Evaluation of arbuscular mycorrhiza and other biocontrol agents in managing Fusarium oxysporum f. sp. Cubense infection in banana cv. Neypoovan

Panama wilt of banana caused by Fusarium oxysporum f. sp. cubense (race 1) is a serious disease devastating the important cultivar Neypoovan (syn Elakki Bale AB) in southern India. Chemical control methods are not very effective in controlling the disease. The objective of this study was to evaluate biocontrol agents (BCAs) under controlled and field conditions for their efficacy against the pathogen and to detect and quantify the reduction in FOC population. Arbuscular mycorrhizal (AM) fungi, Trichoderma harzianum and Pseudomonas fluorescens were inoculated at the time of planting in single, dual and tripartite combinations allowing colonization up to 0, 45 and 90 days. Plants were challenged thereafter with 50 g of FOC inoculum multiplied on sorghum grains containing 1.5×10⁶ cfu g^?1. Uninoculated plants and those inoculated with pathogen only were controls. Plant growth parameters were measured and structural modifications in the roots were studied. FOC populations in the roots were determined by ELISA every month and final yield was recorded. At the end of 7 months, plants pre-inoculated with BCAs i.e., G. mosseae+T. harzianum and challenged with Fusarium under field conditions could sustain 61 and 70% improvement in plant height and girth, respectively, and 75% in bunch weight over plants not precolonised with BCAs but challenged with FOC which finally succumbed to the disease. ELISA study revealed Fusarium population was reduced to 0.58 OD in 7 months in G. mosseae and T. harzianum treatment compared to a level of 1.9 OD in Fusarium alone treated plants. Beneficial effect of BCAs may be due to the over all protection provided by them by causing physical modifications in the cell wall, growth promotion and through induction of disease resistance.     

Effect of combination of bio-agents and mineral nutrients for the management of alfalfa wilt pathogen Fusarium oxysporum f. sp. medicaginis

Abstract

Biological and nutrient management of soil borne disease is increasingly gaining stature as a possible practical and safe approach. Inhibitory effects of fungal and bacterial antagonists were tested under in vitro conditions against the wilt pathogen of alfalfa Fusarium oxysporum f. sp. medicaginis. Trichoderma harzianum and Pseudomonas fluorescens (PI 5) were found to be effective against the alfalfa wilt pathogen. Manganese sulphate at 500 and 750 ppm inhibited the mycelial growth of F. oxysporumf. sp. medicaginis under in vitro conditions. In pot culture studies, manganese sulphate at 12.5 mg/kg reduced the wilt incidence (23.33%). Combined application of manganese sulphate 12.5 mg/kg + T. harzianum 1.25 mg/kg of soil significantly reduced the wilt incidence accompanied by improved plant growth and yield in pot culture. The mixture of manganese sulphate (25 kg/ha) + T. harzianum (2.5 kg/ha) significantly reduced the wilt incidence when applied as a basal dose in the field conditions. The average mean of disease reduction was 62.42% over control.     

Studies on the population dynamics and integrated management of Fusarium oxysporum f. sp. psidi (Fop), a cause of guava (Psidium guajava) wilt

To assess the impact of non-host crops intercropping, bioagents and oil cakes, on population dynamics of Fusarium oxysporum f. sp. psidii (Fop) and wilt of guava. Lowest population of Fop was recorded in garlic followed by intercropping with marigold with reduction of 84.9 and 83.9%, respectively. Bioagents viz; Aspergillus niger, Trichoderma viride and Trichoderma harzianum reduced the Fop population significantly, with the lowest in T. harzianum followed by A. niger. Garlic bulb extract exhibited maximum inhibition of Fop growth (2.7 cm) followed by marigold (2.4 cm), respectively, over control. Neem cake significantly reduced population of Fop, closely followed by mahua cake, over control. Integration of neem cake + T. harzianum + garlic reduced the Fop population significantly, over control, followed by neem cake + T. harzianum + marigold but neem cake + T. harzianum + marigold reduced wilt disease significantly in comparison to neem cake + T. harzianum + garlic inter-cropping.     

Formulation and Delivery of the Bacterial Antagonist Bacillus subtilis for Management of Lentil Vascular Wilt Caused by Fusarium oxysporum f. sp. lentis

Different formulations of Bacillus subtilis were prepared using standard laboratory protocols. Bacillus subtilis survived in glucose and talc powders at 8.6 and 7.8 log₁₀ CFU/g, respectively, for 1 year of storage at room temperature compared with 3.5 log₁₀ CFU/g on a peat formulation. Glasshouse experiments using soil and seed treatments were conducted to test the efficacy of B. subtilis for protecting lentil against the wilt disease caused by Fusariumoxysporum f. sp. lentis. Seed treatments with formulations of B. subtilis on glucose, talc and peat significantly enhanced its biocontrol activity against Fusarium compared with a treatment in which spores were applied directly to seed. The formulations decreased disease severity by reducing colonization of plants by the pathogen, promoting their growth and increased the dry weight of lentil plants. Of these treatments the glucose and talc‐based powder formulations were more effective than the peat formulation and the spore application without a carrier. It was shown that the B. subtilis spores applied with glucose were viable for longer than those applied with other carriers. Seed treatment with these formulated spores is an effective delivery system that can provide a conducive environment for B. subtilis to suppress vascular wilt disease on lentil and has the potential for utilization in commercial field application.     

Relationship of in vitro and in planta screening: improving the selection process for biological control agents against Fusarium root rot in row crops

Fusarium root rot in row crops is typically managed by cultural practices and fungicide seed treatments. Biological control using microbial agents is another option but needs further development for improved disease management. Screening to identify biocontrol agents are crucial. However, relationships among the steps and how to improve the screening process are unresolved questions. Strains of Burkholderia (4), Bacillus (5) and Trichoderma (26) were studied in vitro against six Fusarium pathogens. All the bacteria and five selected Trichoderma strains were tested in planta in the greenhouse against diseases of Fusarium graminearum and Fusarium oxysporum. Burkholderia ambifaria C628, Bacillus simplex R180, and all Trichoderma isolates showed high reduction in disease levels in corn, soybean and wheat, ranging from 16 to 63%. Responses of the biocontrol agents during in vitro and in planta screening did not always correlate. In vitro and in planta tests should be considered independently in selecting biocontrol candidates.     

Development of a TaqMan Real‐Time Polymerase Chain Reaction Assay for Detection and Quantification of Fusarium oxysporum f. sp. lycopersici in Soil

Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici (FOL), is an important disease of tomato. Pathogenicity and vegetative compatibility tests, although reliable, are laborious for the identification of FOL isolates and cannot efficiently quantify population densities of FOL in the soil. The objective of this study was to develop a rapid, sensitive and quantitative real‐time polymerase chain reaction (PCR) assay for detecting and quantifying FOL in soil. An inexpensive and relatively simple method for soil DNA extraction and purification was developed based on bead‐beating and a silica‐based DNA‐binding method. A TaqMan probe and PCR primers were designed using the DNA sequence of the species‐specific virulence gene SIX1, which is only present in isolates of FOL, not in isolates of other formae speciales or non‐pathogenic isolates of F. oxysporum. The real‐time PCR assay successfully amplified isolates of three races of FOL used in this study and quantified FOL DNA in soils, with a detection limit of 0.44 pg of genomic DNA of FOL in 20 μl of the real‐time PCR. A spiking test performed by adding different concentrations of conidia to soil showed a significant linear relationship between the amount of genomic DNA of FOL detected by the real‐time PCR assay and the concentration of conidia added. In addition, the real‐time PCR assay revealed a significant quadratic regression for a glasshouse experiment between disease severity and DNA concentration of FOL. The soil DNA extraction method and real‐time PCR assay developed in this study could be used to determine population densities of FOL in soil, develop threshold models to predict Fusarium wilt severity, identify high‐risk fields and measure the impact of cultural practices on FOL populations in soils.     

Evaluation of a Peroxyacetic Acid Disinfectant in Hot-water Treatment for the Control of Basal Rot (Fusarium oxysporum f. sp. narcissi) and Stem Nematode (Ditylenchus dipsaci) in Narcissus

Formaldehyde is used routinely in the hot-water treatment (HWT) of narcissus bulbs for the control of stem nematode (Ditylenchus dipsaci) and basal rot (caused by Fusarium oxysporum f.sp. narcissi). Formaldehyde is unpleasant for operators to use, and does not kill all of the thick-walled chlamydospores of F. oxysporum and so less hazardous but more effective materials are being sought. Peroxyacetic acid (as Jet 5, a commercial disinfectant containing 5% peroxyacetic acid) was evaluated in vitro and in a field trial as a possible alternative to formaldehyde. In laboratory studies, peroxyacetic acid (as 1% Jet 5) was as effective as formaldehyde (as 0.5% commercial formalin containing 38 to 40% formaldehyde) in killing free-swimming stem nematodes and nematodes in the wool stage. Peroxyacetic acid (as 0.5% Jet 5) killed F. oxysporum chlamydospores within 1 h, whereas total kill was not achieved with formaldehyde (concentration as above) after 4 h. In a 2 year field trial, there was no evidence of detrimental effects on a healthy narcissus stock due to using peroxyacetic acid. In an infested, diseased stock, bulbs were virtually destroyed by stem nematode within 2 years when HWT was not given. The greatest reduction in nematode symptoms, and the highest bulb yields, were found when formaldehyde or the higher rates of peroxyacetic acid were used in combination with thiabendazole.     

Combined application of botanical formulations and biocontrol agents for the management of Fusarium oxysporum f. sp. cubense (Foc) causing Fusarium wilt in banana

Plant products along with biocontrol agents were tested against Fusarium wilt of banana caused by Fusarium oxysporum f. sp. cubense (Foc). Of the 22 plant species tested, the leaf extract of Datura metel (10%) showed complete inhibition of the mycelial growth of Foc. Two botanical fungicides, Wanis 20 EC and Damet 50 EC along with selected PGPR strains with known biocontrol activity, Pseudomonas fluorescens 1, Pf1 and Bacillus subtilis, TRC 54 were tested individually and in combination for the management of Fusarium wilt under greenhouse and field conditions. Combined application of botanical formulation and biocontrol agents (Wanis 20 EC + Pf1 + TRC 54) reduced the wilt incidence significantly under greenhouse (64%) and field conditions (75%). Reduction in disease incidence was positively correlated with the induction of defense-related enzymes peroxidase (PO) and polyphenol oxidase (PPO). Three antifungal compounds (two glycosides and one ester) in D. metel were separated and identified using TLC, RP-HPLC (Reverse Phase-High Pressure Liquid Chromatography) and mass spectrometry. In this study it is clear that combined application of botanical formulations and biocontrol agents can be very effective in the management of Fusarium wilt of banana.