Susceptible Cucumber Cultivars Research Articles

Exogenous priming of chitosan induces upregulation of phytohormones and resistance against cucumber powdery mildew disease is correlated with localized biosynthesis of defense enzymes

In recent years, exploration of biopolymer-based materials to avoid hazardous chemicals in agriculture has gained enormous importance for sustainable crop improvement. In the present study, chitosan a biopolymer derived from crab-shell was used in different concentrations as priming agent to cucumber seeds and were evaluated for its effect to enhance plant growth parameters as well as its ability to induce resistance against powdery mildew disease. Among the treatments, seeds-primed with 2.5 mg/mL exhibited early seedling germination of 90% and vigour of 2665 and also remarkably enhanced the cucumber growth parameters which might be fairly attributed to the stimulation of phytohormones content in primed plants over the controls. More importantly, under greenhouse conditions a significant induced disease protection of 66.6% against powdery mildew disease was noticed in chitosan-pretreated plants at 2.5 mg/mL. The induced resistant plants also showed a significant deposition of lignin, callose and H2O2. Notably, polyphenol oxidase, phenylalanine ammonia-lyase, peroxidase and glucanase defense-responsive enzymes were upregulated in chitosan-primed plants. Considered together, these results determine that the susceptible cucumber cultivar elicits immunity after perception of priming with chitosan to upregulate phytohormones and synthesize defense-responsive enzymes, thereby induce resistance against powdery mildew disease and strengthen the growth-promotion of cucumber plants.

Management of powdery mildew on greenhouse cucumber (Cucumis sativus L.) plants using biological and chemical approaches

Powdery mildew, caused by Podosphaera xanthii (U. Braun & Shishkoff), is a widespread disease on greenhouse cucumber in many countries, including Canada. The efficacy of seven biological or chemical products to manage powdery mildew was evaluated. These included Rhapsody® (Bacillus subtilis Ehrenberg strain QST 713), Microflora PROTM (B. subtilis, Bacillus amyloliquefaciens Priest et al., Bacillus pumilus Meyer & Gottheil), Prestop® (Gliocladium catenulatum J.C. Gilman & E.V. Abbott strain J1446), Double Nickel LC (B. amyloliquefaciens strain D747), Active Flower™ (fertilizer containing N:P:K of 8:4:12 plus 3% boron), Luna® (fluopyram and pyrimethanil) and Pristine® (pyraclostrobin and boscalid). Products were applied as preventative or eradicative treatments at weekly intervals to the moderately susceptible cucumber cultivars ‘Picowell RZ’ or ‘Tasty Green’. Disease severity was rated after 3–4 applications as the number of colonies that developed on leaves, or as a percentage of leaf area infected calculated using image analysis. Rhapsody at a rate of 1.5% provided the most significant disease reduction compared with the other three biological products, although rates of 2% and 4% also resulted in high disease suppression in a second experiment. The fungicides Luna (0.5 mL L−1) and Pristine (0.66 g L−1) provided a level of control comparable to Rhapsody. Application of ActiveFlower at 0.5 and 0.3 mL 100 mL−1 significantly reduced powdery mildew after three applications, but some phytotoxicity was observed at the higher rate. The products tested in this study can be part of an integrated powdery mildew management programme for greenhouse cucumber.

Cucumber mosaic virus resistance: Comparative proteomics of contrasting Cucumis sativus cultivars after long-term infection

Plant viruses are a significant threat to a wide range of host species, causing substantial losses in agriculture. Particularly, Cucumber mosaic virus (CMV) evokes severe symptoms, thus dramatically limiting yield. Activation of plant defense reactions is associated with changes in the cellular proteome to ensure virus resistance. Herein, we studied two cultivars of cucumber (Cucumis sativus) resistant host Heliana and susceptible host Vanda. Plant cotyledons were mechanically inoculated with CMV isolate PK1, and systemic leaves were harvested at 33 days post-inoculation. Proteome was profiled by ultrahigh-performance liquid chromatography and comprehensively quantified by ion mobility enhanced mass spectrometry. From 1516 reproducibly quantified proteins using a label-free approach, 133 were differentially abundant among cultivars or treatments by strict statistic and effect size criteria. Pigments and hydrogen peroxide measurements corroborated proteomic findings. Comparison of both cultivars in the uninfected state highlighted more abundant photosynthetic and development-related proteins in resistant cucumber cultivar. Long-term CMV infection caused worse preservation of energy processes and less robust translation in the susceptible cultivar. Contrary, compatible plants had numerous more abundant stress and defense-related proteins. We proposed promising targets for functional validation in transgenic lines: A step toward durable virus resistance in cucurbits and other crops. SignificanceSustainable production of crops requires an understanding of natural mechanisms of resistance/susceptibility to ubiquitous viral infections. We report original findings of comparative analysis of plant genotypes exposed to CMV. Deep discovery proteomics of resistant and susceptible cucumber cultivars, inoculated with widespread phytovirus, allowed to suggest several novel molecular targets for functional testing in plant protection strategies.

Interactions of Acariphagous Arthropods in the System “Host Plant—Spider Mite Tetranychus urticae Koch (Acarina, Tetranychidae)—Predatory Mite Phytoseiulus persimilis Ath.-H. (Parasitiformes, Phytoseiidae) and Predatory Midge Feltiella luboviae Fedotova et Kozlova (Diptera, Cecidomyiidae)” on Cucumber Cultivars

Relations between the predatory species were studied in the tritrophic system “plant—spider mite Tetranychus urticae—predatory mite Phytoseiulus persimilis + predatory gall midge Feltiella luboviae” on Ginga F1 and Muromsky 36 cucumber cultivars, differing in their resistance to the phytophage. It was shown that the formation and functioning of the consortium were largely influenced by the resistance properties of the cucumber cultivars and the bioecological features of the consorts. The acariphages most effectively suppressed the pest at the initial stage of consortium formation, when their first generation was active. The efficiency of the predatory midge F. luboviae on the susceptible cucumber cultivar was lower in the presence of the predatory mite Ph. persimilis. The resistant cultivar not only compensated for the negative effect of one predator (Ph. persimilis) on the oviposition behavior of the other predator (F. luboviae), but also increased the efficiency of combined use of the acariphages as compared to their separate application.

Genetic mapping of angular leaf spot resistance to Pseudomonas syringae pv. lachrymans in a Cucumis hystrix introgression line of cucumber

Angular leaf spot (ALS), caused by Pseudomonas syringae pv. lachrymans, is a common and devastating bacterial disease of cucumber worldwide. However, to the best of our knowledge, the report on genetic mapping of ALS resistance in cucumber is relatively few. In this study, IL52, a Cucumis hystrix introgression line of cucumber, was identified to be resistant to ALS. To investigate the inheritance and genomic location of the ALS resistance gene, IL52 was crossed with a susceptible parent changchunmici (CCMC) to develop F1 plant and 155 F6 recombinant inbred lines (RILs). The F1 plant was susceptible to ALS. The segregation ratio of ALS disease resistance in 155 RILs was 80:75 resistance/susceptibility, fitting to 1:1. The results indicated that a single recessive locus psl-1 was responsible for conferring resistance to ALS in IL52. Further, psl-1 was mapped into the 3,118,855–3,951,558 bp interval of chromosome 1 by combining molecular mapping with bulked segregant analysis and next-generation sequencing (BSA-seq). The marker ALS-InDel was found to be closely linked with psl-1 through the genetic linkage analysis in the 18 resistant RILs, 18 susceptible RILs and 19 susceptible cucumber cultivars. This study on genetic mapping of ALS resistance gene in a Cucumis hystrix introgression line of cucumber will be helpful for fine mapping and marker-assisted selection of ALS resistance gene.

GROWTH AND YIELD RESPONSES OF FIFTEEN CUCUMBER CULTIVARS TO ROOT-KNOT NEMATODE (Meloidogyne incognita)

Root-knot nematodes have become a grave menace to the lucrative production of cucumber throughout the world. These nematodes are mainly controlled by applying nematicides, but their use is often associated with hazards. Alternatively, the use of nematode resistant cultivars is considered to be innocuous and economically feasible. For their fitness as nematode-suppressive crops, the reduction in growth and yield parameters of these cultivars must be assessed. As there is little documented data about the effects of Meloidogyne incognita on the damage of cucumber, therefore, in the present study, the effects of M. incognita were evaluated on growth and yield parameters of fifteen cucumber cultivars. M. incognita significantly negatively affected the growth and yield parameters of all the cucumber cultivars. Shoot and root lengths and shoot weights of all the cultivars were significantly reduced as a result of nematode infection. Maximum reductions in these parameters were recorded in highly susceptible cultivars followed by susceptible ones, while the reductions were minimal in resistant followed by moderately resistant cultivars. On the contrary, the infection by M. incognita resulted in an increase in root weights of all the cultivars. The increase was found to be the maximum in highly susceptible cultivars followed by susceptible and moderately susceptible cultivars. Likewise, the minimum increase was observed in the resistant cultivars followed by moderately resistant cultivars. Similarly, significant variations in yield parameters among fifteen cucumber cultivars were also recorded as a result of M. incognita infection. In the case of highly susceptible cultivars, the reductions in yield parameters were maximum, whereas the reductions in resistant and moderately resistant cultivars were found to be minimum. As cultivars Long Green, Marketmore, Pioneer-II, Dynasty and Summer Green experienced no significant damage compared to susceptible cucumber cultivars and therefore, they are approved for cultivation in nematode infested soils.

Long-term feeding on greenhouse cucumber affects life table parameters of two-spotted spider mite and its predator Phytoseiulus persimilis

Bio-ecological parameters of the two-spotted spider mite (TSSM), Tetranychus urticae Koch and its predators depend on the quality of its host plants. In this study, the life table parameters of TSSM and its main predator Phytoseiulus persimilis Athias-Henriot during different generations (1st, 5th, and 10th generations) were determined on the susceptible (‘Beth-Alpha’) and resistant (‘HED’) greenhouse cucumber cultivars. The results indicated that the longest total development time of TSSM was allocated to the first generation on the susceptible cultivar, but there was no significant difference among different generations on the resistant cultivar. The total development time of the 1st and 10th generations of P. persimilis on each of the susceptible and resistant cultivars had not significant difference. Total fecundity of TSSM was higher in the 10th generation on both cultivars tested than that of the former generations. However, the total fecundity of the predator drastically reduced after long-term rearing (10 generations) on both cultivars. The intrinsic rate of increase (r) of the 1st, 5th, and 10th generations of TSSM on the susceptible cultivar was 0.178, 0.238 and 0.319 day-1, respectively, and 0.157, 0.166 and 0.168 day-1 on the resistant cultivar, respectively which indicates the significantly negative effect of the resistant cultivar on this parameter. In P. persimilis, the value of the intrinsic rate of increase in the first and tenth generations on the susceptible cultivar was 0.275 and 0.267 day-1, respectively, and on the resistant cultivar was 0.244 and 0.210 day-1, respectively. By understanding these interactions in the long term, we will be able to develop suitable strategies for biological control of TSSM on cucumber.

Serial passage through resistant and susceptible cucumber cultivars affects the virulence of Fusarium oxysporum f. sp. cucumerinum.

Fusarium oxysporum f. sp. cucumerinum (Foc) is the causal pathogen of cucumber Fusarium wilt resulting in losses to cucumber production. To investigate the effects of the selective pressures of host plants on the virulence of Foc, a low virulence isolate, foc‐3b, was successively inoculated on resistant and susceptible cucumber cultivars for five generations. The virulence of the original isolate diverged; virulence was significantly strengthened after serial passage on the resistant cultivar and weakened on the susceptible plants (p ˂ .05). The expression of four virulence‐related genes of F. oxysporum, G‐protein α subunit gene fga1, sucrose nonfermenting 1 gene snf1, F‐box protein gene frp1, and Class V chitin synthase gene chsV, was quantified using real‐time PCR. All genes were significantly upregulated after serial passage on the resistant cultivar, compared to the original strain, and the expression of snf1 was downregulated in strains re‐isolated from the susceptible plants (p ˂ .05). A significant positive correlation was found between the expression levels of gene snf1, frp1, and chsV and disease severity of cucumber Fusarium wilt, suggesting these genes may impact virulence differentiation. This study will improve the management of cucumber Fusarium wilt and provide insight into the mechanisms underlying virulence of F. oxysporum.

Expression and functional analysis of the transcription factor-encoding Gene CsERF004 in cucumber during Pseudoperonospora cubensis and Corynespora cassiicola infection

BackgroundCucumber downy mildew, caused by P. cubensis, is an important leaf disease that can severely affect cucumber production. In recent years, cucumber target spot, caused by C. cassiicola, has been reported in both Asia and Europe and is now considered as a major disease disrupting cucumber production. Single-disease-resistant cucumber varieties have been unable to satisfy production needs.To explore the molecular mechanisms of cucumber resistance to these two diseases, cucumber cultivars D9320 (resistant to downy mildew and target spot) and D0401 (susceptible to downy mildew and target spot) were used as experimental materials in this study. We used transcriptome sequencing technology to identify genes related to disease resistance and verified using transgenic technology.ResultsWe screened out the cucumber resistance-related gene CsERF004 using transcriptome sequencing technology. Induction by pathogens, salicylic acid (SA), and ethylene (ET) resulted in the up-regulation of CsERF004. Three treatments, namely, inoculation with C. cassiicola alone, inoculation with P. cubensis alone, and simultaneous inoculation with both pathogens, all resulted in the significant and sustained up-regulation of CsERF004 in the resistant cultivar D9320, during the early stage of infection. In the susceptible cultivar D0401, CsERF004 expression was also significantly up-regulated at the later stage of infection but to a lesser extent and for a shorter duration than in the resistant cultivar D9320. The CsERF004 gene encodes a protein localizes to the nucleus. The over-expression of CsERF004 in the susceptible cultivar D0401 resulted in the significant up-regulation of the CsPR1 and CsPR4 genes and increased the levels of SA and ET, which enhanced the resistance of cucumber to downy mildew and target spot.ConclusionsAnalyses of the CsERF004 expression pattern in disease-resistant and susceptible cucumber cultivars and transgenic validation indicate that CsERF004 confers resistance to P. cubensis and C. cassiicola. The findings of this study can help to better understanding of mechanisms of response to pathogens and in establishment the genetic basis for the development of cucumber broad-spectrum resistant cultivars.

Differential expression of cucumber RNA-dependent RNA polymerase 1 genes during antiviral defence and resistance.

RNA-dependent RNA polymerase 1 (RDR1) plays a crucial role in plant defence against viruses. In this study, it was observed that cucumber, Cucumis sativus, uniquely encodes a small gene family of four RDR1 genes. The cucumber RDR1 genes (CsRDR1a, CsRDR1b and duplicated CsRDR1c1/c2) shared 55%-60% homology in their encoded amino acid sequences. In healthy cucumber plants, RDR1a and RDR1b transcripts were expressed at higher levels than transcripts of RDR1c1/c2, which were barely detectable. The expression of all four CsRDR1 genes was induced by virus infection, after which the expression level of CsRDR1b increased 10-20-fold in several virus-resistant cucumber cultivars and in a broad virus-resistant transgenic cucumber line expressing a high level of transgene small RNAs, all without alteration in salicylic acid (SA) levels. By comparison, CsRDR1c1/c2 genes were highly induced (25-1300-fold) in susceptible cucumber cultivars infected with RNA or DNA viruses. Inhibition of RDR1c1/c2 expression led to increased virus accumulation. Ectopic application of SA induced the expression of cucumber RDR1a, RDR1b and RDRc1/c2 genes. A constitutive high level of RDR1b gene expression independent of SA was found to be associated with broad virus resistance. These findings show that multiple RDR1 genes are involved in virus resistance in cucumber and are regulated in a coordinated fashion with different expression profiles.

The expression patterns of Cucumis sativus WRKY (CsWRKY) family under the condition of inoculation with Phytophthora melonis in disease resistant and susceptible cucumber cultivars

Xu, X., Wang, R., Chao, J., Lin, Y., Jin, Q., He, X., Luo, S. and Wu, T. 2015. The expression patterns of Cucumis sativus WRKY (CsWRKY) family under the condition of inoculation with Phytophthora melonis in disease resistant and susceptible cucumber cultivars. Can. J. Plant Sci. 95: 1121–1131. Based on RNA-seq, we analyzed expression patterns of 55 CsWRKYs in the disease-resistant cultivar (JSH) and the disease-susceptible cucumber cultivar (B80) at 0 and 40 h post-inoculation with Phytophthora melonis. After inoculation with P. melonis, in JSH and B80, the number of up-regulated CsWRKY genes was both 25 with 22 commonly up-regulated genes, and there were 22 CsWRKY genes down-regulated in JSH and 23 in B80 with 18 commonly down-regulated genes, and there were eight CsWRKY genes with no or little change in transcript expression in JSH and seven in B80 with four common genes. Among the 55 CsWRKY genes, 17 genes showed significant differences (differences > twofold) in the degree of change of gene transcription level between JSH and B80 from RNA-seq data analysis, and the results validated using real-time PCR showed that there were only six genes (CsWRKY2, 20, 26, 35, 44, 52) out of the 17 that exhibited significant differences (differences > twofold) with four genes (CsWRKY2, 20, 26, 52) consistent with the data from RNA-seq and two genes (CsWRKY 35, 44) inconsistent with the data from RNA-seq. In addition, the six genes were strongly up-regulated after salicylic acid (SA) treatment with five genes (CsWRKY2, 20, 26, 35, 44) up to peak at 12 h and one gene (CsWRKY52) up to peak at 24 h in expression and that four CsWRKY genes (CsWRKY2, 20, 44, 52) out of six were strongly up-regulated with three genes (CsWRKY2, 20, 44) up to the highest point at 24 h and one gene (CsWRKY52) up after methyl jasmonate (MeJA) treatment. Based on the results above, we predicted CsWRKY2, 20, 26, 35, 44 and 52 may be involved in disease resistance of JSH against Phytophthora melonis by SA and (or) JA signaling pathway(s).

The expression patterns of Cucumis sativus WRKY (CsWRKY) family under the condition of inoculation with Phytophthora melonis in disease resistant and susceptible cucumber cultivars

Xu, X., Wang, R., Chao, J., Lin, Y., Jin, Q., He, X., Luo, S. and Wu, T. 2015. The expression patterns of Cucumis sativus WRKY (CsWRKY) family under the condition of inoculation with Phytophthora melonis in disease resistant and susceptible cucumber cultivars. Can. J. Plant Sci. 95: 1121-1131. Based on RNA-seq, we analyzed expression patterns of 55 CsWRKYs in the disease-resistant cultivar (JSH) and the disease-susceptible cucumber cultivar (B80) at 0 and 40 h post-inoculation with Phytophthora melonis. After inoculation with P. melonis, in JSH and B80, the number of up-regulated CsWRKY genes was both 25 with 22 commonly up-regulated genes, and there were 22 CsWRKY genes down-regulated in JSH and 23 in B80 with 18 commonly down-regulated genes, and there were eight CsWRKY genes with no or little change in transcript expression in JSH and seven in B80 with four common genes. Among the 55 CsWRKY genes, 17 genes showed significant differences (differences > twofold) in the degree of change of gene transcript...

Studies on Fusarium wilt Disease of Cucumber

Eight isolates of Fusarium oxysporum f.sp. cucumerinum; the causal organism of Fusarium wilt of cucumber plants; were isolated from wilted cucumber plant samples collected from eight different localities in Egypt . These isolates were pathogenic to the susceptible cucumber cultivar “Biet alpha”. Isolate 3 was the most virulent, followed by isolate 4 , while the least pathogenic was isolate 5. Potato Dextrose medium was the best medium for linear and amount of growth for all tested isolates, whereas rate of growth varied between the different tested isolates with the different tested media. Optimum temperature for the fungal linear growth was 27°C, followed by 28°C, while the best amount of growth was obtained at 25°C for all tested isolates. Cucumber genotypes were susceptible to Fusarium oxysporum f.sp. cucumerinum and differed significantly in their susceptibility. The most tolerant cucumber genotype was “Zeina” as well as it recorded the highest survival plants. DNA analysis detected 33 loci with an average 4.125 loci/isolate. The highest number of polymorphic loci was 6 loci in both Fus 1&4 isolates, while the lowest was 1 loci in Fus 6 only. UPGMA cluster analysis divide into two sub clusters, one of them included Fus 6 only and the second include the rest seven isolates with different similarity values. 100 & 614 bp were detected in both highly pathogenic isolates and it could be carrying the genetic information affecting pathogenicity of Fusarium to cucumber plants. Grouping of Trichoderma isolates in UPGMA cluster analysis and variation in DNA profiles among isolates was not related to their biocontrol ability. Biocontrol agents great affected Fusarium growth in dual cultures and reduced it under laboratory conditions. Biocontrol agents minimized the disease parameters in comparing with infested control treatments by the most aggressive isolate under greenhouse condition.

Cucumis sativus L-type lectin receptor kinase (CsLecRK) gene family response to Phytophthora melonis, Phytophthora capsici and water immersion in disease resistant and susceptible cucumber cultivars

L-type lectin receptor kinase (LecRK) proteins are an important family involved in diverse biological processes such as pollen development, senescence, wounding, salinity and especially in innate immunity in model plants such as Arabidopsis and tobacco. Till date, LecRK proteins or genes of cucumber have not been reported. In this study, a total of 25 LecRK genes were identified in the cucumber genome, unequally distributed across its seven chromosomes. According to similarity comparison of their encoded proteins, the Cucumis sativus LecRK (CsLecRK) genes were classified into six major clades (from Clade I to CladeVI). Expression of CsLecRK genes were tested using QRT-PCR method and the results showed that 25 CsLecRK genes exhibited different responses to abiotic (water immersion) and biotic (Phytophthora melonis and Phytophthora capsici inoculation) stresses, as well as that between disease resistant cultivar (JSH) and disease susceptible cultivar (B80). Among the 25 CsLecRK genes, we found CsLecRK6.1 was especially induced by P. melonis and P. capsici in JSH plants. All these results suggested that CsLecRK genes may play important roles in biotic and abiotic stresses.

Analysis of the defence-related mechanism in cucumber seedlings in relation to root colonization by nonpathogenic Fusarium oxysporum CS-20.

A defence response can be induced by nonpathogenic Fusarium oxysporum CS-20 in several crops, but the molecular mechanism has not been clearly demonstrated. In the present study, we analysed the defence mechanism of a susceptible cucumber cultivar (Cucumis sativus L. 9930) against a pathogen (F. oxysporum f. sp. cucumerinum) through the root precolonization of CS-20. A challenge inoculation assay indicated that the disease severity index (DSI) was reduced, ranging from 18.83 to 61.67 in comparison with the pathogen control. Root colonization analysis indicated that CS-20 clearly did not appear to influence the growth of cucumber seedlings. Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) revealed that CS-20-mediated defence response was activated by PR3, LOX1 and PAL1 and the pathogen-mediated resistance response was regulated by PR1 and PR3. Moreover, both nonpathogenic and pathogenic F. oxysporum were able to upregulate NPR1 expression. In contrast to a pathogen, CS-20 can activate the Ca(2+) /CaM signal transduction pathway, and the gene expression of both CsCam7 and CsCam12 increased significantly. The gene expression analysis indicated that CS-20 strongly enhanced the expression of PR3, LOX1, PAL1, NPR1, CsCam7 and CsCam12 after inoculation. Overall, the defence response induced by CS-20 can be controlled by multiple genes in the cucumber plant.

Elevated expression of hydrolases, oxidase, and lyase in susceptible and resistant cucumber cultivars systemically induced with plant growth-promoting fungi against anthracnose

Susceptible and resistant cultivars of cucumber (cv. Suyo and cv. Shogoin fushinari, respectively) were evaluated for induction of systemic resistance by plant growth-promoting fungal isolates Phoma sp. GS8-1 and nonsporulating fungus GU21-2 against Colletotrichum orbiculare. Reduction in anthracnose disease was assessed at regular intervals of 0, 3, 6, and 9 days after challenge inoculation. Activities of endochitinase, β-1,3-endoglucanase, peroxidase (PO), polyphenol oxidase, and phenylalanine ammonia lyase (PAL) were assayed at the above intervals, while the activities of exochitinase and β-1,3-exogluconase were assayed at 9 days after challenge inoculation. The data showed that all the enzymes activities increased in plants treated with plant growth-promoting fungi (PGPF) compared with nontreated plants of both cultivars. The activities of endochitinase and β-1,3-endoglucanase were highly increased in PGPF-induced plants than in nontreated plants of both cultivars at different time points. Activities of PO, polyphenol oxidase, and PAL also increased between 3 and 6 days due to inoculation with PGPF and decreased thereafter. The activity of PAL at 9 days in PGPF-induced plants was at the same level as that of nontreated plants of both cultivars. Results of this investigation suggest that PGPF-induced systemic resistance is associated with not only high increases in the activities of chitinase and β-1,3-gluconases but also other plant defense-related enzymes such as PO, PPO, and PAL. Roles of other mechanisms rather than accumulation of defense-related enzymes in PGPF-mediated induced resistance in susceptible cultivars were demonstrated.

PRELIMINARY SCREENING OF INDIGENOUS BACTERIAL ISOLATES FROM SOIL AND FISH POND SEDIMENTS FOR THEIR BENEFICIAL EFFECT ON VEGETABLES GROWTH AND HEALTH

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Environmental, Edaphic, and Genetic Factors Affecting Plants, Seeds and Turfgrass PRELIMINARY SCREENING OF INDIGENOUS BACTERIAL ISOLATES FROM SOIL AND FISH POND SEDIMENTS FOR THEIR BENEFICIAL EFFECT ON VEGETABLES GROWTH AND HEALTH

Cucumber vein yellowing virus isolate-specific expression of symptoms and viral RNA accumulation in susceptible and resistant cucumber cultivars

Since its outbreak in Spain during the fall of 2000, Cucumber vein yellowing virus (CVYV) has become into a limiting factor in cucurbit cultivation in this country, particularly in cucumber. The impact of the virus has been limited after the introduction of resistant cucumber cultivars and the implementation of cultural practices to control whitefly, the virus vector. In Spain, CVYV isolates are genetically similar and cucumber resistance breaking isolates have not been reported. A CVYV isolate from Jordan (Jor) was previously reported as being more virulent in cucumber cv. Beit Alfa than an isolate from Israel. To study the reactions of different cucumber cultivars to the virulent Jor isolate in comparison with a Spanish isolate of (Alm 1A), we have inoculated both isolates in 10 commercial cucumber cultivars with resistance to the virus. Also, we have used real-time RT-PCR to estimate virus accumulation of Jor and Alm 1A isolates in three of these cultivars, one described as susceptible and two as resistant to CVYV. The Spanish Alm 1A isolate caused mild or no symptoms in resistant cultivars whereas Jor isolate caused intense symptoms in all cultivars. Alm1 A genomic RNA accumulated similarly in the three cultivars, whereas the accumulation of Jor genomic RNA was lower in the resistant cultivars than in the susceptible cultivar. Also the Jor isolate and accumulated earlier and at a higher level than the Alm 1A isolate in the three cultivars.

Histochemical Studies of the Non‐Host Resistance and the Role of Actin Cytoskeleton in Pepper Against Colletotrichum orbiculare

AbstractThe penetration process and defence reactions (hypersensitive response, oxidative burst and cell wall fortification) of Colletotrichum orbiculare were studied histochemically on pepper cultivar ‘A11’ (non‐host) and susceptible cucumber cultivar ‘Changchun Thorn’ (host). The results indicate that C. orbiculare could hardly penetrate the non‐host pepper leaves. It was papillae rather than hypersensitive response and H2O2 that played an important role in resisting the colonization and development of C. orbiculare on the non‐host pepper. The depolymerization of the actin microfilament weakened the papilla deposition of pepper and allowed successful penetration of the non‐adapted C. orbiculare, suggesting that the actin cytoskeleton of pepper is significant in preventing the invasion of the non‐host pathogen C. orbiculare.

Self-inhibition of spore germination via reactive oxygen in the fungus Cladosporium cucumerinum, causal agent of cucurbit scab

Cladosporium cucumerinum spore germination in vitro depended on spore suspension density. Different fungal isolates displayed germination maxima at different spore concentrations. For one isolate, the maximum was observed at the same spore density at both 18 and 25°C, although germination percentage increased slightly at the higher temperature. Diffusates originating in other spore suspensions of the same isolate reduced germination percentage of spores taken at optimal concentration. The least effect occurred in diffusate taken from spores kept at their optimal concentration. Self-suppression of spore germination at unfavourable concentrations was diminished more or less by antioxidants (superoxide dismutase, catalase, mannitol or formate). The same compounds, added to spore diffusates, reduced their fungitoxicities. All diffusates generated superoxide radical (assayed by adrenalin oxidation sensitive to superoxide dismutase). This activity correlated positively with diffusate toxicity. Leaf inoculation of the susceptible cucumber cultivar at 18°C with spore suspensions at extreme densities, at which they germinated poorly in vitro, led to less disease severity then that at optimal density. In contrast, no disease symptoms appeared at 25°C. It is suggested that spores germinating at their extreme concentrations produced reactive oxygen species, suppressing the pathogen; this effect could reduce disease development at low temperatures. At high temperatures, however, this mechanism seems not to work, suggesting that plant infection may be reduced by other disease inhibiting factors.