Management of Fusarium wilt of banana: A review with special reference to tropical race 4

Three plant growth promoting rhizobacterial (PGPR) strains, PF1,FP7 and PB2, were tested alone and in combinations for suppression ofrice sheath blight disease and promotion of plant growth underglasshouse and field conditions The mixture of PGPR strainssignificantly reduced the sheath blight incidence when applied as eitherbacterial suspension through seed, root, foliar and soil application inglasshouse conditions, or as talc-based formulation under fieldconditions, compared to the respective individual strains The averagemean of disease reduction was 292% for single strains and451% for mixtures In addition to disease suppression, treatmentwith mixture of PGPR strains promoted plant growth in terms of increasedplant height and number of tillers, and ultimately grain yield Theaverage increases in yield for single strains were 177%, and259% in case of mixture Mixture of three PGPR strains reduceddisease and promoted growth to a level equivalent to two strainmixtures Though seed treatment of either single strain or strainmixtures alone could reduce the disease, subsequent application to root,leaves or soil further reduced the disease and enhanced the plantgrowth The mixture consisting of PF1 plus FP7 was the most effective inreducing the disease and in promoting plant growth and grainyield

A new bio-formulation containing plant growth promoting rhizobacterial mixture for the management of sheath blight and enhanced grain yield in rice

Fluorescent pseudomonads are involved in the natural suppressiveness of some soils to fusarium wilts. These bacteria have been applied successfully to suppress fusarium wilts of various plant species grown in conducive soils and growing substrates. Suppression of fusarium wilts by fluorescent pseudomonads can be ascribed to direct and indirect effects against pathogenic Fusarium oxysporum. Direct effects are expressed by a reduction of the saprophytic growth of the pathogen leading to delay and reduction of root infections. This antagonism was demonstrated to be related to siderophore‐mediated iron competition. Iron competition was also shown to enhance the antagonistic effect of non‐pathogenic F. oxysporum by making the pathogen more susceptible to fungal competition for carbon. Indirect effects of fluorescent pseudomonads against pathogenic F. oxysporum are mainly related to the induction of host plant resistance which can be associated with the bacterial lipopolysaccharides. Suppression of fusarium wil...

Suppression of fusarium wilts by fluorescent pseudomonads: Mechanisms and applications

In the last century, the banana crop and industry experienced dramatic losses due to an epidemic of Fusarium wilt of banana (FWB), caused by Fusarium oxysporum f.sp. cubense (Foc) race 1. An even more dramatic menace is now feared due to the spread of Foc tropical race 4. Plant genetic resistance is generally considered as the most plausible strategy for controlling effectively such a devastating disease, as occurred for the first round of FWB epidemic. Nevertheless, with at least 182 articles published since 1970, biological control represents a large body of knowledge on FWB. Remarkably, many studies deal with biological control agents (BCAs) that reached the field-testing stage and even refer to high effectiveness. Some selected BCAs have been repeatedly assayed in independent trials, suggesting their promising value. Overall under field conditions, FWB has been controlled up to 79% by using Pseudomonas spp. strains, and up to 70% by several endophytes and Trichoderma spp. strains. Lower biocontrol efficacy (42-55%) has been obtained with arbuscular mycorrhizal fungi, Bacillus spp., and non-pathogenic Fusarium strains. Studies on Streptomyces spp. have been mostly limited to in vitro conditions so far, with very few pot-experiments, and none conducted in the field. The BCAs have been applied with diverse procedures (e.g., spore suspension, organic amendments, bioformulations, etc.) and at different stages of plant development (i.e., in vitro, nursery, at transplanting, post-transplanting), but there has been no evidence for a protocol better than another. Nonetheless, new bioformulation technologies (e.g., nanotechnology, formulation of microbial consortia and/or their metabolites, etc.) and tailor-made consortia of microbial strains should be encouraged. In conclusion, the literature offers many examples of promising BCAs, suggesting that biocontrol can greatly contribute to limit the damage caused by FWB. More efforts should be done to further validate the currently available outcomes, to deepen the knowledge on the most valuable BCAs, and to improve their efficacy by setting up effective formulations, application protocols, and integrated strategies.

/pdf/biological-control-agents-against-fusarium-wilt-of-banana-15z1s0s521.pdf

Biological Control Agents Against Fusarium Wilt of Banana

Fusarium wilt is one of the most serious diseases caused by a soil-borne pathogen affecting banana production. The goal of this study was to evaluate the capability of a novel bio-organic fertilizer (BIO2) that integrated the biocontrol agent Bacillus subtilis N11, and mature composts to control Fusarium wilt of banana in pot experiments. The results showed that the application of the BIO2 significantly decreased the incidence rate of Fusarium wilt compared to the control. To determine the antagonistic mechanism of the strain, we also studied the colonization of the natural biocontrol agent on banana roots using a GFP marker. The studies were performed in a hydroponic culture system, a sand system and a natural soil system. The results indicated that the bacteria colonized predominantly by forming biofilms along the elongation and differentiation zones of the roots. The fact that similar observations were obtained in all three systems suggests that colonization by N11 can be studied in a defined system. The population of B. subtilis N11 in the rhizosphere and on banana roots was also monitored. We speculate that the colonization pattern of B.subtilis N11 can be linked to the mechanism of protection of plants from fungal infection.

A new bioorganic fertilizer can effectively control banana wilt by strong colonization with Bacillus subtilis N11

Native strains ofPseudomonas fluorescens exhibitedin vitro antibiosis towards isolates of races 1 and 4 ofFusarium oxysporum f.sp.cubense, the Panama wilt pathogen of banana. The seedlings ofMusa balbisiana seedlings treated withP. fluorescens showed less severe wilting and internal discolouration due toF. oxysporum f.sp.cubense infection in greenhouse experiments. In addition to suppressing Panama wilt, bacterized seedlings ofM. balbisiana also showed better root growth and enhanced plant height.

Biological control of Fusarium oxysporum f.sp. cubense in banana by inoculation with Pseudomonas fluorescens

From among 125 strains of fluorescent and 52 strains of nonfluorescent bacteria initially screened in the laboratory for their antibiosis towards the bacterial wilt pathogen, Pseudomonas solanacearum, strain Pfcp of Pseudomonas fluorescens and strains B33 and B36 of Bacillus spp., were chosen and evaluated further in greenhouse and field tests. Pfcp treated banana (Musa balbisiana), eggplant and tomato plants were protected from wilt upto 50, 61 and 95% in greenhouse and upto 50, 49 and 36% respectively in field. Protection afforded by the Bacillus strains was lower. In bacteria-treated plants which were subsequently inoculated with P. solanacearum plant height and biomass values increased and were close to those of nontreated and noninoculated control plants.

Biological control of bacterial wilt caused by Pseudomonas solanacearum in India with antagonistic bacteria

Strains of fluorescent and nonfluorescent bacteria that were isolated from rice rhizospheres of Southern India and showed antagonism towardsRhizoctonia solani were evaluated for biological control of rice sheath-blight (ShB). Efficient strains of bacteria inhibited mycelial growth ofR. solani, affected sclerotial viabilityin vitro and protected IR 20 and TKM 9 rice seedlings from infection byR. solani in greenhouse tests. Pretreatment of sclerotia in bacterial suspensions resulted in reductions in ShB lesion sizes up to 31 to 44% in IR20 and 58 to 74% in TKM 9 rice. In field plots, IR 50 and TKM 9 rice plants raised from bacterized seeds had 65 to 72% less ShB than those plants from untreated seeds.

Biological control of sheath-blight of rice in india with antagonistic bacteria

Bacterial antagonists of both fluorescent and nonfluorescent groups were screened for in-vitro inhibition of the rice sheath blight (ShB) fungus Rhizoctonai solani Kuhn and chitinase production in the laboratory. Twelve percent of the total 1,757 strains screened inhibited R. solani while 31% of the total 1,366 strains tested were positive for chitinase activity. The efficient strains were then evaluated in the field for ShB suppression. Two strains from each of the three seed-bed experiments were chosen for the field test in a hot-spot location. Additional treatments were a Bacillus and validamycin, the fungicide. There was no correlation between chitinase activity in the antagonists and ShB suppression in the seed-bed or field plots. Two most efficient Pseudomonas putida and P. fluorescens strains afforded 68 and 52% ShB suppression while validamycin afforded 27% disease control.

Biological control of rice sheath blight in India: Lack of correlation between chitinase production by bacterial antagonists and sheath blight suppression

Severity of stem-rot disease of peanut caused byRhizoctonia solani was reduced by 54.9 and 68% in plants of two cultivars treated in the greenhouse with antagonistic strains ofPseudomonas fluorescens. These strains were selected based on theirin vitro toxicity to mycelial growth and sclerotial germination ofR. solani. In field experiments, bacterization of peanuts withP. fluorescens resulted in taller plants (by 25.7%) and increased yields (by 59.0%).

S. S. Gnanamanickam

Papers

Biological control of Fusarium oxysporum f.sp. cubense in banana by inoculation with Pseudomonas fluorescens

Biological control of bacterial wilt caused by Pseudomonas solanacearum in India with antagonistic bacteria

Biological control of sheath-blight of rice in india with antagonistic bacteria

Biological control of rice sheath blight in India: Lack of correlation between chitinase production by bacterial antagonists and sheath blight suppression

Bacterization of peanut with Pseudomonas fluorescens for biological control of Rhizoctonia solani and for enhanced yield