Management Of Fusarium Wilt Disease
The exclusion of pathogen is essential for having pathogen free areas. F. oxysporum f. sp. cubense may not be eradicated from an area once it is infested .So quarantine regulations are needed.The regional awareness and contingency programs should be considered in all threatened areas (Ploetz et al. 2015).Management Of Fusarium Wilt Disease
Rotations and inter cropping reduces the accumulation of host specific pathogens in the soil and at the same time changes the microbiological niche of the soil.Banana plantations can be rotated with crops like paddy, sugarcane, cassava and cereals (Buddenhagen, 2009).
Beside, Huang et al. (2012) reported that rotation of Chinese leek-banana is efficient in
for controlling Fusarium wilt of banana as it reduced the Fusarium wilt incidence by 88%-97%. The crop rotation practices are less effective for strong soil pathogens like Foc. Effective weed management strategies and removal of asymptomatic alternate hosts from the infected banana fields can prevent and check the spread of the Fusarium wilt disease (Hennessy et al.2005).
Chemical methods showed least effective in controlling Fusarium wilt disease of banana in the field.The fungicides belonging to the benzimidazole group such as benomyl, carbendazim and thiabendazole showed effectiveness in controlling Foc in in vitro and in greenhouse conditions (Nel et al. 2007). Other chemical compounds such as cyproconazole, propiconazole and prochloraz showed Fusarium wilt disease reduction of around 80% in banana plants (Nel, 2004).Management Of Fusarium Wilt Disease
Fusarium showed maximum in rhizosphere soil (83.4) and minimum in rhizoplane (46.3) while while it showed 71.6% occurrence in infected stem and 51.6% in collar region. The pathogenicity of this dominant pathogen confirmed that it is responsible for banana wilting causing similar wilting symptoms. In vitro evaluation, plant leaf extracts showed more or less inhibitory effect on mycelial growth. Extracts of Ranunculus sceleratus showed highest inhibition of mycelial growth (97.3%) against test fungus Fusarium (Kumar,2016).
Biological control
In the developing countries Banana comes in the category of staple food.So it is consumed and exported widely even to developed countries. The Fusarium wilt worldwide is the devastating disease of the banana. Control strategies like soil fumigation, crop rotation, flood –fallowing and organic amendments tried but the problem could not be resolved effectively except by planting resistant cultivars. Planting of resistant varieties may not be acceptable every where because of consumer preference.Therefore biocontrol by use of antagonistic microbes, which protect and promote plant growth by colonizing and multiplying in the rhizosphere and plant system remains alternative. The biological control of Fusarium wilt disease has become increasingly popular being its eco friendly nature and allowing the popular susceptible banana varieties and search for novel mechanisms of plant protection using other microorganisms( Pushpavathi et al.,2016).
Many control strategies for Fusarium wilt of banana have been tried viz.,soil fumigation, fungicides (Lakshmanan et al., 1987); crop rotation (Su et al., 1986), flood –fallowing (Stover, 1962) organic amendments (Stover, 1987) and plant extracts(Kumar,2016).This disease could not be controlled effectively except by planting of resistant cultivars (Moore et al., 1999). For consumer preference the planting of resistant varieties also cannot be implemented (Viljoen, 2002). Use of antagonistic microbes is a potential alternative and has become increasingly popular (Weller et al., 2002). Biological control of soil borne diseases caused especially by Fusarium oxysporum is now well documented (Thangavelu et al., 2004). There are reports demonstrating successful use of different species of Trichoderma, Pseudomonas, Streptomyces, non pathogenic Fusarium (npFo) of both rhizospheric and endophytic nature against Fusarium wilt under both glass house and field conditions (Rajappan et al., 2002; Getha et al., 2005). Results of the glasshouse evaluations of Nel et al(2006) revealed that two of the nonpathogenic F. oxysporum isolates, CAV 255 and CAV 241, reduced fusarium wilt incidence by 87•4 and 75•0%, respectively.Management Of Fusarium Wilt Disease
Pushpavathi et al. (2015) reported that sucker treatment before planting with biocontrol agents either Trichoderma viride or Pseudomonas fluorescens and soil drenching with same biocontrol agents twice at 30 and 180 DAP as booster application.This effectively reduced the disease incidence and intensity thereby increasing the yield.
Trichoderma spp.
This fungus is free living and common in soil and root ecosystems. This could interact well in root, soil and foliar environments and release a variety of compounds inducing localized or systemic resistance response in plants. This has long been known as biological agents used in the disease management have ability for increasing root growth, development, crop productivity, resistance to abiotic stresses ,uptake and use of nutrients. This can be efficiently used as spores (especially, conidia)being tolerant to adverse during product formulation and field application in comparision to their mycelia and chlamydospores (Amsellem et al., 1999). The mycelial mass is a key component in production of antagonistic metabolites (Yedidia et al., 2000). The investigations revealed that Trichoderma species can effectively suppress Fusarium wilt pathogens (Thangavelu et al., 2004). Thangavelu (2002) reported that on application of T. harzianum Th-10 formulation @ 10 g/plant containing 4×1031 cfu/g in basal + top dressing on 2, 4 and 6 months after planting showed highest reduction of disease incidence (51.16%).This was followed through Bacillus subtilis or Pseudomonas fluorescens (41.17%) applications as talc based formulation under both glass house and field conditions. The talc based formulation of T. harzianum Th-10 and ‘carbendazim (0.1 per cent) recorded only 40.1% and 18.1% reduction of the disease respectively. In the Fusarium wilt-nematode complex system also, soil application of biocontrol agents significantly reduced the wilt incidence and also the root lesions and root knot index. In addition to this, 50 to 82% of reduction in nematode population viz., Pratylenchus coffeae and Meloidogyne incognita was also observed due to application of bioagents and the maximum reduction was due to T. harzianum treatment (Thangavelu, 2002). Raghuchander et al. (1997) found that T. viride and P. fluorescens to be equally effective in reducing the wilt incidence.While inoculation of potted abaca plants with T.viride and yeast showed 81.76% and 82.52% reduction of wilt disease severity respectively (Bastasa and Baliad, 2005).Management Of Fusarium Wilt Disease
Soil application of T. viride NRCB1, as chaffy grain formulation,significantly reduced the external (up to 78%) and internal symptoms (up to 80%) of Fusarium wilt in tissue cultured as well as sucker derived plants of banana.It also increased the plant growth parameters significantly as compared to the talc powder formulation both under pot culture and field conditions (Thangavelu and Mustaffa, 2010).
The possible mechanisms involved in reducing severity of Fusarium wilt severity due to Trichoderma spp. treatment may be the mycoparasitism, spatial and nutrient competition, antibiosis by enzymes and secondary metabolites and induction of plant defence system. The mycoparasitism shows coiling, disorganization of host cell contents and penetration of the host (Papavisas, 1985;). In the mycoparasitism of Trichoderma spp. it parasitizes the hyphae of the pathogen and produces extracellular enzymes such as proteolytic -1, 3- glucanolytic enzymes and chitinase etc which results lysis of the pathogen. The toxic metabolites such as extracellular enzymes, volatiles and antibiotics like gliotoxin and viridin which are highly fungistatic substances (Weindling, 1941) got actively involved in antibiosis. Inspite of this Trichoderma spp. could compete and sequester ions of iron through releasing compounds known as siderophores (Srinivasan et al., 1992). There are several reports demonstrating control of a wide range of plant pathogens including Fusarium spp. by Trichoderma spp. through action of extracellular enzymes during mycoparasitic reaction. Thangavelu and Musataffa (2010) highlighted the application of T. viride NRCB1 as rice chaffy grain formulation and challenge inoculation with Foc resulted in the induction of defense related enzymes such as Peroxidase and Phenylalanine Ammonia lyase (PAL) and also the total phenolic content significantly higher (>50%) as compared to control and Foc alone inoculated banana plants and the induction was maximum at 4-6th day after treatment. They reported that increased activities of these lytic enzymes and thus increased content of phenols in the T. viride applied plants induced resistance against Foc by either making physical barrier stronger or chemically impervious to the hydrolytic enzymes produced of the pathogen (Thangavelu and Mustaffa, 2010).Management Of Fusarium Wilt Disease
Pseudomonas spp.
Pseudomonas spp. comes in the category of useful agricultural biocontrol agents because they can use many exudates/compounds serving as a nutrient source (Lugtenberg et al., 1999). They show high growth rate,produces diverse mechanisms of actions against phytopathogens and produces a wide range of antagonistic metabolites (Lugtenberg et al., 1999).They are easy to culture in vitro and can be reintroduced into the rhizosphere (Rhodes and Powell, 1994) and can induce systemic resistance to pathogens (Pieterse et al., 2001). Many investigations revealed ability of P. fluorescens to suppress Fusarium wilt disease of banana. Fluorescent pseudomonad species such as Pseudomonas fluorescens (Sakthivel and Gnanamanickam, 1987), Pseudomonas putida (de Freitas and Germida, 1991), Pseudomonas chlororaphis (Chin-A-Woeng et al., 1998) and Pseudomonas aeruginosa (Anjaiah et al., 2003) have been tried to inhibit pathogens to promote growth and yield in many crop plants. Sivamani and Gnanamanickam (1988) investigated that seedlings of Musa balbisiana treated with P.fluorescens expressed less severe wilting along with internal discoloration due to Foc infection in green house experiments. The bacterized seedlings showed better root growth having enhanced plant height. Thangavelu et al. (2001) found that P. fluorescens strain pf10 isolated from the rhizosphere of banana roots are potent to detoxify fusaric acid produced by Foc race-1 and reduced wilt incidence by 50%. Dipping of suckers in the suspension of P. fluorescens along with the application of 500 g of wheat bran and saw dust inoculation (1: 3) of the respective bio-control agent effectively checked Fusarium wilt incidence in banana (Raghuchander et al., 1997). Rajappan et al. (2002) found that the talc based powder formulation of P. fluorescens strain pf1 was effective against Foc in the field. P. fluorescens strain WCS 417 having power to suppress other Fusarium wilts checking incidence by 87,4% in Cavendish bananas in glasshouse trials (Nel et al., 2006). Saravanan et al.(2003) reported that basal application of neem cake at 0.5 kg/plant + sucker dipping in spore suspension of P. fluorescens for 15 min + soil application of P. fluorescens at 10 g/plant at 3, 5 and 7 months after planting checked the wilt.Otherwise the basal application of neem cake at 0.5 kg/plant + soil application of P. fluorescens at 10 g/plant at 3, 5 and 7 months after planting showed the greatest check of wilt disease in two field trials conducted in Tamil Nadu, India.
Fishal et al. (2010) evaluated capability of Pseudomonas sp. (UPMP3) and Burkholderia sp. (UPMB3) obtained from healthy oil palm roots in induction of resistance fighting against F. oxysporum f. sp. cubense race 4 on susceptible Berangan banana in glasshouse conditions. This revealed that preinoculation of banana with Pseudomonas sp UPMP3 produced 51% reduction in wilt disease severity.Whereas the combined application of either UPMP3 + UPMB3 or single application of UPMB3 registered only 39 and 38% reduction, respectively.Management Of Fusarium Wilt Disease
Ting et al.(2011)investigated that among six endobacteria isolates only two isolates (Herbaspirillum spp and Pseudomonas spp.) produced volatile compounds capable of inhibiting the growth of Foc race 4. The identified compounds were 2- pentane 3-methyl, methanethiol and 3-undecene. They reported that the isolate Herbaspirillum spp. recorded 20.3% inhibition of growth of Foc race 4 as its volatile compounds contained all the three compounds whereas Pseudomonas isolate AVA02 recorded only 1.4% of growth inhibition of race 4 Foc as its volatile compounds contained only methanethiol and 3 undecene. Presence of all three compounds especially 2- pentane 3-methyl in high quantity is very important for the antifungal activity against Foc. Of the 56 fluorescent pseudomonad isolates obtained from banana rhizosphere, Pseudomonas aeruginosa strain FP10 displayed the most potent antibiosis towards the Foc. This produced IAA, siderophores and phosphate-solubilizing enzyme indicating that this strain also has plant growth promoting power. The presence of DAPG gene (ph1D) in the strain FP10 was confirmed by PCR and the production of DAPG was confirmed by TLC, HPLC and FT-IR analyses. The in-vivo bioassay carried out showed that the strain FP10 exhibited increased plant height (30.69cm) and reduced the vascular discolouration (24.49%), whereas, the pathogen Foc alone-inoculated plants had an average height (21.81 cm) and vascular discolouration 98.76% (Ayyadurai et al., 2006).
Saravanan and Muthusamy (2006) found talc based preparation of P. fluorescens when applied in soil @ 15 g/plant in banana it checked significantly wilt disease caused by Fusarium.The power in P. fluorescens for suppressing Fusarium depends on its potential to produce antibiotic -2, 4- Diacetylphloroglucinol (DAPG). DAPG obtained from P. fluorescens when treated to soil significantly inhibited spore germination and growth in Foc. The soil extracts on inoculation of P. fluorescens produced less quantity of DPAG.Management Of Fusarium Wilt Disease