Cucumber Fusarium Wilt Research Articles

Formulations can affect rhizosphere colonization and biocontrol efficiency of Trichoderma harzianum SQR-T037 against Fusarium wilt of cucumbers

Pot experiments were carried out over two growing periods to assay the biocontrol efficacy and rhizosphere colonization of Trichoderma harzianum SQR-T037 (SQR-T037) applied as SQR-T037 conidia suspension (TCS), SQR-T037 conidia suspension blended with organic fertilizer (TBF), or SQR-T037 fermented organic fertilizer (TFF). Each formulation had three T. harzianum numbers. In two experiments, Percent Disease Indexes (PDIs) decreased with the increase of SQR-T037 number added to soils. The TFF treatment consistently exhibited the lowest PDIs at same amendment rate of SQR-T037 and 0–8.9%, 25.6–78.9%, and 4.4–50.0% of PDIs were found in TFF, TCS, and TBF treatment, respectively. Soils treated with TFF showed the highest SQR-T037 population in rhizosphere and bulk soil. Decrease of Fusarium oxysporum population in both bulk and rhizosphere soils occurred in the treatment SQR-T037 at 105 and 106 cfug−1 soil rate. The TFF treatment at the SQR-T037 rate of 103 cfug−1 soil significantly (p < 0.05) increased SQR-T037 population within the rhizoplane but had no effect on F. oxysporum population when compared to TCS and TBF. Generally, TFF treatments were superior to TCS and TBF treatments on disease control by sustaining colonization of SQR-T037 and decreasing F. oxysporum abundance in the rhizosphere soil. We propose that TFF treatment at SQR-T037 rate of 107 cfug−1 (i.e., 105 cfug−1 soil after applied to soil) was the best formulation for controlling Fusarium wilt of cucumber.

Solid-state fermentation of agro-industrial wastes to produce bioorganic fertilizer for the biocontrol of Fusarium wilt of cucumber in continuously cropped soil

Agro-industrial wastes of cattle dung, vinegar-production residue and rice straw were solid-state fermented by inoculation with Trichoderma harzianum SQR-T037 (SQR-T037) for production of bioorganic fertilizers containing SQR-T037 and 6-pentyl-α-pyrone (6PAP) to control Fusarium wilt of cucumber in a continuously cropped soil. Fermentation days, temperature, inoculum and vinegar-production residue demonstrated significant effects on the SQR-T037 biomass and the yield of 6PAP, based on fractional factorial design. Three optimum conditions for producing the maximum SQR-T037 biomass and 6PAP yield were predicted by central composite design and validated. Bioorganic fertilizer containing 8.46log10 ITS copies g−1 dry weight of SQR-T037 and 1291.73mgkg−1 dry weight of 6PAP, and having the highest (p<0.05) biocontrol efficacy, was achieved at 36.7 fermentation days, 25.9°C temperature, 7.6% inoculum content, 41.0% vinegar-production residue, 20.0% rice straw and 39.0% cattle dung. This is a way to offer a high value-added use for agro-industrial wastes.

Arbuscular Mycorrhizal Fungal Inoculation Enhances Suppression of Cucumber Fusarium Wilt in Greenhouse Soils

A pot experiment was conducted to study the plant growth and fruit yields of cucumber ( Cucumis sativus L.) on a greenhouse soil with or without inoculation of arbuscular mycorrhizal fungi (AMFs) and Fusarium oxysporum f. sp. cucu-merinum under unsterilized conditions. Two AMF inocula were tested: only one AMF strain Glomus caledonium 90036 and an AMF consortium mainly consisting of Glomus spp. and Acaulospora spp. There were four treatments including no inoculation (control), inoculation with F. oxysporum but without mycorrhizae (FO), inoculation with F. oxysporum and G. caledonium (FO+M1), and inoculation with F. oxysporum and the AMF consortium (FO+M2). Cucumber plants were harvested at weeks 3 and 9 after transplanting. Compared with the control, the FO treatment without AMF inoculation had less biomass both at weeks 3 and 9 ( P < 0.05) and had higher incidence of Fusarium wilt and produced no cucumber fruit at week 9. Both FO+M1 and FO+M2 treatments had higher mycorrhizal colonization than the treatments which received no AMF inoculation at week 3 ( P < 0.05), but only the FO+M2 treatment elevated plant biomass, decreased the incidence of Fusarium wilt, and improved cucumber yields to the same level as the control at week 9. The results indicated that the AMF consortium could suppress Fusarium wilt of cucumber and, therefore, showed potential as a biological control agent in greenhouse agroecosystems.

Soil microbial community structure in cucumber rhizosphere of different resistance cultivars to fusarium wilt

Cucumber fusarium wilt is a common soil-borne disease. We hypothesize that there is a relationship between the severity of disease and soil microbial ecology. In this work, culturable microbial populations, lipid fatty acid and community-level physiological profiles (CLPP) from rhizosphere soils of four different cucumber cultivars were investigated. Comparatively higher actinomycetes, mycorrhizal colonization and higher ratios of bacteria to fungi were found in the two resistant cultivars compared with the two susceptible cultivars. CLPP analysis showed that catabolic diversity indices were higher in the presence of two resistant cultivars. Phospholipid fatty acid (PLFA) profiles suggested that fungal (18:2omega6,9c) PLFA was enriched in the rhizosphere soils of the two susceptible cultivars, but some bacterial (16:0 and 15:0a) PLFAs were found in a lower relative abundance in these soils. The neutral lipid fatty acid 16:1omega5, which is an indicator of arbuscular mycorrhizal fungi, was enriched in the rhizosphere soils of the two resistant cultivars. All the three methods suggested that plant genotype had a significant impact on the soil microbial community composition and activity, and the differences in the rhizosphere microbial community may result in the differences in the resistance to fusarium wilt.

Quantitative changes of plant defense enzymes and phytohormone in biocontrol of cucumber Fusarium wilt by Bacillus subtilis B579

Fusarium oxysporum f. sp. cucumerinum is a destructive pathogen on cucumber (Cucumis sativus L.) seedlings and the causal organism of crown and root rot of cucumber plants. An isolate of B579, which was identified as Bacillus subtilis by 16S rDNA sequences analysis, was selected from 158 bacteria isolates as the best antagonist against F. oxysporum by dual plate assay. The production of chitinase, β-1, 3-glucanase, siderophores, indole-3-acetic acid (IAA), hydrogen cyanide (HCN), and phosphate solubilization, by B579 were screened with the selected medium by in vitro tests. The cell-free culture filtrate of B579, with a concentration of 20% (v/v), could result in the vacuolation, swelling and lysis of hyphae. Besides, it could blacken, shrunk and hindered the germination of conidia of F. oxysporum at the concentration of ≥80% (v/v). When applied as inoculants, B579 (108 c.f.u. ml−1) was able to reduce disease incidence by 73.60%, and promote seedling growth in pot trial studies. The activities of plant defense-related enzyme, peroxidase (POX), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) were significantly increased in plants treated with B579. Interestingly, a higher content of IAA, an important plant growth regulator, was detected in B579 treated plants. Furthermore, seed-soaking with B579 exhibited a better biological control effect (Biocontrol effect 73.60%) and plant growth promoting ability (Vigor Index 4,177.53) than root-irrigation (50.88% and 3,575.77, respectively), suggesting the potential use of B579 as a seed-coating agent.

Differentially expressed transcripts from cucumber ( Cucumis sativus L.) root upon inoculation with Fusarium oxysporum f. sp. cucumerinum Owen

Fusarium wilt of cucumber is a serious vascular disease worldwide. The molecular interaction between cucumber ( Cucumis sativus L.) and Fusarium oxysporum was investigated by construction and characterization of a suppression subtractive hybridization cDNA library, which was constructed from F. oxysporum-inoculated cucumber. To screen the differentially expressed genes, dot blotting was used with cDNA probes prepared from mRNAs of control and F. oxysporum-inoculated samples. The elevated expression levels and overall profiles over time of eight genes were conformed by semi-quantitative RT-PCR analysis. Acquired positive clones were subjected to sequence and homology search analysis. In total, 153 ESTs were acquired after screening. Among these 153 ESTs, 80 ESTs showed significant sequence similarity to known genes, 51 had unknown functions, 22 clones did not match any known sequences. Most of the ESTs with known functions were involved in defense response, metabolism and transcriptional regulation. So upon F. oxysporum inoculation, cucumber could express defense-related genes as well as enhance its metabolic activities. The most interesting finding was that several genes were related to ABA, suggesting ABA singling may play a positive role in defense mechanism in cucumber to F. oxysporum. Our study provides an overview of gene expression in F. oxysporum-inoculated cucumber, as well as useful information of the defense mechanism in plant to necrotrophic fungi pathogens.

A CBR method for CFW prevention and treatment

Different from the conventional methods, this paper presents a case-based reasoning (CBR) method for cucumber fusarium wilt (CFW) prevention and treatment, with vantage case-based indexing and retrieval mechanism, sensitivity analysis based reasoning method and Recall evaluation based case retaining strategy. The optimal interval of case dissimilarity distance threshold T is inferred from the experimental results by X fold cross-validation method. The experiments and application show that useful information can be generated for CFW prevention and treatment and the dynamic adjustment for decision-making of cucumber planting can be assisted by the proposed CBR system.

Land use intensification affects soil microbial populations, functional diversity and related suppressiveness of cucumber Fusarium wilt in China’s Yangtze River Delta

The extent of soil microbial diversity in agricultural soils is critical to the maintenance of soil health and quality. The aim of this study was to investigate the influence of land use intensification on soil microbial diversity and thus the level of soil suppressiveness of cucumber Fusarium wilt. We examined three typical microbial populations, Bacillus spp., Pseudomonas spp. and Fuasarium oxysporum, and bacterial functional diversity in soils from three different land use types in China’s Yangtze River Delta, and related those to suppressiveness of cucumber Fusarium wilt. The land use types were a traditional rice wheat (or rape) rotation land, an open field vegetable land, and a polytunnel greenhouse vegetable land that had been transformed from the above two land use types since 1995. Results generated from the field soils showed similar counts for Bacillus spp. (log 5.87–6.01 CFU g−1 dw soil) among the three soils of different land use types, significantly lower counts for Pseudomonas spp. (log 5.44 CFU g−1 dw soil) in the polytunnel greenhouse vegetable land whilst significantly lower counts for Fusarium oxysporum (log 3.21 CFU g−1 dw soil) in the traditional rice wheat (or rape) rotation land. A significant lower dehydrogenase activity (33.56 mg TPF kg−1 dw day−1) was observed in the polytunnel greenhouse vegetable land. Community level physiological profiles (CLPP) of the bacterial communities in soils showed that the average well color development (AWCD) and three functional diversity indices of Shannon index (H′), Simpson index (D) and McIntosh index (U) at 96 h incubation in BIOLOG Eco Micro plates were significantly lower in the polytunnel greenhouse vegetable land than in both the traditional rice wheat (or rape) rotation land and the open field vegetable land. A further greenhouse experiment with the air-dried and sieved soils displayed significantly lower plant growth parameters of 10-old cucumber seedlings as well as significantly lower biomass and total fresh fruit yield at the end of harvesting at day 70 in the polytunnel greenhouse vegetable soil sources. The percentages of Fusarium wilt plant death were greatly increased in the polytunnel greenhouse vegetable plants, irrespective of being inoculated with or without Fusarium oxysporum f. sp. cucumerinum. Our results could provide a better understanding of the effects of land use intensification on soil microbial population and functional diversity as well as the level of soil suppressiveness of cucumber Fusarium wilt.

Influence of plant root exudates, germ tube orientation and passive conidia transport on biological control of fusarium wilt by strains of nonpathogenic Fusarium oxysporum.

In earlier studies, biological control of Fusarium wilt of cucumber induced by Fusarium oxysporum f. sp. cucumerinum was demonstrated using nonpathogenic strains C5 and C14 of Fusarium oxysporum. Strain C14 induced resistance and competed for infection sites whether roots were wounded or intact, whereas strain C5 required wounds to achieve biocontrol. In the current work, additional attributes involved in enhanced resistance by nonpathogenic biocontrol agents strains to Fusarium wilt of cucumber and pea were further investigated. In pre-penetration assays, pathogenic formae specials exhibited a significantly higher percentage of spore germination in 4-day-old root exudates of cucumber and pea than nonpathogens. Also, strain C5 exhibited the lowest significant reduction in spore germination in contrast to strain C14 or control. One-day-old cucumber roots injected with strain C14 resulted in significant reduction in germ tube orientation towards the root surface, 48-96 h after inoculation with F. o. cucumerinum spores, whereas strain C5 induced significantly lower spore orientation of the pathogen and only at 72 and 96 h after inoculation. In post-penetration tests, passive transport of microconidia of pathogenic and nonpathogens in stems from base to apex were examined when severed plant roots were immersed in spore suspension. In repeated trials, strain C5, F. o. cucumerinum and F. o. pisi were consistently isolated from stem tissues of both cucumber and pea at increasing heights over a 17 days incubation period. Strain C14 however, was recovered at a maximum translocation distance of 4.6 cm at day 6 and later height of isolation significantly declined thereafter to 1.2 cm at day 17. In pea stem, the decline was even less. Significant induction of resistance to challenge inoculation by the pathogen in cucumber occurred 72 and 96 h after pre-inoculation with biocontrol agents. Nonetheless, strain C14 induced protection as early as 48 h and the maximum resistance was reached at 96 h. The presented data confirm the previous findings that attributes important for nonpathogenic fusaria to induce resistant are: rapid spore germination and orientation in response to root exudate; active root penetration and passive conidia transport in stem to initiate defence reaction without pathogenicity and enough lag period between induction and challenge inoculation. Strain C14 possesses all these qualifications and hence its ability to enhance host resistance is superior than strain C5.

Cinnamic acid causes oxidative stress in cucumber roots, and promotes incidence of Fusarium wilt

To ascertain whether oxidative stress plays a role in promoting the incidence of Fusarium wilt of cucumber, the activities of several antioxidant enzymes, namely superoxide dismutase (SOD), guaiacol-dependent peroxidase (GPX), ascorbate peroxidase (APX) and catalase (CAT) together with contents of H 2O 2, MDA and O 2 − , were determined in cucumber root after exposure to cinnamic acid and prior to the inoculation of Fusarium oxysporum (Schlechtend,:Fr) f. sp. cucumerinum. Results showed that plant growth was greatly inhibited by cinnamic acid at 0.05–0.25 mM, accompanied by a higher incidence of Fusarium wilt. Effects increased with the concentration of cinnamic acid. The increase in SOD, APX, CAT and GPX activities as well as the H 2O 2 and O 2 − contents became increasingly apparent with increasing concentration of cinnamic acid. Exposure to cinnamic acid resulted in enhanced membrane peroxidation and decreased plasma membrane H +-ATPase, vacuolar H +-ATPase and PPase activities. Moreover, it also increased the activities of phenylalanine ammonia-lyase and polyphenolase together with increased levels of phenolics and flavonoids. It is likely that the enhanced incidence of Fusarium wilt is associated with oxidative stress triggered by cinnamic acid.

Incidence of Fusarium wilt in Cucumis sativus L. is promoted by cinnamic acid, an autotoxin in root exudates

The effects of Fusarium oxysporum f. sp. cucumerinum, the pathogen causing Fusarium wilt in cucumber and cinnamic acid, a principal autotoxic component in the root exudates of cucumber (Cucumis sativus L.), on plant growth, Photosynthesis and incidence of Fusarium wilt in cucumber were studied in order to elucidate the interaction of autotoxins and soil-borne pathogens in the soil sickness. F. oxysporum. f. sp. cucumerinum (FO) and cinnamic acid (CA) at 0.1 or 0.25 mM significantly decreased net photosynthetic rate, stomatal conductance and the quantum yield of Photosystem II photochemistry (ΦPSII), followed by a reduction of plant biomass production, but did not induce photoinhibition. Pretreatment with CA before inoculation with FO increased the effectiveness of FO, together with a slight photoinhibition. CA pretreatment significantly increased percentage of plants affected by Fusarium wilt, browning index of vascular bundle and Fusarium population in the nutrient solution. All these results indicate that CA enhanced Fusarium wilt by predisposing cucumber roots to infection by FO through a direct biochemical and physiological effect. It is likely that soil sickness results from an interaction of many factors. Abbreviations: CA – cinnamic acid; CFU – colony forming units; Ci – intercellular CO2 concentration; FO –Fusarium oxysporum (Schlechtend.:Fr) f. sp. cucumerinum (Owen) Snyder & Hansen; Fv/Fm– maximal quantum efficiency of PS II; Fv′/Fm′– the efficiency of excitation capture by open PS II centers; Gs – stomatal conductance; NPQ – non-photochemical quenching coefficient; Pn – net photosynthetic rate; PS II – Photosystem II; ΦPS II– the quantum yield of PS II photochemistry; qP – photochemical quenching coefficient.

Response of transgenic cucumber expressing a rice class I chitinase gene to two fungal pathogens with different infectivities

A transgenic cucumber line (CR32) over-expressing the rice class I chitinase gene exhibited resistance to Phytophthora rot (Phytophthora nicotianae var. parasitica) but not to Fusarium wilt (Fusarium oxysporum f. sp. cucumerinum). The infection behavior of these fungi on CR32 and nontransgenic plants was examined with an optical microscope. In zoosporangia of P. nicotianae var. parasitica, the rates of germination and penetration on leaves of both CR32 and nontransgenic plants were almost equal. After infection, however, the growth of infection hyphae was markedly suppressed in CR32 compared with their growth in the nontransgenic plants. In F. oxysporum f. sp. cucumerinum, the infection hyphae localized in petiole vessels of both CR32 and nontransgenic plants, and growth did not differ in the two plants. We investigated the antifungal activity of a high-molecular-weight fraction (HF) and a low-molecular-weight fraction (LF) of crude leaf extracts from CR32 and from the nontransgenic line. CR32 HF, which included the rice chitinase, had antifungal activity only against F. oxysporum f. sp. cucumerinum. In contrast, CR32 LF, which did not have the rice chitinase, had strong antifungal activity against the two fungi. These results suggested that a low-molecular-weight antifungal substance(s) was induced in CR32 and might function as a factor of resistance to P. nicotianae var. parasitica, which has cell walls that almost never contain chitin. Because rice chitinase has already been demonstrated not to localize in vessels of CR32, the infection localization of F. oxysporum f. sp. cucumerinum in vessels might enable the fungus to avoid antifungal substance(s), resulting in Fusarium wilt in transgenic cucumber.

Effects of cultivation of preceding plants on the development of Fusarium wilt of cucumber and daikon

The effects of the cultivation of preceding plants on the inhibition of Fusarium wilts, vessel diseases of cucumber (Cucumis sativus) caused by Fusarium oxysporum f. sp. cucumerinum (FOC) and yellows of daikon (Raphanus sativus var. longipinnatus) caused by F. oxysporum f. sp. raphani (FOR), were examined. When the cucumber or daikon plant was cultivated as a succeeding plant in the pots where the soils had been inoculated with a spore suspension of FOe or FOR and then various preceding plants had been cultivated, the percentage of disease of the succeeding plants was lower in some plots than in the control plot without preceding plants. Spinach (Spinacia oleracea, cv. Atlas) and burdock (Arctium lappa, cv. Takinogawa) inhibited significantly the vessel disease caused by FOe. Thrnip (Brassica rapa, Parental Line Nou No.1) and spinach (S. oleracea, cv. Try) suppressed the yellows caused by FOR. When the number of FOC or FOR was estimated by the recovery using Komada med.ium and by testing their pathogenicity to the host plant, cucumber or daikon, the numbers of both were not reduced in the plots even where these plants had been cultivated initially. The soil extract from the pots, where preceding plants had been cultivated, did not affect the conidia of FOC and FOR. In both FOC and FOR experiments, the cultivation of preceding plants increased the number of bacteria in soil. Additionally, in the FOR experiment, preceding plants, turnip and spinach, increased the number of F. oxysporum (FOX) except for FOR and decreased the proportion of FOR to FOX. It was suggested that these preceding plants might affect the pathogens of Fusarium wilt indirectly by the changes in the numbers and flora of soil microorganisms.

Use of Quantitative Models to Describe the Efficacy of Inundative Biological Control of Fusarium Wilt of Cucumber

Fusarium wilt of cucumber caused by Fusarium oxy-sporum f. sp. cucumerinum is a serious vascular disease worldwide. Biological control of Fusarium wilt in several crops has been accomplished by introducing non-pathogenic Fusarium sup. and other biocontrol agents in soil or in infection courts. In this study, quantitative models were used to determine the biocontrol efficacy of inundatively applied antagonist formulations and the length of their effectiveness in controlling Fusarium wilt of cucumber. Quantitative model of the form [Y=L (1<TEX>${-exp}^{-kx}$</TEX>)] best described the relationship between disease incidence (Y, %) and inoculum density (X) of isolates F51 and F55. Isolate F51 was selected as a more virulent isolate based on the extent of its effectiveness in causing the wilt disease. The degree of disease control (Xi/X) obtained with the density of the biocontrol agent (Z), was described by the model [Xi/X=A (1<TEX>${-exp}^{-cz}$</TEX>)]. The zeolite-based antagonist formulation amended with chitosan (ZAC) was better at lower rates of application and peaked at around 5 g/ kg of the potting medium, whereas the peat-based antagonist formulation (PA) peaked at around 10 g/kg of the potting medium. ZAC formulation provided significantly better suppression of Fusarium wilt as described by the curvilinear relationship of the type Y= a+bX+c<TEX>$X^2$</TEX>, where Y represents percent disease incidence and X represents sustaining effect of the biocontrol agent.

First report of fusarium wilt of cucumber caused by Fusarium oxysporum in Spain

First report of fusarium wilt of cucumber caused by <i>Fusarium oxysporum</i> in Spain

Biological Control of Fusarium Wilt of Cucumber by Chitinolytic Bacteria

ABSTRACT Two chitinolytic bacterial strains, Paenibacillus sp. 300 and Streptomyces sp. 385, suppressed Fusarium wilt of cucumber (Cucumis sativus) caused by Fusarium oxysporum f. sp. cucumerinum in nonsterile, soilless potting medium. A mixture of the two strains in a ratio of 1:1 or 4:1 gave significantly (P < 0.05) better control of the disease than each of the strains used individually or than mixtures in other ratios. Several formulations were tested, and a zeolite-based, chitosan-amended formulation (ZAC) provided the best protection against the disease. Dose-response studies indicated that the threshold dose of 6 g of formulation per kilogram of potting medium was required for significant (P < 0.001) suppression of the disease. This dose was optimum for maintaining high rhizosphere population densities of chitinolytic bacteria (log 8.1 to log 9.3 CFU/g dry weight of potting medium), which were required for the control of Fusarium wilt. The ZAC formulation was suppressive when added to pathogen-infested medium 15 days before planting cucumber seeds. The formulation also provided good control when stored for 6 months at room temperature or at 4 degrees C. Chitinase and beta-1,3-glucanase enzymes were produced when the strains were grown in the presence of colloidal chitin as the sole carbon source. Partial purification of the chitinases, followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and activity staining, revealed the presence of five bands with molecular masses of 65, 62, 59, 55, and 52 kDa in the case of Paenibacillus sp. 300; and three bands with molecular masses of 52, 38, and 33 kDa in the case of Streptomyces sp. 385. Incubation of cell walls of F. oxysporum f. sp. cucumerinum with partially purified enzyme fractions led to the release of N-acetyl-D-glucosamine (NAGA). NAGA content was considerably greater when pooled enzyme fractions (64 to 67) from Paenibacillus sp. were used, because they contained high beta-1,3-glucanase activity in addition to chitinase activity. Suppression of Fusarium wilt of cucumber by a combination of these two bacteria may involve the action of these hydrolytic enzymes.

Induced resistance of acibenzolar-S-methyl (CGA 245704) to cucumber and Japanese pear diseases.

Antifungal activity of the novel compound acibenzolar-S-methyl (CGA245704: benzo[1,2,3]thiadiazole-7-carbothioic acid S-methyl ester) was examined in vitro. No remarkable activity was observed on mycelial growth and conidial germination of almost all fungi tested. Only melon isolates of Didymella bryoniae were sensitive to this compound. On potted plants, acibenzolar-S-methyl showed control efficacy on anthracnose and scab of cucumber and rust of Japanese pear but not on Fusarium wilt of cucumber. In field trials, the occurrence of both rust and scab on Japanese pear was suppressed with this compound. Based on these experiments, it was suggested that acibenzolar-S-methyl induced resistance to some but not all diseases on cucumber and Japanese pear. Induction of disease resistance in cucumber was rapidly triggered after treatment with acibenzolar-S-methyl.

Allelism of theFcu-1 andFoc genes conferring resistance to fusarium wilt in cucumber

The inheritance of resistance toFusarium oxysporum f.sp.cucumerinum race 1 was determined in the cucumber cv. WIS-248 by analyzing segregation of F1, F2, and BC populations of crosses with the susceptible cv. Straight-8. Resistance was conferred by a single dominant gene. In an allelism test, it was proven that theFcu-1 gene, which confers resistance toF. oxysporum f.sp.cucumerinum races 1 and 2 in cucumber cv. SMR-18 and theFoc gene, which confers resistance toF. oxysporum f.sp.cucumerinum race 2 in cucumber cv. WIS-248, are indistinguishable.

Screening of melon (Cucumis melo L.) germplasm for multiple disease resistance

Melon germplasm was screened for cucumber green mottle mosaic virus (CGMMV), powdery mildew (Sphaerotheca fuliginea), downy mildew (Pseudoperonospora cubensis) and Fusarium wilt (Fusarium oxysporum f. sp. melonis) resistance under artificial conditions except downy mildew for which screening was done under natural epiphytotic conditions. High level resistance to all the four diseases was not recorded in any of the collections tested. Nevertheless, ertheless, resistance to three diseases was located in three germplasm. Wild Cucumis species C. figarei exhibited absolute resistance to CGMMV and Fusarium wilt and high level resistance to downy mildew. Phoot or snapmelon (Cucumis melo var. momordica) — a non-dessert from of Indian origin—was highly resistant to downy mildew and resistant to CGMMV and medium resistant to Fusarium wilt. Iroquois was resistant to powdery mildew and medium resistant to downy mildew and CGMMV.

Ecology of Plant Pathogenic Fusarium spp. in Soil and Prevention of Cucumber Fusarium Wilt by Cultural Practices

Ecology of Plant Pathogenic <i>Fusarium</i> spp. in Soil and Prevention of Cucumber Fusarium Wilt by Cultural Practices