Reduced Fusarium Wilt Research Articles

Efficacy of Various Fungal and Bacterial Biocontrol Organisms for Control of Fusarium Wilt of Tomato.

Numerous fungi and bacteria, including existing biocontrol strains with known activity against soilborne fungal pathogens as well as isolates collected from the roots and rhizosphere of tomato plants growing in the field, were tested for their efficacy in controlling Fusarium wilt of tomato. Tomato seedlings were treated with the potential biocontrol agents in the greenhouse and transplanted into pathogen-infested field soil. Organisms tested included nonpathogenic strains of Fusarium spp., Trichoderma spp., Gliocladium virens, Pseudomonas fluorescens, Burkholderia cepacia, and others. Specific nonpathogenic isolates of F. oxysporum and F. solani collected from a Fusarium wilt-suppressive soil were the most effective antagonists, providing significant and consistent disease control (50 to 80% reduction of disease incidence) in several repeated tests. These isolates also were equally effective in controlling Fusarium wilt diseases of other crops, including watermelon and muskmelon. Other organisms, including isolates of G. virens, T. hamatum, P. fluorescens, and B. cepacia, also significantly reduced Fusarium wilt compared to disease controls (30 to 65% reduction), but were not as consistently effective as the nonpathogenic Fusarium isolates. Commercially available biocontrol products containing G. virens and T. harzianum (SoilGard and RootShield, respectively) also effectively reduced disease (62 to 68% reduction) when granules were incorporated into potting medium at 0.2% (wt/vol). Several fungal and bacterial isolates collected from the roots and rhizosphere of tomato plants also significantly reduced Fusarium wilt of tomato, but were no more effective than other previously identified biocontrol strains. Combinations of antagonists, including multiple Fusarium isolates, Fusarium with bacteria, and Fusarium with other fungi, also reduced disease, but did not provide significantly better control than the nonpathogenic Fusarium antagonists alone.

BIOLOGICAL CONTROL OF FUSARIUM WILT OF MUSKMELON BY FORMULATIONS OF ASPERGILLUS NIGER

Aspergillus niger van Tiegh. (An 27) was shown to be a promising biocontrol agent against Fusarium oxysporum Schlecht f. sp. melonis Sny. and Hans., which causes muskmelon wilt. Fruit wastes, such as carrot waste, citrus peels and pomace, mixed fruit pomace, and pineapple peels and pomace, proved to be a promising and cheap alternative source for mass multiplication of A. niger. These wastes are readily available throughout the year and can replace some of the highly priced media used for mass production of biocontrol organisms. Citrus pomace extract (20%) was found to be an excellent liquid medium for mass production. In solid fermentation, fruit wastes were superior to other media used as substrates. A short period of 10 days of incubation was sufficient for the production of 108 colony forming units (cfu) per gram of the material. The extent of control achieved by the seed coating formulation (FSC) was at par with Carbendazim. Formulation for soil application (FSO), a new contribution to the formulation science, could reduce Fusarium wilt disease by 78.31%, when applied at the rate of 8 g/kg of soil. Both FSC and FSO formulations can be stored at room temperature (14–35 °C) for more than a year.

Evaluation of antagonistic strains of Fusarium spp. in the biological and integrated control of Fusarium wilt of cyclamen

The ability of antagonistic strains of Fusarium spp. to control Fusarium wilt of cyclamen caused by Fusarium oxysporum f. sp. cyclaminis was tested under glasshouse conditions over three years. Several antagonistic strains of F. oxysporum and one strain of F. moniliforme, applied alone or in mixtures, were able to decrease significantly ( p = 0.05) the incidence of Fusarium wilt. Biological control was consistent especially when the antagonists were applied both by mixing a chlamydospore talc preparation in the potting substrate (3 × 10 4–5 × 10 5 CFU/ml of soil) two weeks before transplant and by dipping plant roots at transplant in a conidial suspension (1 × 10 7–5 × 10 8 CFU/ml). The combination of the benzimidazole fungicide carbendazim and antagonistic Fusarium spp. generally increased the efficacy of control. Carbendazim (0.5 mg a.i./ml of substrate) proved most effective in reducing or delaying the appearance of Fusarium wilt symptoms when the dosage was split into two applications, one at transplant and one 2 months later. Sodium alginate and kaolin formulations of F. oxysporum antagonistic strain 251/2 were not effective in reducing Fusarium wilt on cyclamen, while the same strain applied as chlamydospores dispersed in talc or as conidial suspension controlled the pathogen. The findings are discussed with respect to the most effective application and formulation methods of biocontrol agents under commercial conditions.

Influence of pH on Suppression of Fusarium Wilt of Carnation by Pseudomonas fluorescens WCS417r

AbstractThe influence of the nutrient solution pH on suppression of fusarium wilt by Pseudomonas flurescens WCS417r in carnation grown in rockwool was investigated.Experiments were conducted with carnation cultivars Lena and Pallas, susceptible and moderately resistant to fusarium wilt, respectively. WCS417r significantly reduced fusarium wilt in the susceptible cv. Lena, that was root‐inoculated with Fusarium oxysporum f.sp. dianthi (Fod), at pH 7.5, but not at pH 6.5 and 5.5 This corresponded with a higher in vitro siderophore production and antagonism of Fod by WCS417r at pH 7.5 than at pH 6.5 and 5.5. Fusarium wilt in the moderately resistant cv. Pallas, however, was also significantly reduced by treatment with WCS417r at pH 5.5 This corresponded with the low influence of pH on induced resistance by WCS417r in plants of cv. Pallas that were stem‐inoculated with Fod.The results indicate that the influence of pH on control of fusarium wilt of carnation by Pseudomonas fluorescens WCS417r differs between carnation cultivars that differ in their level of resistance against fusarium wilt. In susceptible cv. Lena, fusarium wilt is suppressed by antagonism by WCS417r, that is most effective at pH 7.5. In the moderately resistant cv. Pallas, fusarium wilt is suppressed by both antagonism and induced resistance by WCS417r. The latter is also effective at lower pH.

Suppression of fusarium wilt of carnation byPseudomonas putidaWCS358 at different levels of disease incidence and iron availability

Treatment with Pseudomonas putida WCS358r, a rifampicin‐resistant derivative of strain WCS358, significantly reduced fusarium wilt of carnation grown in rockwool if disease incidence was moderate, but not if disease incidence was high. Differences in disease incidence could intentionally be established by varying the inoculum density of the pathogen Fusarium oxysporum f. sp. dianthi (Fod). The effectiveness of disease suppression by WCS358r increased with decrease of inoculum density and consequently decrease of disease incidence. WCS358r and a Tn5 marked derivative of WCS358 (B243) reduced fusarium wilt of carnation most effectively if a low iron availability for the pathogen was established by adding unferrated or only partially ferrated ethylenediamine [di(o‐hydroxyphenylacetic) acid]. A Tn5 mutant of WCS358 defective in siderophore biosynthesis (JM218) did not reduce disease incidence. Siderophore production and inhibition of Fod by WCS358r in vitro decreased with increasing iron availability, supporting the more effective disease suppression by strains WCS358r and B243 at low iron availability. Siderophore‐mediated competition for iron was shown to be the mechanism of suppression of fusarium wilt of carnation by P. putida WCS358. Its effectivity was highest at a low iron availability and at a moderate disease incidence.

Chloroacetamide herbicides reduce incidence of Fusarium wilt in melons

Pretreatment of muskmelon seedlings with four chloroacetamide herbicides at 0.1 μg g −1 reduced the incidence of Fusarium wilt by 22–79%. Acetochlor also induced resistance to Fusarium wilt in watermelon and tomato seedlings inoculated with the appropriate formae speciales. Acetochlor reduced Fusarium wilt in muskmelon seedlings also when applied as a seed treatment [soaking for 5 h in solution (50 μg ml −1)] and, to a lesser extent, when applied as a foliar spray. In a field trial carried out in a naturally infested soil, acetochlor significantly reduced the incidence of Fusarium wilt in muskmelons cv. En Dor during the first 43 days postemergence. Acetochlor, and possibly other chloroacetamide herbicides, is potentially valuable in disease control.

Experiments in biological and chemical control of Fusarium wilt (F. oxysporum f. melonis (Leach and Currence) Snyd. and Hans.) of muskmelon.

Selected antagonistic biota used in the planting medium reduced Fusarium wilt of muskmelon significantly. In combined treatments they augmented control given by fungicidal amendments to infested soil and (or) seed. Combined treatments that consisted of amendments to two or more of the three treatment components, soil, seed, planting medium, frequently were more effective than treatments of one component. Retaining the jiffy pot when transplanting enhanced control given by biological and fungicidal amendments. Under conditions highly favorable for wilt, protection given by antagonistic biota in the planting medium and fungicidal amendments frequently diminished after 35 days. Although reductions in population of the pathogen to low levels did not preclude high plant losses, evidence supports the view that the minimum requirements for satisfactory control include (1) reduction of populations of the pathogen to low levels, (2) continuous protection of the host through interaction of antagonistic biota and residual biota of treated soils, and (3) resistance imparted to the host by systemic action of fungicides. Results encourage the use of the jiffy pot and the planting medium when planting in the field for protecting the plant from injury and to provide a medium in which biological and fungicidal amendments may be applied at any desired time in advance of seeding and transplanting.