively control F. oxysporum (FO). Glasshouse efficacy trials also showed that TH58 decreased disease incidence by 69.7 %. FO induced ROS over accumulation, while TH58 inoculation suppressed ROS over accumulation and improved root cell viability under F. oxysporum infection. TH58 inoculation could reverse the FO-induced cell division block and regulate the proportional distribution of nuclear DNA content through inducing 2C fraction. Moreover, the expression levels of cell cycle-related genes such as CDKA, CDKB, CycA, CycB, CycD3;1 and CycD3;2 in TH58 - pre-inoculated seedlings were up-regulated compared with those infected with FO alone. Taken together, these results suggest that T. harzianum improved plant resistance against Fusarium wilt disease via alterations in nuclear DNA content and cell cycle-related genes expression that might maintain a lower ROS accumulation and higher root cell viability in cucumber seedlings.

Cucumber disease recognition based on Global-Local Singular value decomposition

Plant leaf based plant disease recognition is becoming an important research topic in the pattern recognition and image processing. Many conventional methods are not effective for plant disease recognition because of the complexity of the disease leaf images. Singular value decomposition (SVD) has shown its advantage over other classical algorithms in terms of clustering accuracy and robustness to the data representation and feature extraction. Nonetheless, there is still considerable room to improve the practical application performance of SVD. To improve the recognition rate of cucumber disease, based on the Gglobal-Local SVD, a recognition method of cucumber disease is proposed. First, the spot image is segmented by the watershed algorithm from each cucumber disease leaf image. Second, each spot image is divided into a few blocks, and then the combining features of Global-Local singular values are extracted and ordered from each block by SVD. Third, the key-point vectors are constructed and their dimensionalities are adjusted to equal to each other. Finally, a SVM classifier is adopted to recognize the class of the unknown disease leaf image. Comparing with the existing cucumber disease recognition methods, the proposed one can extract the key-point features from the spot image whose dimension is significantly lower than that of the original space. Also, it can effectively avoid the key information loss in the usual stochastic feature extraction and selection process. The approach is tested on three kinds of cucumber disease leaf images. In the experiments, the original singular values are replaced by the nonnegative Global-Local Logarithmic singular values. The experimental results show that the proposed method is effective and feasible for the cucumber disease recognition, and has the highest recognition rate and more practical value.

Use of phages to control Vibrio splendidus infection in the juvenile sea cucumber Apostichopus japonicus.

In the present study, we isolated 3 bacteriophages with the ability to control Vibrio splendidus, a bacterium known to cause disease in the juvenile sea cucumber. These bacteriophages were designated as vB_VspS_VS-ABTNL-1 (PVS-1), vB_VspS_VS-ABTNL-2 (PVS-2) and vB_VspS_VS-ABTNL-3 (PVS-3). The ability of the 3 phages to inhibit the growth of V.splendidus VS-ABTNL was tested invitro using each of the 3 phages individually or in the form of a cocktail of all 3 phages in the proportion of 1:1:1. All treated cultures produced a significant (P<0.05) inhibition of growth of V.splendidus VS-ABTNL compared with untreated V.splendidus VS-ABTNL with the cocktail being superior to any of the 3 phages used individually. The lytic capability of the 3 phages was subsequently determined with a Spot Assay Technique performed with 4 isolates of V.splendidus, 3 other Vibrio species and 2 environmental isolates. Both PVS-1 and PVS-2 were lytic to all 4 isolates of V.splendidus while PVS-3 only inhibited the growth of 3 of them. V.splendidus VS-ABTNL was more susceptible to phage PVS-2 than the other 2 phages. In an invivo performance trial, 360 sea cucumbers (23±2g) were randomly assigned to 1 of 6 treatments. Each treatment was housed in 3 PVC tanks (38cm×54cm×80cm) with 20 sea cucumbers per tank. Six diets were prepared including an unsupplemented control diet, antibiotic treatment diet, 3 diets containing 1 of the 3 phages individually and a diet containing a cocktail of all 3 phages. After 60 days of feeding, all sea cucumber were challenged with V.splendidus VS-ABTNL by immersion in sea water containing a bacterial concentration of 6×10(6)CFU/mL for 2 days. The survival rate of sea cucumbers during the next 10 days was 18% for the unsupplemented diet, 82% for the antibiotic treatment, 82% for the phage cocktail, 65% for phage PVS-1, 58% for phage PVS-2 and 50% for phage PVS-3. There were no significant differences in weight gain, ingestion rate or feed conversion among sea cucumber fed the 4 phage treatments compared with those fed the unsupplemented diet (P>0.05). The levels of nitric oxide synthase and acid phosphatase of sea cucumbers fed phage-containing diets were significantly (P<0.05) increased compared with those fed the control diet. However, no significant differences (P>0.05) were detected among the 4 phage-fed treatments. An additional study was conducted in which 60 healthy sea cucumbers (23±2g) were randomly assigned to a control, an untreated group and a test group to investigate the effects of injecting phages by coelomic injection on the survival rate and enzyme activities in the coelomic fluid of the sea cucumbers. The control was injected with 1ml of sterilized seawater while the untreated group and the test group were injected with the same volume of V. splendidus-ABTNL culture (3×10(5)CFU/mL). Then, the test group was injected with 1ml of the 3 phage cocktail (MOI=10). After 48h, the activities of lysozyme, acid phosphatase and superoxide dismutase were elevated in the untreated group while the levels of these enzymes in the test group were similar to the blank control. After 10-day observation, the survival rate of the sea cucumber was 100% for the blank control, 80% for the test group and 20% for the negative control. The overall results of this experiment indicate that phage therapy increased the survival of sea cucumber infected with V.splendidus VS-ABTNL. The above results demonstrate that using phages, especially a combination of different phages, may be a feasible way to control Vibrio infection in the sea cucumber industry.

Soil suppressiveness by organic amendment to Fusarium disease in cucumber: effect on pathogen and host

Soil suppressiveness to Fusarium wilt and crown rot disease, caused by Fusarium oxysporum f. sp. radicis-cucumerinum in cucumber, develops following the incorporation of wild rocket (Diplotaxis tenuifolia (L.) DC.) crop residues, manifested as reduction in disease incidence. We studied mechanisms that might be involved in disease suppression. Exposure of nonamended-nonsuppressive soil to volatile organic compounds generated from wild rocket decomposing in the soil induced soil suppressiveness to Fusarium disease in nonamended soil. Similarly, a crude aqueous soil extract from wild rocket-amended (suppressive) soil induced suppressiveness to Fusarium disease when cucumber seedlings were transplanted into nonsuppressive soil amended with this soil extract. Suppressive soils did not show any effect on F. oxysporum f. sp. radicis-cucumerinum macroconidial germination, mycelium growth or new chlamydospore production. Root colonization with Fusarium spp. was suppressed in inoculated plants after 6 days, but not after 3 days. No evidence for induced resistance was found when plants were first grown in suppressive soil followed by inoculation and transplanting in nonsuppressive soil, or when plants were inoculated with Botrytis cinerea. Findings suggest that the microorganisms perpetuate the mechanisms of suppressiveness following the introduction of organic amendments, and that this occurs in the root zone.

Identification and characterisation of Dof transcription factors in the cucumber genome.

Cucumber is vulnerable to many foliage diseases. Recent studies reported cloning of candidate genes for several diseases in cucumber; however, the exact defence mechanisms remain unclear. Dof genes have been shown to play significant roles in plant growth, development, and responses to biotic and abiotic stresses. Dof genes coding for plant-specific transcription factors can promote large-scale expression of defence-related genes at whole genome level. The genes in the family have been identified and characterized in several plant species, but not in cucumber. In the present study, we identified 36 CsDof members from the cucumber draft genomes which could be classified into eight groups. The proportions of the CsDof family genes, duplication events, chromosomal locations, cis-elements and miRNA target sites were comprehensively investigated. Consequently, we analysed the expression patterns of CsDof genes in specific tissues and their response to two biotic stresses (watermelon mosaic virus and downy mildew). These results indicated that CsDof may be involved in resistance to biotic stresses in cucumber.

Loss-of-Function Mutations in CsMLO1 Confer Durable Powdery Mildew Resistance in Cucumber (Cucumis sativus L.).

Powdery mildew (PM) is a serious fungal disease of cucumber worldwide. The identification of resistance genes is very important for resistance breeding to ensure cucumber production. Here, natural loss-of-function mutations at an MLO homologous locus, CsMLO1, were found to confer durable PM resistance in cucumber. CsMLO1 encoded a cell membrane protein, was mainly expressed in leaves and cotyledons, and was up-regulated by PM at the early stage of host–pathogen interaction. Ectopic expression of CsMLO1 rescued the phenotype of the PM resistant Atmlo2 Atmlo12 double mutant to PM susceptible in Arabidopsis. Domesticated and wild resistant cucumbers originating from various geographical regions of the world were found to harbor three independent natural mutations that resulted in CsMLO1 loss of function. In addition, between the near-isogenic lines (NILs) of PM resistant and susceptible, S1003 and NIL(Pm5.1), quantitative RT-PCR revealed that there is no difference at expression levels of several genes in the pathways of ethylene, jasmonic acid or salicylic acid. Moreover, the two NILs were used for transcriptome profiling to explore the mechanism underlying the resistance. Several genes correlated with plant cell wall thickening are possibly involved in the PM resistance. This study revealed that loss of function of CsMLO1 conferred durable PM resistance, and that this loss of function is necessary but alone may not be sufficient for PM resistance in cucumber. These findings will facilitate the molecular breeding of PM resistant varieties to control this destructive disease in cucumber.

Fine mapping of a dominantly inherited powdery mildew resistance major-effect QTL, Pm1.1, in cucumber identifies a 41.1 kb region containing two tandemly arrayed cysteine-rich receptor-like protein kinase genes.

A dominantly inherited major-effect QTL for powdery mildew resistance in cucumber was fine mapped. Two tandemly arrayed cysteine-rich receptor-like protein kinase genes were identified as the most possible candidates. Powdery mildew (PM) is one of the most severe fungal diseases of cucumber (Cucumis sativus L.) and other cucurbit crops, but the molecular genetic mechanisms of powdery mildew resistance in cucurbits are still poorly understood. In this study, through marker-assisted backcrossing with an elite cucumber inbred line, D8 (PM susceptible), we developed a single-segment substitution line, SSSL0.7, carrying 95 kb fragment from PM resistance donor, Jin5-508, that was defined by two microsatellite markers, SSR16472 and SSR16881. A segregating population with 3600 F2 plants was developed from the SSSL0.7 × D8 mating; segregation analysis confirmed a dominantly inherited major-effect QTL, Pm1.1 in cucumber chromosome 1 underlying PM resistance in SSSL0.7. New molecular markers were developed through exploring the next generation resequenced genomes of Jin5-508 and D8. Linkage analysis and QTL mapping in a subset of the F2 plants delimited the Pm1.1 locus into a 41.1 kb region, in which eight genes were predicted. Comparative gene expression analysis revealed that two concatenated genes, Csa1M064780 and Csa1M064790 encoding the same function of a cysteine-rich receptor-like protein kinase, were the most likely candidate genes. GFP fusion protein-aided subcellular localization indicated that both candidate genes were located in the plasma membrane, but Csa1M064780 was also found in the nucleus. This is the first report of dominantly inherited PM resistance in cucumber. Results of this study will provide new insights into understanding the phenotypic and genetic mechanisms of PM resistance in cucumber. This work should also facilitate marker-assisted selection in cucumber breeding for PM resistance.

Mining candidate genes associated with powdery mildew resistance in cucumber via super-BSA by specific length amplified fragment (SLAF) sequencing.

BackgroundPowdery mildew (PM) is the most common fungal disease of cucumber and other cucurbit crops, while breeding the PM-resistant materials is the effective way to defense this disease, and the recent development of modern genetics and genomics make us aware of that studying the resistance genes is the essential way to breed the PM high-resistance plant. With the ever increasing throughput of next-generation sequencing (NGS), the development of specific length amplified fragment sequencing (SLAF-seq) as a high-resolution strategy for large-scale de novo SNP discovery is gradually applied for functional gene mining. Here we combined the bulked segregant analysis (BSA) with SLAF-seq to identify candidate genes associated with PM resistance in cucumber.MethodsA segregating population comprising 251 F2 individuals was developed using H136 (female parent) as susceptible parent and BK2 (male parent) as resistance donor. After PMR test, total genomic DNA was prepared from each plant. Systemic genomic analysis of the GC content, repeat sequence, etc. was carried out by prediction software SLAF_Predict to establish condition to ensure the uniformity and density of the molecular markers. After samples were gel purified, SLAFs were generated at Biomarker Technologies Corporation in Beijing. Based on SLAF tags and the PMR test result, the hot region were annotated.ResultsA total of 73,100 high-quality SLAF tags with an average depth of 99.11× were sequenced. Among these, 5,355 polymorphic tags were identified with a polymorphism rate of 7.34 %, including 7.09 % SNPs and other polymorphism types. Finally, 140 associated SLAFs were identified, and two main Hot Regions were detected on chromosome 1 and 6, which contained five genes invovled in defense response, toxin metabolism, cell stress response, and injury response in cucumber.ConclusionsAssociated markers identified by super-BSA in this study, could not only speed up the study of the PMR genes, but also provide a feasible solution for breeding the marker-assisted PMR cucumber. Moreover, this study could also be extended to any other species with reference genome.

Large-Scale Transcriptome Analysis of Cucumber and Botrytis cinerea during Infection.

Cucumber gray mold caused by Botrytis cinerea is considered one of the most serious cucumber diseases. With the advent of Hi-seq technology, it is possible to study the plant–pathogen interaction at the transcriptome level. To the best of our knowledge, this is the first application of RNA-seq to identify cucumber and B. cinerea differentially expressed genes (DEGs) before and after the plant–pathogen interaction. In total, 248,908,688 raw reads were generated; after removing low-quality reads and those containing adapter and poly-N, 238,341,648 clean reads remained to map the reference genome. There were 3,512 cucumber DEGs and 1,735 B. cinerea DEGs. GO enrichment and KEGG enrichment analysis were performed on these DEGs to study the interaction between cucumber and B. cinerea. To verify the reliability and accuracy of our transcriptome data, 5 cucumber DEGs and 5 B. cinerea DEGs were chosen for RT-PCR verification. This is the first systematic transcriptome analysis of components related to the B. cinerea–cucumber interaction. Functional genes and putative pathways identified herein will increase our understanding of the mechanism of the pathogen–host interaction.

A transposable element insertion in the susceptibility gene CsaMLO8 results in hypocotyl resistance to powdery mildew in cucumber.

BackgroundPowdery mildew (PM) is an important disease of cucumber (Cucumis sativus L.). CsaMLO8 was previously identified as a candidate susceptibility gene for PM in cucumber, for two reasons: 1) This gene clusters phylogenetically in clade V, which has previously been shown to harbour all known MLO-like susceptibility genes for PM identified in dicot species; 2) This gene co-localizes with a QTL on chromosome 5 for hypocotyl-specific resistance to PM.MethodsCsaMLO8 alleles from susceptible and resistant cucumber were cloned and transformed to mlo-mutant tomato. Cucumber seedlings were inoculated with Podosphaera xanthii, tissues were studied for CsaMLO8 expression at several timepoints post inoculation using qRT-PCR. The occurence of the observed loss-of-function allele of CsaMLO8 in resequenced cucumber accessions was studied in silico.ResultsWe cloned CsaMLO8 alleles from susceptible and resistant cucumber genotypes, the latter carrying the QTL for hypocotyl resistance. We found that insertion of a non-autonomous Class LTR retrotransposable element in the resistant genotype leads to aberrant splicing of CsaMLO8 mRNA. Heterologous expression of the wild-type allele of CsaMLO8 in a tomato mlo-mutant restored PM susceptibility. However, heterologous expression of the CsaMLO8 allele cloned from the resistant cucumber genotype failed to restore PM susceptibility. Furthermore we showed that inoculation of susceptible cucumber with the PM pathogen Podosphaera xanthii induced transcriptional upregulation of CsaMLO8 in hypocotyl tissue, but not in cotyledon or leaf tissue. This coincides with the observation that the QTL at the CsaMLO8-locus causes full resistance in hypocotyl tissue, but only partial resistance in cotyledons and true leafs. We studied the occurrence of the loss-of-function allele of CsaMLO8 in cucumber germplasm by an in silico approach using resequencing data of a collection of 115 cucumber accessions, and found that this allele was present in 31 out of 115 accessions.ConclusionsCsaMLO8 was characterised as a functional susceptibility gene to PM, particularly in the hypocotyl where it was transcriptionally upregulated upon inoculation with the PM pathogen P. xanthii. A loss-of-function mutation in CsaMLO8 due to the insertion of a transposable element was found to be the cause of hypocotyl resistance to PM. This particular allele of CsaMLO8 was found to occur in 27 % of the resequenced cucumber accessions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0635-x) contains supplementary material, which is available to authorized users.

Laporan Pertama Infeksi Begomovirus pada Tanaman Mentimun di Bali

Leaf yellowing symptoms was commonly found in cucumber plants in Bali provinces, i.e. in Apuan and Bangli villages recently. Begomovirus infection is suspected as the causal agent, due to similar symptoms previously reported from cucumber plants in Java. In addition, Bemisia tabaci was observed in the field. The objective of this research was to identify the causal agent of leaf yellowing disease of cucumber in Bali. Virus detection and identification was conducted by polymerase chain reaction method using universal primers for Begomovirus , i.e. SPG1/SPG2. DNA fragment of 912 bp in size was successfully amplified from leaf samples. Analysis of nucleotide sequencing indicated that Begomovirus infecting cucumber plants in Bali has the highest homology (91%) with Squash leaf curl China virus (SLCCNV) isolate from Malaysia. This is the first report of SLCCNV infection in Bali.

Fine genetic mapping of target leaf spot resistance gene cca-3 in cucumber, Cucumis sativus L.

The cucumber target leaf spot resistance gene cca - 3 was fine mapped in a 79-kb region harboring a CC-NB-ARC type R gene that may be responsible for the hypersensitive responses to infection of the target leaf spot pathogen in cucumber. The target leaf spot (TLS) is one of the most important foliar diseases in cucumber (Cucumis sativus L.). In this study, we conducted fine genetic mapping of a simply inherited recessive resistance gene, cca-3 against TLS with 193 F2:3 families and 890 F2 plants derived from the resistant cucumber inbred line D31 and the susceptible line D5. Initial mapping with microsatellite markers and bulked segregant analysis placed cca-3 in a 2.5-Mbp region of cucumber chromosome 6. The D5 and D31 lines were re-sequenced at 10× genome coverage to explore new markers in the target region. Genetic mapping in the large F2 population delimited the cca-3 locus in a 79-kb region with flanking markers Indel16874230 and Indel16953846. Additional fine mapping and gene annotation in this region revealed that a CC-NB-ARC type resistance gene analog, Csa6M375730, seems to be the candidate gene for cca-3. One single nucleotide polymorphism (SNP) was found in the NB-ARC domain of this candidate gene sequence between D31 and D5 that may lead to amino acid change, thus altering the function of the conserved NB-ARC motif. This SNP was validated in the segregating population as well as 24 independent cucumber lines. There was significantly higher level of cca-3 expression in the leaves of D5 (susceptible) than in D31 (resistant), and the expression level was positively correlated with the areas of necrotic spots on leaves after inoculation. It seems the cca-3 resistance gene was able to induce hypersensitive responses to the infection by TLS pathogen.