Fusarium Wilt Of Watermelon Research Articles

A Genetic Locus Associated with Resistance to Fusarium oxysporum f. sp. niveum Race 2 in Citrullus lanatus-type Watermelon

Fusarium wilt of watermelon (Citrullus lanatus), caused by Fusarium oxysporum f. sp. niveum (FON), is a devastating soil-borne disease limiting watermelon production across the world. Although many watermelon cultivars have been bred for resistance to FON races 0 and 1, the only released cultivars that are resistant to FON 2 are nonharvested pollenizers. The lack of FON 2–resistant edible cultivars is thought to be associated with linkage drag and/or preferential inheritance patterns observed when crossing the resistant, wild source (Citrullus amarus), with edible watermelon. A potential way to overcome these obstacles is to use a resistant C. lanatus as the source of resistance and to develop molecular markers to increase the efficiency of selection. Here we describe the identification of a quantitative trait locus (QTL) associated with FON 2 resistance in watermelon. The genotyping by sequencing (GBS) platform was used to generate single nucleotide polymorphisms (SNPs) in an F2 population (n = 178) developed from a cross between UGA147 (resistant) and ‘Charleston Gray’ (susceptible). Five hundred and one SNPs were placed on the watermelon physical map and used in the mapping of QTL. F3 lines were phenotyped for resistance to FON 2 in the greenhouse. An intermediate QTL associated with resistance to FON 2 was identified on chromosome 11 (Qfon11). This QTL is a potential target for marker-assisted selection (MAS) for FON 2 resistance in watermelon.

Factors Associated with Leguminous Green Manure Incorporation and Fusarium Wilt Suppression in Watermelon.

Fall-planted Vicia villosa or Trifolium incarnatum cover crops, incorporated in spring as a green manure, can suppress Fusarium wilt (Fusarium oxysporum f. sp. niveum) of watermelon. During cover crop growth, termination, and incorporation into the soil, many factors such as arbuscular mycorrhizae colonization, leachate, and soil respiration differ. How these cover-crop-associated factors affect Fusarium wilt suppression is not fully understood. Experiments were conducted to evaluate how leachate, soil respiration, and other green-manure-associated changes affected Fusarium wilt suppression, and to evaluate the efficacy of the biocontrol product Actinovate AG (Streptomyces lydicus WYEC 108). General and specific suppression was examined in the field by assessing the effects of cover crop green manures (V. villosa, T. incarnatum, Secale cereale, and Brassica juncea) on soil respiration, presence of F. oxysporum spp., and arbuscular mycorrhizal colonization of watermelon. Cover crop treatments V. villosa, T. incarnatum, and S. cereale and no cover crop were evaluated both alone and in combination with Actinovate AG in the greenhouse. Additionally, in vitro experiments were conducted to measure the effects of cover crop leachate on the mycelial growth rates of F. oxysporum f. sp. niveum race 1 and Trichoderma harzianum. Soil microbial respiration was significantly elevated in V. villosa and Trifolium incarnatum treatments both preceding and following green manure incorporation, and was significantly negatively correlated with Fusarium wilt, suggesting that microbial activity was higher under the legumes, indicative of general suppression. Parallel to this, in vitro growth rates of F. oxysporum f. sp. niveum and Trichoderma harzianum on V. villosa leachate amended media were 66 and 213% greater, respectively, than on nonamended plates. The F. oxysporum spp. population (based on CFU and not differentiated into formae specialis or races) significantly increased in V. villosa-amended field plots. Additionally, the percentage of watermelon roots colonized by arbuscular mycorrhizae following V. villosa and Trifolium incarnatum green manures was significantly higher than in watermelon following bare ground (58 and 44% higher, respectively). In greenhouse trials where cover crops were amended to soil, Actinovate AG did not consistently reduce Fusarium wilt. Both general and specific disease suppression play a role in reducing Fusarium wilt on watermelon.

Exploiting Illumina sequencing for the development of InDel markers in watermelon (Citrullus lanatus)

ABSTRACTWatermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] is a cross-pollinating diploid species and is one of the most important dicotyledonous plants belonging to the family Cucurbitaceae due to its high nutritional value, rapid growth, sweet and juicy taste, and refreshing nature as a summer fruit. However, the insertion–deletion (InDel) markers available for watermelon cannot satisfy the demand to identify and map resistance genes in this major crop. In this study, we have characterised and developed numerous polymorphic InDel markers using Illumina re-sequencing of a male parental line that is resistant to Fusarium wilt. In total, 25,701 potential InDel markers were identified, with a mean size of 18 bp. From these, 7,387 potential InDel markers > 10 bp were selected and tested as candidate InDel markers to locate resistance genes for map-based cloning and polymorphism analysis. We designed and synthesised 69 primer pairs using Primer 3 software. Overall, 54 primer pairs detected polymorphism between the Fusarium-susceptible female parent ‘JSw01-1’ and the Fusarium-resistant male parent ‘JRw08-3’. Among the 69 InDel markers, 54 (78.3%) exhibited polymorphism at 179 PCR loci. Polymorphic information content (PIC) values ranged from 0.04 to 0.91, and the number of alleles per primer ranged from 1 to 11. The 54 InDel markers that were mined and exploited via Illumina re-sequencing of watermelon could accelerate the development of marker-assisted breeding and the progression of genetic research to understand resistance to Fusarium wilt in watermelon.

Induction of Resistance in Watermelon Plants against Fusarium Wilt using Chemical Inducers and Compost under Greenhouse Conditions

Fusarium wilt of watermelon caused by Fusarium oxysporum f.sp. niveum is the most severe disease attacking watermelon plants. Induced resistance in watermelon plants using chitosan, salicylic acid and compost was evaluated. All tested isolates of F. oxysporum f.sp. niveum were able to attack watermelon plants causing damping-off symptoms. The most aggressive isolate was isolated from Nobariya (cv. Giza 1). It caused 71.9, 46.9 and 51.6% damping-off for cvs. Gorma, Giza1 and Aswan hybrid, respectively, 30 days after sowing. Laboratory experiment results revealed that all tested concentrations of chitosan and salicylic acid significantly reduced the disease incidence under greenhouse conditions. Moreover, animal and plant compost at all concentrations significantly reduced the watermelon wilt incidence. Plant compost at 10.0 g/kg soil, chitosan at 8.0 g/kg soil and salicylic acid at 2.0 g/kg soil were tested alone or in combination to study their effect on watermelon wilt incidence and on enzyme activities of watermelon plants. Results showed that the highest reduction in disease incidence was recorded with combined treatments between plant compost and chitosan at concentration of 8.0 g/kg soil or salicylic acid at 2.0 g/kg soil which reduced the dead plant (%) by 92.9, 88.5 and 86.6% for Aswan hybrid, cvs. Gorma and Giza1, respectively. As for enzyme activities, results revealed that the highest increase was recorded with combined treatments between plant compost and chitosan at concentration of 8 g/kg soil or salicylic acid at 2.0 g/kg soil which increased the peroxidase, chitinase and β-1,3-glucanase activities.

Characterization of the watermelon seedling infection process by Fusarium oxysporum f. sp. niveum

Fusarium oxysporum f. sp. niveum (FON) is the causal pathogen of fusarium wilt in watermelon. Understanding the interactions of watermelon seedlings and FON is of scientific and practical importance for disease control. The colonization dynamics of a susceptible watermelon cultivar, Sumi 1 (SM 1), were visualized using a green fluorescent protein (GFP)‐expressing strain of FON race 1 (FON 1‐GFP). Within 2 days post‐inoculation (dpi), hyphae adhered to and grew on epidermal cells. At 3 dpi, hyphae crossed the epidermis, penetrated into the cortex and progressed through parenchymal cell borders reaching the xylem vessels at 7 dpi. Growth of hyphae was restricted to the xylem vessels even in the colonized lower hypocotyl. The responses of SM 1 seedlings to infection were analysed. In the roots of SM 1, infected xylem vessels were plugged with gums and tyloses and some occluded vessels were shed from the root vascular tissue. Parenchyma cells surrounding the vascular cylinder showed wall thickening and cell disintegration, which eventually formed cavities. Hypocotyls of most SM 1 plants were also infected. Vascular tissues were densely colonized by hyphae until the vascular bundle became hollow and plants withered. Moreover, the expression patterns of six defence‐related genes in roots of SM 1 were analysed using real‐time quantitative PCR. Transcript levels of plant defensin‐like genes ClPDF2.1 and ClPDF2.4, phenylalanine ammonia lyase (PAL), chitinase (CHI) and ascorbate peroxidase (APX) were significantly induced in SM 1 roots during FON 1 infection, while polyphenoloxidase (PPO) did not show significant responses to FON 1 infection.

Companion cropping with wheat increases resistance to Fusarium wilt in watermelon and the roles of root exudates in watermelon root growth

Pot experiments were performed to investigate the effects of companion cropping with D125 wheat on Fusarium wilt in watermelon. Fusarium oxysporum f. sp. niveum (Fon) is responsible for Fusarium wilt in watermelon. Also, the relationship between root exudates of wheat and watermelon growth was estimated. Studies showed that companion cropping with D125 wheat reduced the incidence rate of watermelon Fusarium wilt. Companion cropping with D125 wheat decreased malondialdehyde content and increased activities of phenylalanine ammonia-lyase and polyphenol oxidase and contents of flavonoid, total soluble phenolics and lignin in watermelon roots after inoculation with Fon compared to monoculture. qRT-PCR showed that the expression levels of six specific genes were higher during the early stage of Fon infection in companion cropping than in monoculture. D125 wheat root exudates increased root length, root surface area, root volume, root number, root dry weight, but decreased root mean diameter in watermelon seedlings in the absence of sodium orthovanadate. These results suggest that companion cropping with D125 wheat reduced Fusarium wilt in watermelon by promoting the growth of watermelon roots and by triggering gene expression and physiological changes to protect the watermelon from injury.

Evaluation of the biocontrol potential of Streptomyces goshikiensis YCXU against Fusarium oxysporum f. sp. niveum

A rhizobacterium with broad spectrum antifungal activity was isolated from the rhizosphere of a healthy cucumber plant in a Fusarium wilt diseased field. Phylogenetic tree analysis based on similarity percentage showed that the bacterium was 99% affiliated with the species Streptomyces goshikiensis. The strain, coded as S. goshikiensis YCXU, inhibited in vitro a broad range of phytopathogenic fungi, so it was selected for more detailed characterization. The strain could utilize different carbon sources and exhibited catalase, β-1,3-glucanase, chitinase and urease enzyme activities. The strain showed maximum growth at the pH of 7, temperature of 28°C and NaCl concentration of 1%. The stain was able to produce antifungal diffusible and volatile organic compounds that significantly inhibited the growth of pathogenic fungi. In the greenhouse experiments, watermelon plants fresh and dry weights were significantly increased, and the incidence of Fusarium wilt was decreased by 67% when the strain enriched by a bioorganic fertilizer was applied to both nursery soil and pot soil (NS). The treatment NS also showed 88.9% less pathogen population in soil as compared to control. The use of biocontrol agents decreased the stress indicator enzymes and malondialdehyde content by 55–70% and 62%, respectively as compared to control. The denaturing gradient gel electrophoresis (DGGE) analysis showed significant variations in the fungal and bacterial community structures of all treatments resulted from UPGMA cluster analysis. This study showed that S. goshikiensis YCXU could be a potential biocontrol agent for controlling watermelon Fusarium wilt disease.

Suppression of Fusarium Wilt Caused by Fusarium oxysporum f. sp. niveum Race 2 on Grafted Triploid Watermelon.

Fusarium wilt of watermelon, caused by the soilborne fungal pathogen Fusarium oxysporum f. sp. niveum race 2, is a serious, widespread disease present in major watermelon-growing regions of the United States and other countries. 'Fascination,' a high yielding triploid resistant to race 1, is grown in southeastern states in fields that contain a mixture of races 1 and 2. There is some benefit to using cultivars with race 1 resistance in such fields, even though Fascination is susceptible to Fusarium wilt caused by race 2. Experiments in 2012 and 2013 were done in fields infested primarily with race 2 and a mixture of races 1 and 2, respectively. Fascination was grafted onto four rootstock cultivars: bottle gourd (Lagenaria siceraria) 'Macis' and 'Emphasis' and interspecific hybrid squash (Cucurbita maxima× C. moschata) 'Strong Tosa' and 'Carnivor.' Nongrafted and self-grafted Fascination were used as susceptible control treatments. In both experiments, mean incidence of plants with symptoms of Fusarium wilt was ≥52% in the susceptible control treatments and ≤6% on the grafted rootstocks. Disease incidence did not differ between rootstock species or cultivars. In both years, Fascination grafted onto Strong Tosa and Macis produced more marketable-sized fruit than the susceptible control treatments. Grafted Emphasis and Carnivor also produced more fruit than the control treatments in 2012. The cucurbit rootstocks suppressed Fusarium wilt caused by race 2 and increased marketable yield of triploid watermelon grown in infested soil.

Chemical management of Fusarium wilt of watermelon

Watermelon yield loss due to Fusarium wilt is increasing in the U.S., due in part to the emergence of the virulent race 2 of Fusarium oxysporum f. sp. niveum, and to the shift in production to triploid cultivars, which generally have less host resistance than previously grown diploid cultivars. One potential management strategy is the use of soil-applied fungicides to reduce Fusarium wilt. The U.S. national program, interregional project 4 (IR-4) supported multistate trials of soil-applied chemicals to manage Fusarium wilt of watermelon. Greenhouse trials were conducted in Maryland, Indiana and Georgia to test the efficacy of 14 chemicals on Fusarium wilt. Based on the performance of these chemicals in the greenhouse, six in Maryland and Delaware and eight in Indiana were selected for subsequent field evaluations. These chemicals were applied once, as a drench at planting, in field trials in Maryland, Indiana, and Delaware in 2008. The fungicides prothioconazole, acibenzolar-S-methyl, and thiophanate-methyl resulted in the greatest reduction in Fusarium wilt, and caused no phytotoxicity. In Maryland and Indiana in 2009, these chemicals were applied through the drip irrigation line alone and in combination, at 0, 2 and 4 weeks after planting. The experiment was repeated in 2010 in Maryland. Prothioconazole alone and in combination with acibenzolar-S-methyl or/and thiophanate-methyl resulted in the greatest decrease in the area under the disease progress curve (AUDPC) of Fusarium wilt of watermelon in Maryland in 2009. The same trend was observed in 2010 in Maryland where three of the prothioconazole treatments ranked the lowest of all treatments and prothioconazole in combination with thiophanate-methyl had significantly lower Fusarium wilt AUDPC compared to the non-treated control. All chemical applications except for acibenzolar-S-methyl in combination with prothioconazole reduced Fusarium wilt AUDPC in Indiana in 2009. Prothioconazole alone and prothioconazole in combination with thiophanate-methyl ranked lowest in Fusarium wilt AUDPC, although not significantly lower than most other treatments. These studies are the first to demonstrate that the soil-applied fungicides prothioconazole and thiophanate-methyl may provide an additional field management option for Fusarium wilt of watermelon.

Root exudates of wheat are involved in suppression of Fusarium wilt in watermelon in watermelon-wheat companion cropping

Fusarium wilt disease in watermelon is widespread and responsible for serious economic losses. Petri dish experiments were performed to assess the effect of root exudates of 10 wheat varieties on mycelium growth of Fusarium oxysporum f. sp. niveum (Fon). The results showed that D123 wheat root exudates significantly inhibited mycelial growth of Fon. Pot experiments were performed to investigate the responses of Fusarium wilt in watermelon to companion cropping with D123 wheat. The results showed that watermelon seedlings suffered less Fusarium wilt in a companion system as compared to a monoculture system. Compared with monoculture, companion cropping with D123 wheat decreased malondialdehyde content and guaiacol peroxidase activities in watermelon roots after inoculation with Fon, and companion cropping with D123 wheat increased the polyphenol oxidase activities before Fon inoculation and 15 days after Fon inoculation. Companion cropping with D123 wheat slightly increased β-1, 3-glucanase and chitinase activities in watermelon roots compared with monoculture. Companion cropping with D123 wheat decreased phenylalanine ammonia-lyase activities in watermelon roots at 5 days after Fon inoculation and increased phenylalanine ammonia-lyase activity at 15 days after Fon inoculation compared with monoculture. The jasmonic acid and shikimate–phenylpropanoid–lignin biosynthetic genes were induced during the early stage of Fon infection in companion cropping compared to monoculture. It is suggested that companion cropping with D123 wheat alleviated Fusarium wilt in watermelon by inhibiting the mycelial growth of Fon and by inducing physiological changes and gene expression to protect the watermelon from injury.

Impact of Five Cover Crop Green Manures and Actinovate on Fusarium Wilt of Watermelon.

Triploid watermelon cultivars are grown on more than 2,023 ha in Maryland and in Delaware. Triploid watermelon cultivars have little host resistance to Fusarium wilt of watermelon (Fusarium oxysporum f. sp. niveum). The effects of four different fall-planted cover crops (Vicia villosa, Trifolium incarnatum, Secale cereale, and Brassica juncea) that were tilled in the spring as green manures, and bare ground, were evaluated alone and in combination with the biocontrol product Actinovate (Streptomyces lydicus) on Fusarium wilt severity and watermelon fruit yield and quality. Six field experiments were conducted over 3 years in Beltsville and Salisbury, MD and Georgetown, DE. Both V. villosa and T. incarnatum significantly suppressed Fusarium wilt of watermelon as much as 21% compared with watermelon in nonamended plots. However, no suppression of Fusarium wilt occurred at low disease levels or where low cover crop biomass was present. In general, Beltsville, MD had lower disease levels than Salisbury, MD and Georgetown, DE. T. incarnatum was the only cover crop that yielded significantly more fruit than nonamended treatments (129% more fruit per hectare) but only for one field trial. The Actinovate product either did not reduce Fusarium wilt or the magnitude of the reduction was nominal. Actinovate significantly reduced Fusarium wilt by 2% in 2009 and as much as 7% in 2010, and increased Fusarium wilt severity by 2.5% in 2011. Actinovate significantly increased yield for one field trial but only when applied to nonamended or Secale cereal-amended plots. This is the first report of a reduction in Fusarium wilt following a T. incarnatum cover crop incorporated as a green manure.

Control of Fusarium Wilt of Watermelon by Grafting onto Bottlegourd or Interspecific Hybrid Squash Despite Colonization of Rootstocks by Fusarium

Grafting watermelon (Citrullus lanatus var. lanatus) onto rootstocks of interspecific hybrid squash (Cucurbita moschata × C. maxima), bottle gourd (Lagenaria siceraria), or citron (Citrullus lanatus var. citroides) has been used in Asia and Israel to mange Fusarium wilt of watermelon caused by Fusarium oxysporum f. sp. niveum. The objectives of this study were to determine the frequency of infection of six rootstocks by F. oxysporum f. sp. niveum races 1 and 2 and the field performance of grafted rootstocks in Charleston, SC. Grafted and nongrafted watermelon and rootstock plants were inoculated in the greenhouse with race 1, race 2, or water (the control treatment). With both races, the frequency of recovery of F. oxysporum from scion and rootstock portions of inoculated watermelon plants grafted onto 'Ojakkyo' citron was greater than from watermelon plants grafted onto 'Shintosa Camel' and 'Strong Tosa' interspecific hybrid squash, and from plants grafted onto 'Emphasis', 'Macis', and 'WMXP 3945' bottlegourd. For nongrafted plants inoculated with race 1, percent recovery also was greater from Ojakkyo than from interspecific hybrid squash and bottlegourd. For nongrafted plants inoculated with race 2, F. oxysporum was recovered from the base of ≥79% of all inoculated plants. More than two-thirds (15) of 21 isolates recovered from the tops or scions of inoculated plants were pathogenic on watermelon. In spring 2010 and 2011, the six rootstocks were grafted with seedless watermelon 'Tri-X 313', which is susceptible to both races, and transplanted in a field infested with races 1 and 2 of F. oxysporum f. sp. niveum. Disease incidence for nongrafted and self-grafted Tri-X 313 (the control treatments) and Tri-X 313 grafted onto Ojakkyo citron did not differ significantly. Grafted watermelon plants produced greater weights and numbers of fruit than plants of the two control treatments. Nonpathogenic isolates of F. oxysporum and isolates of F. oxysporum f. sp. niveum colonized interspecific hybrid squash, bottlegourd, and grafted watermelon. The rootstocks evaluated, however, restricted movement of F. oxysporum f. sp. niveum into the watermelon scion, suppressed wilt symptoms, and increased fruit yields in an infested field.

Bio-organic fertilizer application significantly reduces the Fusarium oxysporum population and alters the composition of fungi communities of watermelon Fusarium wilt rhizosphere soil

Watermelon Fusarium wilt is one of the most severe soil-borne diseases caused by Fusarium oxysporum f. sp. niveum. In this study, the population of F. oxysporum was quickly monitored by real-time PCR and DNA array in watermelon Fusarium wilt infected soils treated with Paenibacillus polymyxa SQR21 enhanced bio-organic fertilizer (BIO) at the beginning of nursery growth and/or at the beginning of transplanting. The fungal community composition was investigated by molecular cloning and DGGE techniques. The real-time PCR results showed the F. oxysporum population in the rhizosphere soil decreased from 8.56 × 104 colony-forming units (cfu) g−1 rhizosphere soil to 9.41 × 103 cfu g−1 rhizosphere soil after BIO application and the DNA array detection signals of F. oxysporum population weakened. The difference between F. oxysporum abundance of BIO amended and not amended bulk soils was lower than 104 cfu g−1 soil. DGGE profile indicated that BIO application changed the fungal community structure in the rhizosphere soils; the molecular cloning data revealed that consecutive applications of BIO at nursery and transplanting stages not only decreased Ascomycota and increased Basidiomycota abundance in the rhizosphere soil but also caused the apperance of unique fungal group which were not found in the control. The beneficial fungi Chaetomium sp. Aspergillus penicillioides were found in the BIO amended treatment, while some harmful fungi such as F. oxysporum, Rhizoctonia solani, and Fusarium solani were only detected in the control. Data from this study indicated that BIO application can control watermelon Fusarium wilt by suppressing the population of F. oxysporum and changing the fungal community structure in the rhizosphere soils.

Variation of rhizosphere bacterial community in watermelon continuous mono-cropping soil by long-term application of a novel bioorganic fertilizer

The application method for a novel bioorganic fertilizer (BIO) was developed to improve its biocontrol efficacy of Fusarium wilt (Ling et al. 2010). However, its efficacy on controlling Fusarium wilt and the variations of microbial community after long-term application for watermelon production had not been elucidated. To clarify, a 4-years pot experiment of mono-cropping watermelon was conducted. The results revealed that though the disease incidences were increased in all treatments with the increase of continuous cropping years, the treatment of BIO application both in nursery and pot soil always maintained the lowest disease incidence. The real-time PCR results showed that the population of Paenibacillus polymyxa was decreased with continuous cropping years, but in all seasons, the treatment with BIO application both in nursery and pot soil had a highest population of P. polymyxa than the other treatments. On the other hand, the abundance of the pathogen FON was increased with the increase of continuous cropping years and the lowest rate of increase was found by BIO application in both nursery and pot soil. DGGE patterns showed that the bacterial diversity was weakened after mono-cropping of watermelon for 4 years, but the consecutive applications of BIO at nursery and transplanting stage resulted in the minimal change of bacterial diversity. More detailed differences on bacterial diversity between control and double application of BIO treatment after 4-years monoculture were analyzed by 454 pyrosequencing, which showed the dominant phyla found in both samples were Firmicutes, Proteobacteria and Actinobacteria, and the consecutive applications of BIO recruited more beneficial bacteria than control, such as Bacillus, Paenibacillus, Haliangium, Streptomyces. Overall, these results, to a certain extent, approved that the consecutive applications of BIO at nursery and transplanting stage could effectively suppress watermelon Fusarium wilt by regulating the rhizosphere bacterial diversity. These results could give some clues that how to regulate the soil microbial community to an appropriate level which can keep the plant healthy and thus control the soil-borne diseases.

Outbreak of Fusarium wilt in seedless watermelon seedlings in the Northern Territory, Australia

Watermelon Fusarium wilt caused by Fusarium oxysporum f. sp. niveum was first detected in the Northern Territory, Australia in May 2011. The disease affected seedlings and plants from three triploid seedless watermelon varieties from six locations. Pathogenicity tests were conducted and the fungus was shown to be pathogenic. This outbreak is the first report of Fusarium wilt in triploid seedless watermelons with symptoms similar to bacterial leaf blotch and typical wilt in Australia.

稻秸蓝藻混合厌氧发酵沼液及其化学物质对尖孢镰刀菌西瓜专化型生长的影响

研究稻秸与蓝藻(1∶1)混合厌氧发酵的沼液及其微量化学成分对尖孢镰刀菌西瓜专化型(<em>Fusaruim oxysporum </em>f. sp. <em>niveum</em>,FON)的孢子萌发、孢子数量、菌丝生长的影响。结果表明:40%浓度的发酵沼液即可100%抑制孢子萌发,20%浓度的沼液即可达到98.74%的抑制菌体产生孢子,100%浓度的沼液显著抑制气生菌丝的生长;进一步GC-MS分析发现沼液有机物成分中烷类较多,存在微量的四氯化碳(CCl₄)、六氯乙烷(C₂Cl₆)、1,1-二乙氧基乙烷(CH₃CH(OCH₂CH₃)₂)3种化学物质;三者都具有显著的抑菌效果,且随浓度的增加而增大,尤其CH₃CH(OCH₂CH₃)₂的抑菌效果最好;0.75%浓度的3种化学物质对孢子萌发的抑制率即可达到100%;在培养基中分别加入CCl₄、C₂Cl₆、CH₃CH(OCH₂CH₃)₂的浓度为1.00%时,镰刀菌的产孢数量分别降低了5.67%、18.05%、8.72%;培养4d,三者对尖孢镰刀菌西瓜专化型气生菌丝生长的抑制效果均达到90.40%,效果显著。研究表明沼液中确实存在对病原微生物具有明显抑制作用的多种有效的化学成分,可作为防治病原菌的首选药剂。;Fusarium wilt of watermelon caused by <em>Fusarium oxysporum</em> f. sp. <em>niveum</em> is world wide in occurrence, which belongs to Fungal soil-borne diseases. Spore germination, mycelial growth and sporulation are important stages of disease spread, the medicament which can block any growth stage of pathogenic bacteria can control the disease. The effect of microchemical substances in anaerobic fermented liquid from rice straw and cyanobacteria(1∶1)on <em>Fusaruim oxysporum</em> f. sp. <em>niveum</em> growth was investigated. It included spore germination, spore number, and mycelial growth. The results showed that spore germination number reduced 6.25%、37.5%、77.5% respectively at the 5%, 10% and 20% concentration groups, especially inhibited by 100% at 40% concentration of biogas slurry. The spore production could be inhibited by 98.74% at 20% concentration of biogas slurry. The aerial mycelial growth could be almost inhibited at 100% concentration of biogas slurry. Further analysis by gas chromatograph-mass spectrometer found that there are many kinds of alkyl substances in the organic component from biogas liquid. Three microchemical substances, CCl₄, C₂Cl₆, CH₃CH(OCH₂CH₃)₂ measured in biogas liquid by GC-MS analysis had distinct inhibition effects. The inhibition effects increased with their concentrations, especially CH₃CH(OCH₂CH₃)₂. The spore germination number reduced 20.22%、28.84%、40.82% respectively when CCl₄, C₂Cl₆ and CH₃CH(OCH₂CH₃)₂ were added in culture medium at the 0.1% concentration; and the inhibition rate respectively increased to 81.27%、79.78%、86.52% at 0.5% concentration. The spore germination were inhibited by 100% at the 0.75% concentration of three chemicals; The numbers of producing-spore reduced 5.67%、18.05%、8.72% respectively at the 1% concentration of three chemicals; The inhibition rate was 80.91%, 75.59% and 99.22% respectively at 3% concentration of three chemicals. The restraint effects of three chemicals were very notable on the aerial mycelial growth with training four days, especially CH₃CH(OCH₂CH₃)₂ at 0.10%-1.00% concentration and CCl₄ or C₂Cl₆ at the concentration more than 0.25%. The inhibiting rate would get to 90.4% when three chemicals at 1.00% concentration were added in the medium. The tolerance of <em>Fusarium oxysporum</em> f. sp. <em>niveum</em> on three microchemical substances increased with prolonging culture time. The aerial mycelium in every tested group grown at some extent. The restraint rate of three chemicals was 77.96% on the aerial mycelial growth with training seven days, especially 1,1-CH₃CH(OCH₂CH₃)₂ getting to 87.22%. The restraint effects increased with the concentration in the range of 0.10% to 1.00%. But the inhibiting rate declined slightly comparing with four days at same period. The experiment results showed that three chemicals remarkably restrained the growth of prophase aerial mycelial. Multi-specific ingredients were included in the biogas liquid to inhibit the pathogenic microbe. Biogas slurry can be used to control the growth of pathogenic microbes as one of the preferred agents, which will resolve the long-troubled problem about the disease and provide reference to prevent fusarium wilt of watermelon for the future study.

Co-producing iturin A and poly-γ-glutamic acid from rapeseed meal under solid state fermentation by the newly isolated Bacillus subtilis strain 3-10

The strain 3-10 was isolated from soil and identified as B. subtilis according to morphological and physiological characteristics and nucleotide sequence of 16S rRNA. It co-produced anti-fungal iturin A and fertilizer synergist of poly-γ-glutamic acid (γ-PGA) under solid state fermentation (SSF) with rapeseed meal. The co-production of iturin A and γ-PGA reached 5.3 and 51.3 g/kg-dry weight culture, respectively, and the number of viable cells reached 1.9 × 10(10) CFU/g-dry weight culture. In pot tests, the shoot length and dry weight of watermelon seedlings treated by the SSF culture improved by 48.0 and 30.8%, respectively compared to the control; and its biocontrol effect on watermelon fusarium wilt achieved 89.6%. These results highlight a novel strategy to exploit the low-cost and widely available rapeseed meal as dual-functional bio-organic fertilizer under SSF by B. subtilis.

Succinic acid inhibited growth and pathogenicity of in vitro soil-borne fungus Fusarium oxysporum f. sp. niveum

To clarify possible mechanisms of interaction of soil–plant–microbe for fusarium wilt of watermelon, succinic acid was added into the media to test its effect on in vitro Fusarium oxysporum f. sp. niveum in the ecological and biogeochemical cycling of soil–plant–microbe. Results showed that succinic acid decreased the growth and conidia germination of Fusarium oxysporum f. sp. niveum. The biomass and the conidia germinating rate were reduced by 10.1–59.8% and 14.4–21.4% respectively. Mycotoxin production and pathogenic enzyme activity by the fungus were suppressed at higher concentrations of succinic acid. Results suggested that succinic acid would not increase the risk of Fusarium oxysporum attacking plants, animals and humans due to its inhibition of fungus in the ecological and biogeochemical cycling of succinic acid in the interaction of soil–plant–microbe.

Fusarium wilt of water melon caused by Fusarium solani in Hungary

Fusarium wilt of water melon caused byFusarium solaniin HungaryWater melon growers in Hungary have been recently reported a disease resembling that of Fusarium wilt developed on Fusarium resistant cultivars. Diseased samples from different regions of Hungary were collected in 2008 and 2009. The pathogen has been successfully isolated and identified asFusarium solani.All of the isolates are host specific, but are very aggressive on water melon cultivars resistant toF. oxysporumf.sp. niveum. Severe infections occurred only in those fields where water melon has been grown continously for several years, but the pathogen is present in the soil of other fields as well.

Paenibacillus polymyxa SQR-21 systemically affects root exudates of watermelon to decrease the conidial germination of Fusarium oxysporum f.sp. niveum

Paenibacillus polymyxa SQR-21 has been identified as a potential agent for the biocontrol of Fusarium wilt in watermelon, which is caused by the pathogenic fungus Fusarium oxysporum f.sp. niveum (FON). In the present study, the effects of root exudates from watermelon plants inoculated or non-inoculated with either SQR-21 or FON on conidial germination of FON were investigated. Compared to the control, conidial germination was decreased with root exudates from SQR-21-inoculated plants, but conidial germination was enhanced by root exudates from FON-inoculated plants. Maximal germination was found with root exudates from FON-inoculated plants after 30 d, which was 1.35 times more germination than the control. A split-root system was designed to verify that the alterations of the exudation pattern in SQR-21- inoculated or FON-inoculated watermelon roots were not only local, but also systemic. Cinnamic acid was found in the watermelon root exudates. An assay to test the effects of cinnamic acid on conidial germination of FON revealed that the stimulation of conidial germination was observed from cinnamic acid concentrations ranging from 0 to 30 μg/ml. In conclusion, both of SQR-21 and FON systemically affects watermelon root exudates. These results will help to the better understanding of the plant-microbe communication and will guide to improve the biocontrol strategies against Fusarium wilt of watermelon plants.