Disease Of Cucumber Research Articles

Biological control of soil borne cucumber diseases using green marine macroalgae

BackgroundIn this study, the potential of extracts and powders of green seaweeds, Ulva fasciata, and Enteromorpha flexuosa was evaluated as biocontrol against the pathogenic soil-borne fungi, Macrophomina phaseolina and Fusarium solani, infecting cucumber plants in Egypt. The antifungal activity of the algal extracts was evaluated in vitro against the pathogens mycelial fungal growth using five organic solvents.ResultsObtained results indicated that mycelial growth inhibition was noticed with F. solani in all algal extracts tested. In M. phaseolina, all algal extracts did not inhibit the fungal growth but affected microsclerotia formation (the main source of the second infection). In the case of F. solani, the highest reduction (68.6%) was noticed, while the chloroform extract of U. fasciata inhibited the radial growth of F. solani to 2.5 cm when E. flexuosa inhibited the radial growth to 4.3 cm as compared with the control (8.0 cm). The gas chromatography-mass spectrometry and the infrared spectroscopy analyses revealed that iron-monocarbonyl, cyclononasiloxane, and their functional groups, including amine, ether, etc., might play a core role in the anti-fungal activity of the seaweed extracts used.ConclusionThis work concluded that the macroalgae species with many unique antifungal properties components had an inhibitory effect against soil-borne cucumber diseases. The antimicrobial activity might be explored in the future in numerous diverse applications in agriculture and plant disease control, revealing their actions to control some plant fungal pathogens.

Effect of Temperature, Relative Humidity and Some Systemic Fungicides on Cucumber Downy Mildew and Certain Crop Parameters

Downy mildew caused by Pseudoperonospora cubensis (Berk. and Curt) Rostow is a major disease of cucumber (Cucumis sativus L.) in Egypt. The current study was carried out in Fayoum, Ismailia and Kafr Elsheikh Governorates in summer and fall during of 2018 and 2019 seasons. The effect of some whither parameters on downy mildew was studied. Temperature, relative humidity, disease severity and their relationships were determined. Five fungicides Previcur N 72.2 SL, Veulet 80 WP, Previcur Energy 840 SL, Infinito 68.75 SC and Profiler 71.1 WG, were used for the disease control. Final disease severity (FDS), area under disease progressive curve (AUDPC) and fungicides efficacy were measured and analyzed. Scanning electron microscope was used for histopathological studies. Fresh, dry weight and the average number of fruits/plant and fruit yield/feddan (ton) were recorded. Kafr Elsheikh recorded the lowest average temperature, being 23.8°Cduring the two growing seasons followed by Ismailia and Fayoum, being 25.2°C and 26.9°C, respectively. Kafr Elsheikh, also recorded the highest average of relative humidity, being 53.3% during the two growing seasons followed by Fayoum and Ismailia, being 52.9% and 51.9%, respectively. The same trend was observed for disease severity that recorded the highest average in Kafr Elsheikh, Ismailia and Fayoum 36.2, 31.45 and 30.9%, respectively during the two growing seasons. On the other hand, the lowest average temperature and the highest average of relative humidity were recorded in 2018 and 2019 seasons, respectively, while the highest averages of disease severity were recorded in 2018 and 2019 seasons, being 34.3 and 31.4, respectively. Fungicide, Infinito recorded the lowest FDS%, AUDPC and the highest efficacy%, being 6.6, 142.3 and, 7.0% and 171.8 in 2018 and 2019 seasons, respectively, followed by Profiler, Previcur Energy, Previcur N and Veulet. compared with control. Twisting, loss turgor, collapsing of sporangiophores and sporangium explosion were observed after application. Increasing and improvement of yield parameters were recorded.

Identification of Novel Loci and Candidate Genes for Resistance to Powdery Mildew in a Resequenced Cucumber Germplasm.

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.

Molecular characterization of recombinant Bipartite begomovirus associated with mosaic and leaf curl disease of Cucumber and Muskmelon

Muskmelon and cucumber are important vegetables grown in different parts of India. Leaf curl and mosaic diseases caused by begomovirus are economically important on these crops. Survey during 2012–2015 to assess the incidence of both leaf curl and mosaic in Mirzapur and Varanasi Districts of Eastern Uttar Pradesh, India revealed incidence of leaf curl up to 30–40% and mosaic disease up to 50–60% in both the crops. Totally, 103 leaf samples of muskmelon (58) and cucumber (45) were collected from the plants showing viral disease symptoms. These samples were tested for infection by different viruses using DAC-ELISA and PCR. A total of ten samples reacted for CGMMV, nine for PRSV-W, 25 for GBNV, 21 for CMV, 7 for ZYMV and 21 for DNA virus. Together, ELISA and PCR detected mixed infection of RNA viruses (CGMMV, CMV, PRSV-W and GBNV) and DNA virus in different combination in ten samples. The partial DNA virus genome (1.2 kb fragment) sequencing performed on samples indicated possible infection by a known bipartite begomovirus (Tomato leaf curl Palampur virus, ToLCPalV) in 21 samples. Therefore, one sample each from muskmelon (Mm-1) and cucumber (Cb-1) were used for full-length genome amplification of begomovirus genome using RCA method. Sequencing of the full-length viral genome (DNA A) and subsequent analysis using SDT program revealed that Mm-1 and Cb-1 isolates share a nucleotide (nt) identity of 90.4–92.2% and 95.9–99.1%, respectively with ToLCPalV infecting tomato and cucurbits. Similarly, analysis of full-length DNA B of Mm-1 and Cb-1 isolates indicated that they shared genome identity of 88.4–94.0% with tomato infecting ToLCPalV. Further, recombination breakpoint analysis of the viral genome indicated the recombinant nature of the virus isolates. The significance of ToLCPalV strains/variants as an emerging threat in the production of cucurbits in India is discussed.

A joint framework of feature reduction and robust feature selection for cucumber leaf diseases recognition

In machine learning (ML) domain, extracted features play a primary role in both segmentation and classification of salient/infected regions. Plants' diseases and pests are the main sources of colossal damage worldwide as they affect both the quality and quantity of crops. In China, cucumber is one of the main crops which is widely cultivated and has high economic benefits. Diseases like angular leaf spot, downy mildew, powdery mildew, etc., affect the cucumber crop and the only method being followed for its prevention is manual inspection. In this work, a hybrid framework based on feature fusion and selection techniques is proposed which classifies the cucumber diseases by using three core steps. Initialized with data augmentation, the contrast of image samples is enhanced in the first step, followed by feature extraction, fusion and selection in the second step. Finally, most discriminant features are classified using a set of classifiers. The extracted features in this work are initially reduced using the proposed probability distribution-based Entropy (PDbE) approach. After the serial-based fusion step, strong features are selected using the proposed Manhattan distance controlled entropy (MDcE) technique which has a capacity to select the features greater than a threshold. From the achieved accuracy (93.50 %) on the selected dataset having more than 900 image samples and six classes, it is very much evident that the presented method is comparable to several other existing techniques.

Isolation and characterization of antagonistic Paenibacillus polymyxa HX-140 and its biocontrol potential against Fusarium wilt of cucumber seedlings

ObjectiveThe aim of this study is to evaluate the efficacy of the strain Paenibacillus polymyxa HX-140, isolated from the rhizosphere soil of rape, to control Fusarium wilt of cucumber seedlings caused by Fusarium oxysporum f. sp. cucumerinum.ResultsStrain HX-140 was able to produce protease, cellulase, β-1,3-glucanase and antifungal volatile organic compounds. An in vitro dual culture test showed that strain HX-140 exhibited broad spectrum antifungal activity against soil-borne plant pathogenic fungi. Strain HX-140 also reduced the infection of Fusarium wilt of cucumber seedlings by 55.6% in a greenhouse pot experiment. A field plot experiment confirmed the biocontrol effects and further revealed that antifungal activity was positively correlated with inoculum size by the root-irrigation method. Here, inoculums at 106 107 and 108 cfu/mL of HX-140 bacterial suspension reduced the incidence of Fusarium wilt of cucumber seedling by 19.5, 41.1, and 50.9%, respectively.ConclusionsTaken together, our results suggest that P. polymyxa HX-140 has significant potential in the control of Fusarium wilt and possibly other fungal diseases of cucumber.

Economic efficiency of biological preparation application in protected ground vegetable growing

The paper describes the characteristics of biologic preparations and their application in protected ground conditions. In the course of the work, it was revealed that at present, vegetables are becoming more and more popular on the market, the use of chemicals in the their cultivation is limited. As a result of the experiment, the effectiveness of the use of biologic preparation Alirin-B and Gamair against diseases of protected soil cucumber and tomato was studied. The effectiveness of chemical and biological protection systems was compared, and the economic effect of their use was calculated.

The long-term colonization dynamics of endophytic bacteria in cucumber plants, and their effects on yield, fruit quality and Angular Leaf Spot Disease

Endophytic bacteria (EB) are ubiquitous in most plant species and they colonize plant tissues actively and systemically. Their colonization and persistence in the plant may be crucial to plant growth, yield and suppressing diseases. In this study, the long-term population dynamics of the two EB, namely Ochrobactrum spp. strain CB36/1 and Pantoea agglomerans strain CC37/2 in cucumber plants (Cucumis sativus L. cv. Gordion F1), were monitored. Also, the potential effects of these EB on plant growth, fruit quality, and yield, as well as the influences on Angular leaf spot disease of cucumber (ALS) and the yield under the disease pressure, were investigated. Plants were grown using the soilless cultivation technique in the greenhouse. Inoculation of the EB took place twice, and their population in plant tissues were monitored periodically for 62 days. Both EB isolates survived in plant organs until the end of the growing season, but over time, population densities dropped from 105 to 103 CFU g. plant−1 with the age of the plant. The EB applications had significant effects on fruit length, color and firmness. Total yield increased by 22% with CB36/1 and 21% with CC37/2 without disease pressure. Only CC37 / 2 significantly reduced the severity of ALS disease by 41% and increased yield by 22% compared to pathogen treatment alone. In this study, it was observed that the EB strain CC37/2 might contribute to reducing the chemical input and prevent the yield losses in soilless growing systems within the integrated agricultural concept.

Major cucumber diseases and the crop immunity

In Ukraine, cucumber (Cucumis sativus Linneus) annually occupies about 20 % of the total area of all vegetable crops sown in the open ground or 52.6 thousand hectares. The main reason that significantly reduces the quantitative and qualitative indicators of this vegetable crop's main valuable economic traits is the high incidence of commercial crops with diseases, especially downy mildew (Pseudoperonospora cubensis (Berk and M.A. Curtis) Rostovtsev). Since 1985 in Ukraine, this cucumber disease in the open ground on nonresistant varieties has continuously had intense development, in some years the development – by the type of epiphytotic. Simultaneously, the shortage of commercial yield of this vegetable crop due to the defeat of this disease under the field conditions can reach the level of 50–80 % or more, seed loss – 25–70 %. One of the main reasons for significant losses of commercial yield and seeds of gherkin cucumber under the conditions of its cultivation in the open ground is recognized as the high susceptibility of samples to some diseases, particularly downy mildew (Pseudoperonospora cubensis (Berk. and M.A. Curtis) Rostovtsev). Unfortunately, this problem has remained relevant for Ukraine over the past few decades. So, obtaining the initial material of a gherkin cucumber with a harmonious combination in the genotypes of a complex of various valuable economic characteristics (yield, quality, resistance to diseases, chemical substances content, suitability for various types of processing) and creating a modern competitive, innovative product (variety, hybrid) on its basis remains a relevant and priority task for domestic agricultural science at present. At the same time, scientists have proved that introducing complex (integrated) systems into production, which expect the biologization of protection with its transfer to an ecological and economic basis, is recognized as the most promising today. We suggested using resistant varieties (hybrids) in such integrated systems that provide the highest economic effect.

Identification of quantitative trait loci for powdery mildew resistance in highly resistant cucumber (Cucumis sativus L.) using ddRAD-seq analysis.

Powdery mildew, caused by Podosphaera xanthii (syn. Sphaerotheca fuliginea ex Fr. Poll.), is one of the most economically important foliar diseases in cucumber (Cucumis sativus L.). Cucumber parental line ‘Kyuri Chukanbohon Nou 5 Go’, developed from weedy cucumber line CS-PMR1, is highly resistant to powdery mildew and is promising breeding material. We performed quantitative trait locus (QTL) analysis using double-digest restriction-site-associated DNA sequencing (ddRAD-Seq) in a population from a cross between ‘Kyuri Chukanbohon Nou 5 Go’ and the Japanese native cultivar ‘Kaga-aonaga-fushinari’, which is susceptible to powdery mildew. The resistance of the population and its parents was evaluated using leaf disc assays and image analysis. We detected one major QTL on Chr. 5 that was effective at both 20°C and 25°C and one minor QTL on Chr. 1 effective at 20°C. We detected two additional QTLs in subpopulation: one on Chr. 3 effective at 20°C and one on Chr. 5 effective at both 20°C and 25°C in a position different from the major QTL. The resistance alleles at all four QTLs were contributed by ‘Kyuri Chukanbohon Nou 5 Go’. The results of this study can be used to develop practical DNA markers tightly linked to genes for powdery mildew resistance.

Blended Features Classification of Leaf‐Based Cucumber Disease Using Image Processing Techniques

Existing plant leaf disease detection approaches are based on features of extracting algorithms. These algorithms have some limits in feature selection for the diseased portion, but they can be used in conjunction with other image processing methods. Diseases of a plant can be classified from their symptoms. We proposed a cucumber leaf recognition approach, consisting of five steps: preprocessing, normalization, features extraction, features fusion, and classification. Otsu’s thresholding is implemented in preprocessing and Tan–Triggs normalization is applied for normalizing the dataset. During the features extraction step, texture and shape features are extracted. In addition, increasing the instances improves some characteristics. Through a principal component analysis approach, serial feature fusion is employed to provide a feature score. Fused features can be classified through a support vector machine. The accuracy of the Fine KNN is 94.30%, which is higher than the previous work in past papers.

Prevalence and harmfulness of the main cucumber diseases and crop immunity

Prevalence and harmfulness of the main cucumber diseases and crop immunity

Impact of Farm Management Practices on Downy Mildew Disease of Cucumber in High Tunnels

Downy mildew of cucumber caused by Pseudoperonospora cubensisis is a serious threat to the cucurbits production in high tunnels. In this study, the disease incidence and severity were recorded from nine high tunnel farms, located at Vehari District, Pakistan. The results revealed that downy mildew incidence was ranged from 24 to 80%. The disease development was correlated with plant genotype, sowing time, commonly used fungicides, and plant growth stages. "Kaan" was the most resistant while "Yayla" was the highly susceptible plant genotype against the disease. Cucumber sowing at mid-November showed significantly less disease over early and late sowing. Flowering was the most vulnerable stage of plants for disease development. ‘Champion’ (Copper hydroxide) followed by ‘Score’ (Difenoconazole) fungicides reduced the disease to 55% and 43%, respectively, which increased the yield 8-15 %. We conclude that the use of resistant genotype “Kaan”, protectant fungicide ‘Champion’ and appropriate sowing time Mid-November may reduce the disease incidence appreciably in high tunnels.

Fortified bacterial consortium – A novel approach to control root knot nematode in cucumber (cucumis sativum)

In present era of organic farming, biocontrol agents can be further improved to obtain greater levels of disease reduction. Development of formulations with increased shelf life and broad spectrum action with consistent performance under field conditions could pave the way for commercialization of the technology at a faster rate. In present investigation plant growth promoting rhizobacterial (PGPR) consortium containing three biocontrol bacterial strains (Providencia vermicola AAU PR1 (NCBI ACCN: KJ161325), Pseudomonas putida AAU PR2 (NCBI ACCN: KJ161326) and Pseudomonas fluorescens AAU PR3 (NCBI ACCN: KJ161327) fortified with extracts of botanicals viz. Azadirachta indica (neem), Ipomoea carnea (besharam) and Brassica juncea (mustard cake) was prepared and found to effectively control M. incognita under laboratory conditions and displayed highest reduction in egg hatching after 24, 48 and 72 h of exposure. Seed coating + soil drenching of fortified PGPR consortium was found to enhance plant growth parameters and reduce root knot nematode infestation in cucumber in pot experiment as well as field. Opinion of farmers growing cucumber in protected cultivation (polyhouse / greenhouse) indicated that application of fortified PGPR consortium reduced nematode infestation and replaced chemical measures of nematode control and showed increase in yield providing dual benefit of reducing cost of cultivation with higher yield. All the experimental results signified the efficiency of fortified PGPR consortium for control of root knot nematode disease in cucumber.

Biological control of fungi associated with damping-off and root rot disease of cucumber (Cucumis sativus L.)

Damping-off and root rot is a serious disease infecting cucumber on both seedling and adult stages. In this study, fifty-six fungal isolates were restored from cucumber plants showing typical symptoms of damping-off and root rot disease growing in different fields in Assiut governorate. These isolates were Pythium aphanidermatum (8 isolates), F. solani (12 isolates), Rhizoctonia solani (10 isolates), Drechslera halodes (12 isolates) and Macrophomina phaseolina (14 isolates). Pathogenicity tests revealed that these isolates were able to cause damping-off and root rot disease, however the most severe isolates were M. phaseolina isolate No 3 followed by R. solani No. 4, then F. solani isolate No. 6 as they caused root rot severity about 92.75, 91.5 and 76.75% respectively. In this study application of Gliocladium catenulatum, and Trichoderma harzianum proved to be an efficient antagonist to inhibit mycelial growth of plant pathogenic fungi in vitro, and to reduce the disease severity under greenhouse conditions, and significantly reduced the pre- and post-emergence damping off and root rot severity by rate of 50, 43.5, 52.33%, respectively in case of G. catenulatum and 60, 51.5, 53.32% in case of T. harzianum. These results proved that application of T. harzainum or G. catenulatum is an efficient method to control the causal pathogens of damping-off and root rot of cucumber.

Exploring the communities of bacteria, fungi and ammonia oxidizers in rhizosphere of Fusarium-diseased greenhouse cucumber

Long-term greenhouse vegetable cultivation commonly incurs soil-borne diseases, which seriously threaten the sustainability of greenhouse production system. Rhizomicrobiome plays an important role in ensuring plant health and driving soil nutrient cycling. However, how rhizomicrobiome respond to the occurrence of soil-borne disease is still not completely clear. Increasing knowledge involved would benefit to the prevention of soil-borne disease in intensive greenhouse production by providing the insight into soil microbial ecology. Herein, with the help of a continuously cultivated greenhouse cucumber field, soil physicochemical and biochemical properties and the abundances (quantitative real-time PCR) and communities (high-throughput amplicon sequencing) of bacteria, fungi, ammonia-oxidizing archaea (AOA) and bacteria (AOB) in the rhizosphere of healthy and Fusarium-diseased cucumbers were investigated. Diseased cucumber rhizosphere had significantly higher available nutrient contents and acidity compared to healthy cucumber rhizosphere, but significantly lower microbial activity and nitrification capacity. Although there was no significant difference in the abundances of bacteria, fungi, AOA and AOB, diseased cucumber rhizosphere had more abundant Fusarium oxysporum. For bacteria, only community richness in diseased cucumber rhizosphere was significantly lower than that in healthy cucumber rhizosphere, whereas for fungi both community richness and Shannon diversity were significantly lower. Community structures of bacteria, fungi, AOA and AOB all significantly differed between healthy and diseased cucumber rhizosphere. Particularly, healthy cucumber rhizosphere had more abundant beneficial microbes (Bacillus and Penicillium) and putative biocontrol microbes (Mycothermus) as well as Nitrosospira briensis Clade-related AOB. These results revealed significantly different rhizomicrobiome between Fusarium wilt diseased and healthy cucumbers under long-term intensive greenhouse cultivation, and suggested that rhizomicrobiome may play an important role in the occurrence of Fusarium wilt disease of cucumber. The findings obtained here also provided potential directions towards the prevention of soil-borne diseases and the improvement of N turnover in diseased soil by manipulating rhizosphere microbiome.

Identification of Novel Loci and Candidate Genes for Cucumber Downy Mildew Resistance Using GWAS.

Downy mildew (DM) is one of the most serious diseases in cucumber. Multiple quantitative trait loci (QTLs) for DM resistance have been detected in a limited number of cucumber accessions. In this study we applied genome-wide association analysis (GWAS) to detected genetic loci for DM resistance in a core germplasm (CG) of cucumber lines that represent diverse origins and ecotypes. Phenotypic data on responses to DM infection were collected in four field trials across three years, 2014, 2015, and 2016. With the resequencing data of these CG lines, GWAS for DM resistance was performed and detected 18 loci that were distributed on all the seven cucumber chromosomes. Of these 18 loci, only six (dmG1.4, dmG4.1, dmG4.3, dmG5.2, dmG7.1, and dmG7.2) were detected in two experiments, and were considered as loci with a stable effect on DM resistance. Further, 16 out of the 18 loci colocalized with the QTLs that were reported in previous studies and two loci, dmG2.1 and dmG7.1, were novel ones identified only in this study. Based on the annotation of homologous genes in Arabidopsis and pairwise LD correlation analysis, several candidate genes were identified as potential causal genes underlying the stable and novel loci, including Csa1G575030 for dmG1.4, Csa2G060360 for dmG2.1, Csa4G064680 for dmG4.1, Csa5G606470 for dmG5.2, and Csa7G004020 for dmG7.1. This study shows that the CG germplasm is a very valuable resource carrying known and novel QTLs for DM resistance. The potential of using these CG lines for future allele-mining of candidate genes was discussed in the context of breeding cucumber with resistance to DM.

Biological control of Pythium aphanidermatum-induced cucumber and radish damping-off by an endophytic fungus, Cladosporium omanense isolate 31R

ABSTRACT Cladosporium omanense has been recently described as a novel endophytic fungus from Zygophyllum coccineum in the desert habitat of Oman. The ability of this fungus to suppress Pythium aphanidermatum, the cause of cucumber and radish damping-off disease, was investigated. In vitro results showed effective suppression of P. aphanidermatum by C. omanense, producing an inhibition zone of 3.67 mm in dual culture assay. Light microscope and scanning electron microscope examination showed abnormalities in Pythium hyphae at the inhibition zone. The culture filtrate from C. omanense induced cellular leakage from Pythium mycelium and inhibited oospore production. A bioassay test was further conducted to examine the ability of C. omanense in suppressing P. aphanidermatum-induced damping-off disease of cucumber. It showed that C. omanense significantly increased the percent surviving cucumber seedlings up to 58.9%. Similarly, the addition of C. omanense significantly increased the percent surviving radish seedlings up to 80.4%. The in vivo and in vitro suppression effects of C. omanense were mainly due to the production of cellulase, β-1,3-glucanases and siderophores in the culture filtrate of C. omanense. This is the first report describing the biocontrol efficacy of C. omanense, especially in suppressing P. aphanidermatum-induced damping-off of cucumber and radish.

A single gene in Fusarium oxysporum limits host range.

Fusarium oxysoporum f. sp. radicis‐cucumerinum (Forc) is able to cause disease in cucumber, melon, and watermelon, while F. oxysporum f. sp. melonis (Fom) can only infect melon plants. Earlier research showed that mobile chromosomes in Forc and Fom determine the difference in host range between Forc and Fom. By closely comparing these pathogenicity chromosomes combined with RNA‐sequencing data, we selected 11 candidate genes that we tested for involvement in the difference in host range between Forc and Fom. One of these candidates is a putative effector gene on the Fom pathogenicity chromosome that has nonidentical homologs on the Forc pathogenicity chromosome. Four independent Forc transformants with this gene from Fom showed strongly reduced or no pathogenicity towards cucumber, while retaining pathogenicity towards melon and watermelon. This suggests that the protein encoded by this gene is recognized by an immune receptor in cucumber plants. This is the first time that a single gene has been demonstrated to determine a difference in host specificity between formae speciales of F. oxysporum.

Application of spent mushroom substrate suppresses Fusarium wilt in cucumber and alters the composition of the microbial community of the cucumber rhizosphere

One of the main cucumber (Cucumis sativus) diseases in China is Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. cucumerinum (FOC). The aims of this study were to evaluate the suppressive capacity of different spent mushroom substrate (SMS) amendments against Fusarium wilt and to analyse their effects on soil microbiological properties. A greenhouse experiment was carried out with four treatments: (1) CK: unamended control, (2) FV: application of spent Flammulina velutipes substrate, (3) LE: application of spent Lentinus edodes substrate, and (3) PO: application of spent Pleurotus ostreatus substrate. Cucumber disease incidence, the abundance of FOC, Bacillus, Pseudomonas and Lysobacter (using real-time PCR), and the microbial community (using Biolog EcoPlate and phospholipid fatty acid (PLFA) analyses) in rhizosphere were studied 15, 30, 45 and 60 days after transplantation. At the end of the 60-day pot experiment, the FV, LE and PO treatments significantly (p < 0.05) reduced disease incidence by 53.3%, 25.7% and 37.9%, respectively, compared to the CK treatment. All three SMS amendments significantly (p < 0.05) increased the growth of cucumber seedlings and suppressed the FOC population compared to the control. The three SMS amendments, in particular spent F. velutipes substrate, increased the abundance of beneficial microbes (Bacillus spp., Pseudomonas spp. and Lysobacter spp.). Biolog and PLFA data showed that average well colour development (AWCD), total PLFAs, bacterial, and Gram (+) and Gram (−) bacterial PLFAs were increased in the FV, LE and PO treatments. Overall, the results of this study suggest that the application of three SMS amendments, especially FV, could effectively suppress cucumber Fusarium wilt and reducing the population of FOC.