Evaluation of Some Fungi and Bacteria for Potential Control of Safflower Rust

Some fungal and bacterial isolates applied as soil and seed treatments in greenhouse trials gave a good protection against Puccinia carthami Cda. on safflower, significantly reducing the infection from rust-infested seeds. Trichoderma viride and T. harzianum added alone and in combination as air-dried inoculum to the soil were the most effective fungal isolates. However T. viride at two higher rates reduced the rate of emergence of safflower seedlings. Among bacteria, Bacillus subtilis, B. cereus, isolates of Pseudomonas fluorescens and B. thuringiensis reduced rust infection when added both as soil drench and as seed treatment. Good results in the biocontrol of P. carthami were also obtained with some combination antagonist treatments such as T. viride + B. cereus, T. viride + P. fluorescens (16), T. viride + T. harzianum + B. cereus and T. viride +, T. harzianum + P. fluorescens (16). Fungal isolates added as soil treatment increased seedling length, whereas no similar effects were observed when these isolates were applied as seed treatment.     

Biological control of root-rot of Coleus forskohlii Briq. using microbial inoculants

The root-rot or wilt of Coleus forskohlii is a very serious soil-borne disease caused by Fusarium chlamydosporum. A field study was undertaken to study the possibility of controlling the disease using three biocontrol agents viz., Glomus mosseae, Pseudomonas fluorescens, Trichoderma viride, singly and in combination. Planting of coleus cutting was done in wilt sick soil. Inoculation with Trichoderma viride + Glomus mosseae gave the best result in controlling the disease. The same treatment also resulted in maximum growth, yield and root forskolin concentration of coleus. Plants treated with T. viride + G. mosseae showed a disease severity index of 33.28% compared to uninoculated control plants, which had a maximum disease severity index of 85.5%. The fungicide Emisan (0.2%) was not as effective as the biocontrol agents in controlling the pathogen.     

Biological control of white rot of onion

Summary Interactions of 123 isolates of fungi, 17 of bacteria and 22 of actinomycetes, respectively, withSclerotium cepivorum were studied in agar culture. They were grouped into 4 different types of reactions. Amongst themTrichoderma viride, Fusarium graminearum, Coniothyrium minitans andGliocladium roseum inhibited the growth ofS. cepivorum and later grew over its colony.T. viride showed a characteristic coiling around the hyphae ofS. cepivorum. T. viride andF. graminearum prevented the development of sclerotia.C. minitans was found to parasitize the sclerotia ofS. cepivorum and produced its pycnidia within them.Aleurisma carnis, Cladosporium elatum, Penicillium expansum, P. nigricans, P. notatum, P. piscarium, P. puberulum, P. rolfsii, P. urticae, P. variabile, Tilachlidium humicola andHelminthosporium sp. inhibited the growth ofS. cepivorum at a distance. Eleven isolates of bacteria and 3 ofStreptomyces sp. showed pronounced antagonistic properties againstS. cepivorum.Experiments were carried out to study the effects on white rot development in soil of organisms selected from agar plate tests. None of the antagonistic micro organisms had any deleterious effects on onion growth. Of the organisms testedP. nigricans gave the best results in controlling white rot infection.This work was carried out at the Department of Botany, The University, Birmingham, England. I wish to thank Prof.C. J. Hickman for his invaluable advice and encouragement.     

Biological control ofRhizoctonia solani in strawberry fields byTrichoderma harzianum

Summary Trichoderma harzianum preparations was used in two successive field experiments in commercial strawberry nurseries and fruiting fields. Disease severity ofRhizoctonia solani in daughter plants was reduced by 18–46 % in the treated nursery plots. Infestation of nursery soil with the pathogen, as tested by planting beans in soil samples was reduced by the Trichoderma treatment by up to 92% as compared to the untreated control. A rapid decline of the disease was observed in soil fromT. harzianum treated plots, successively planted with bean seedlings. More isolates ofTrichoderma sp. antagonistic toR. solani, were found in the infested field as compared to the non infested one.Trichoderma harzianum treated plants, transferred to the commercial field gave a 21–37% increase in early yield of strawberries. A combined treatment in the nursery and in the fruiting field resulted in a 20% yield increase as compared to control plots.     

Studies on some fungi isolated from the rhizosphere of tomato plants and the consequent prospect for the control of Verticillium wilt

Summary Biological control of Verticillium wilt disease with antagonistic micro-organisms was studied. Antagonism of some fungi, isolated from tomato rhizosphere, toVerticillium albo-atrum R & B. was observedin vitro. A clearly defined zone, in which the growth of the pathogen was inhibited, was observed withPenicillium spp. (includingPenicillium chrysogenum Thom) andFusarium culmorum (S.G. Sm) Sacc., whileTrichoderma viride pers. ex Fries,Gliocladium spp. andPenicillium vermiculatum Dangeard, suppressed the growth ofV. albo-atrum by penetrating, and overgrowing it. OnlyT. viride andP. vermiculatum culture filtrate added to the Dox's agar, reduced the radial growth ofV. alboatrum. Root-dip application of culture filtrates ofT. viride andP. chrysogenum was found to be most effective in controlling the disease, followed by other species ofPenicillium andGliocladium spp. WhileFusarium culmorum provided no control. Improvement of plant height and vigour with a better yield due to culture filtrate treatment occurred. Root-dip application of antagonistic fungal propagules (T. viride, P. chrysogenum) to tomato seedlings was also very effective in controlling wilt in tomato plants grown inV. albo-atrum infested soil. Dedicated to the memory of the late Prof. Ivor Isaac with whom I had the pleasure of working     

Fungi pathogenic to ryegrass seedlings

Summary Fungi borne on or in ryegrass (Lolium spp.) seeds or invading ryegrass seedlings grown on field soils were isolated and identified. Selected isolates were tested to determine their pathogenicity to ryegrass seedlings. Seed-borne fungi were generally weakly virulent or non-pathogenic to ryegrass seedlings. Pathogenic seed-borne fungi includedChaetomium globosum Kunze: Fr.,Curvularia trifolii (Kauffm.) Boedijn, and species ofPenicillium Link andAspergillus Mich. ex Link. Species of fungi isolated from seedlings grown on field soils de pended on soil and temperature. Soil-borne fungi pathogenic to seedlings includedFusarium avenaceum (Fr.) Sacc.,F. culmorum (W. G. Smith) Sacc.,F. equiseti (Corda) Sacc.,F. oxysporum Schlecht.: Fr.,F. solani (Mart.) Sacc.,Pythium afertile Kanouse and Humphrey,P. debaryanum auct. non Hesse,P. irregulare Buisman,P. ultimum Trow, a sphaerosporangiatePythium sp.,Chaetomium globosum, Thanatephorus cucumeris (Frank) Donk,Trichoderma koningii Oudem., and aPhomopsis sp. Individual isolates of fungi differed in virulence to ryegrass seedlings, and ryegrass cultivars differed in susceptibility to seedling pathogens.     

Enhanced activity of introduced biocontrol agents in solarized soils and its implications on the integrated control of tomato damping-off caused by Pythium spp

Soil solarization in combination with introduction of biocontrol agents (BCA) was evaluated as a potential disease management strategy for tomato damping-off caused by Pythium spp. A rifampicin resistant Pseudomonas fluorescens strain (PfT-8) and a carbendazim resistant Trichoderma harzianum strain (ThM-1) were introduced into soil following solarization. Tomato seeds were planted into treated field plots. The influence of soil solarization and application of biocontrol agents on damping-off incidence, plant biomass, rhizosphere population of introduced antagonists, and native Pythium spp. was assessed by two consecutive field trials. Damping-off incidence was significantly reduced in solarized plots compared to control. Soil inoculation of biocontrol agents into solarized plots resulted in the highest suppression of damping-off incidence (PfT-8 up to 92%; ThM-1 up to 83%), and increase in plant biomass (PfT-8 up to 66%; ThM-1 up to 48%) when compared to un-solarized control plots. Rhizosphere population of introduced biocontrol agents gradually increased (PfT-8 up to 102% and ThM-1 up to 84%) in solarized soils when compared to unsolarized control. The population of Pythium spp in rhizosphere soil was reduced up to 55% in solarized plots; whereas, application of BCA to solarized soils reduced the rhizosphere population of Pythium spp. by 86 and 82% in P. fluorescens and T. harzianum applied plots respectively.     

Arbuscular mycorrhizal fungi and Trichoderma viride mediated Fusarium wilt control in tomato

The biocontrol potential of two arbuscular mycorrhizal fungi (AMF) (Funneliformis mosseae and Acaulospora laevis) and Trichoderma viride was assessed against tomato wilt caused by Fusarium oxysporum Schlecht. f. sp. lycopersici under pot condition. All the bioagent showed appreciable results in increasing plant growth. Combined inoculation of F. mosseae, A. laevis and T. viride showed maximum increases in plant height, shoot fresh weight, root dry weight, number of leaves and number of branches per plant while dual inoculation of F. mosseae and T. viride increased rest of the growth parameters like shoot dry weight, root fresh weight, root length and leaf area. AM colonisation and spore number was found highest in single inoculation of AMF, which decreases with the addition of T. viride. But, this decrease has no effect on biocontrol efficiency of bioagents. Photosynthesis, chlorophyll content and nutrient content were markedly decreased by pathogen infection. Bioagent application overcomes this effect and a remarkable increase in the plant phosphorus and nitrogen content was recorded. Among both the AMF, F. mosseae proved to be more effective strain compared to A. laevis for tomato. Maximum reduction in disease incidence and severity was recorded in combined inoculation of F. mosseae, A. laevis and T. viride. Whereas control plants without any bioagent showed maximum occurrence of disease. The findings of this study concludes that soil inoculation with F. mosseae along with root inoculation with conidial suspension of T. viride before transplantation offered better survival and resistance to tomato seedlings against Fusarium wilt.     

Eco-friendly approaches for the management of fenugreek root rot

To evolve eco-friendly management of fenugreek root rot caused by Rhizoctonia solani, a field trial was conducted during Kharif 2002 and Rabi seasons of 2002–2003 and 2003–2004. Experiments were conducted with eight treatments and three replications in RBD using the variety CO-2. The pooled analysis of the three season data showed that seed treatment with Trichoderma viride at 4g/kg of seed + soil application of Trichoderma viride at 5 kg/ha + soil application of neem cake at 150 kg/ha (T₃) recorded a percent disease index (PDI) of 23.1 versus 65.5 PDI in the control which accounted for a disease reduction of 64.7%. It was on par with seed treatment with Trichoderma viride at 4g/kg of seed + soil application of T. viride at 5 kg/ha (T₂) which reduced the disease incidence by 62.3% (24.7 PDI). The chemical treatment used for comparison, i.e. seed treatment with carbendazim + soil drenching at 0.1% + soil application of neem cake at 150 kg/ha recorded the lowest PDI of 16.8 with 74.4% disease reduction. Among the various treatments T₃ gave a seed yield of 572.7 kg/ha followed by T₂ (555.7 kg/ha). Treatment T₇ recorded the highest yield of 578.7 kg/ha. In the control plot the recorded yield was only 359.3 kg/ha. Though T₃ was more effective at reducing the disease incidence than T₂, the C:B ratio was higher (1:9.1) in respect of T₂ than T₃, which gave a C:B ratio of only 1:3.9. Hence, seed treatment with T. viride at 4g/kg + soil application of T. viride at 5kg/ha is a cost effective, eco-friendly management strategy for fenugreek root rot.     

Antagonistic Activities of Trichoderma harzianum Against Pythium aphanidermatum and Pythium myriotylum on Tobacco

Trichoderma harzianum rendered Pythium aphanidermatum and P. myriotylum non-viable in Petri dish dual culture. The Pythium mycelia from such cultures showed natural autofluorescence in the regions of interactions, indicating their death. Non-volatile and volatile fungicidal activities were detected in T. harzianum culture. Lytic activity of β-(l,3)-glucanase was detected on the cell walls of the Pythium spp. There was a significant decrease in the disease incidence when T. harzianum was incorporated into sterile soil, whereas the effect was insignificant in natural soil.     

Fungal Antagonists of Gerlachia nivalis

Trichoderma viride was strongly antagonistic to Gerlachia nivalis in agar plate culture and it controlled infection of barley seedlings from seed-borne inoculum when incorporated in soil as straw culture and from soil-borne inoculum when conidia were applied to the seed coat. Penicillium expansum and Papulaspora byssina were inhibitory towards G. nivalis in culture, although not as strongly as T. viride, and they did not control seedling infection as effectively.     

Control of Pythium damping-off of sugar beet by seed treatment with crop straw powders and a biocontrol agent

Seed treatment with non-sterilized powdered straws from 39 crops was tested for the control of Pythium damping-off of sugar beet. Four straws, including flax, coriander, pea, and lentil were effective in controlling the disease in soil artificially infested with Pythium sp. “group G.” Sterilizing flax and pea straws eliminated the efficacy of these straws. Wheat straw powder coated on sugar beet seeds increased the incidence of Pythium damping-off but this effect was reversed by the co-inoculation of wheat straws with the biocontrol agent Pseudomonas fluorescens 708. Coating sugar beet seeds with P. fluorescens 708 and flax or pea straws also increased the efficiency of the bacterial strain for the control of Pythium damping-off. Pea straws and to a lesser extent lentil straws produced volatile substances that affected mycelial growth of Pythium sp. “group G” on potato dextrose agar in Petri plates when the straws were mixed with water and left to ferment for two days. Fermentation of pea straws led to the accumulation of volatile ammonia, which was produced by the reduction of the large amount of nitrate stored in the straw. Reduction of nitrate and therefore the release of volatile ammonia did not occur in sterilized pea straws. However, fermenting sterile pea straws with bacteria from different genera restored nitrate reduction and the release of volatile ammonia, suggesting that microorganisms associated with pea straws are responsible for the conversion of nitrate into volatile ammonia which in turn control Pythium damping-off disease in sugar beet.     

Biocontrol efficacy of Trichoderma spp. against sesame wilt caused by Fusarium oxysporum f. sp. sesami

Sesame (Sesamum indicum L.) is one of the most important oilseed crops in Egypt and worldwide. It is being infected with many pathogens, among these pathogens Fusarium oxysporum f.sp. sesami (Zap.) Cast is causing severe economic losses on sesame. In this study, antagonistic capability of 24 isolates of Trichoderma spp. was assessed in vitro against F. oxysporum f.sp. sesami. Two strains; T. harzianum (T9) and T. viride (T21) were revealed to have high antagonistic effect against F. oxysporum f.sp. sesami in vitro with inhibition percentage about 70 and 67%, respectively. These two isolates proved to have high ability to control Fusarium wilt disease under greenhouse conditions. The highest reduction in disease severity was achieved with T. viride followed by T. harzianum with reduction in disease severity about 77 and 74%, respectively. This study revealed that the time of application of bioagents is a decisive factor in determining the efficacy of Trichoderma isolates to control Fusarium wilt of sesame. It was revealed that the highest reduction in the disease severity was achieved when either Trichoderma viride or T. harzianum were applied 7 days before challenging with the F. oxysporum f.sp. sesami.     

Possible Role of Xanthobaccins Produced by Stenotrophomonas sp. Strain SB-K88 in Suppression of Sugar Beet Damping-Off Disease

Three antifungal compounds, designated xanthobaccins A, B, and C, were isolated from the culture fluid of Stenotrophomonas sp. strain SB-K88, a rhizobacterium of sugar beet that suppresses damping-off disease. Production of xanthobaccin A in culture media was compared with the disease suppression activities of strain SB-K88 and less suppressive strains that were obtained by subculturing. Strain SB-K88 was applied to sugar beet seeds, and production of xanthobaccin A in the rhizosphere of seedlings was confirmed by using a test tube culture system under hydroponic culture conditions; 3 μg of xanthobaccin A was detected in the rhizosphere on a per-plant basis. Direct application of purified xanthobaccin A to seeds suppressed damping-off disease in soil naturally infested by Pythium spp. We suggest that xanthobaccin A produced by strain SB-K88 plays a key role in suppression of sugar beet damping-off disease.     

The effect of volatile and gaseous metabolites of swelling seeds on germination of fungal spores

Effects of volatile and gaseous metabolites of swelling seeds of pea, bean, wheat, corn, cucumber, tomato, lentil, carrot, red pepper and lettuce on germination of spores of five genera of fungi were found to depend rather on the fungal than on the plant genus. Germination of spores ofBotrytis cinerea, Mucor racemosus andTrichoderma viride was most severely inhibited. Spores ofVerticillium dahliae were less sensitive and germination of spores ofFusarium oxysporum was inhibited only in two cases. On the other hand, exudates of pea and bean stimulated germination of spores ofFusarium oxysporum. Also spores ofTrichoderma viride germinated better in an atmosphere enriched with exuded metabolites of swelling lettuce seeds. When carbon dioxide produced by the swelling seeds was absorbed in potassium hydroxide, spores ofTrichoderma viride andVerticillium dahliae did not germinate at all, the inhibitory effects of volatile and gaseous exudates on germination of spores ofMucor racemosus were accentuated, and also the percentage of germinated spores ofFusarium oxysporum decreased. Germination of spores ofBotrytis cinerea was not influenced. Absorption of volatile and gaseous metabolites in a solution of potassium permanganate decreased in most cases their inhibitory effects, particularly inBotrytis cinerea.     

Biological control of wood decay in an open tropical environment with Penicillium sp. and Trichoderma viride

The ability of Penicillium sp. and Trichoderma viride to retard the decay of obeche (Triplochiton scleroxylon) wood in the field for 11 months (January–November) covering dry and wet seasons in a tropical environment was investigated using the ‘graveyard’ method. Inoculation of stakes with Gloeophyllum sp. or G. sepiarium (decay fungi) 24 h after treatment with T. viride or Penicillium sp. in January (dry season) did not increase decay after 11 months. Total inhibition of the decay fungi was indicated since the low weight losses of stakes was not markedly different from losses in control stakes biologically treated but not exposed to decay fungi. Inhibition of the activities of other unidentified field fungi was also indicated because weight losses were greater in uninoculated and untreated stakes. However, decay occurred in stakes biologically treated in January but later exposed to decay fungi in May, after the dry season. A repeat application of T. viride treatment in May, to stakes earlier treated in January, markedly reduced decay following exposure to decay fungi in September (wet season). A similar Penicillium sp. application was not as effective as T. viride application because unlike the T. viride protected stakes, decay was greater in stakes twice protected with Penicillium sp. but not exposed to decay fungi. The results indicate that repeated application of biocontrol agents may be important for controlling wood decay following the adverse effect of the dry season.     

Tropical field assessment of combined Trichoderma viride Proteus sp. and urea protective treatment of wood against biodeterioration

Two previous reports showed that decay of wood blocks was inhibited by treatment with combined phosphate buffer (pH7) and Trichoderma viride or urea and ureolytic Proteus sp. A field assessment of the two treatment strategies was therefore carried out in the tropical rainforest for 24 months using the “grave yard method”. The groundline region of stakes treated with buffer/T. viride succumbed to biodegradation after 8 months as indicated by loss of resistance to compression, occurrence of basidiomycete and soft-rot cavities. This was attributed to leaching due to the heavy rainfall, soil microflora and the failure of T. viride to spread due to the dry season effect at the onset of the trials. No signs of degradation were evident until 18 months in stakes treated with urea and Proteus sp. The addition of T. viride to the urea/Proteus treatment system caused a marked improvement as no signs of biodegradation were observed throughout the duration of the field trial. As the concentration of ammonia declined, the hitherto suppressed T. viride began to spread and “fill in the gap”. It can be concluded that the triple combination of urea, Proteus sp. and T. viride, can significantly extend the service life of timber in the field.     

Direct effect of biocontrol agents on wilt and root-rot diseases of sesame

In Egypt, sesame cultivation is subject to attack by wilt and root-rot diseases caused by Fusarium oxysporum f.sp. sesami (Zap) Cast. and Macrophomina phaseolina (Maubl) Ashby causing losses in quality and quantity of sesame seed yield. Bacillus subtilis and Trichoderma viride isolates which were isolated from sesame rhizosphere were the most effective to antagonise fungal pathogens, causing high reduction of hyphal fungal growth. Trichoderma viride was found to be mycoparasitic on Fusarium oxysporum f.sp. sesami and M. phaseolina causing morphological atternation of fungal cells and sclerotial formation. In general, Bacillus subtilis, T. viride, avirulent Fusarium oxysporum isolate and Glomus spp. (Amycorrhizae) significantly reduced wilt and root-rot incidence of sesame plants at artificially infested potted soil by each one or two pathogens. Data obtained indicate that Glomus spp significantly reduced wilt and disease severity development on sesame plants followed by T. viride. Meanwhile, avirulent Fusarium oxysporum isolate followed by Glomus spp. were effective against root-rot disease incidence caused by M. phaseolina. Glomus spp. followed by B. subtilis significantly reduced wilt and root-rot disease of sesame plants. All biotic agents significantly reduced F. oxysporum f.sp. sesami and M. phaseolina counts in sesame rhizosphere at the lowest level. Glomus spp. and the avirulent isolate of F. oxysporum eliminated M. phaseolina in sesame rhizosphere. Meanwhile T. viride was the best agent at reducing F. oxysporum at a lower level than other treatments. Application of VA mycorrhizae (Glomus spp.) in fields naturally infested by pathogens significantly reduced wilt and root-rot incidence and it significantly colonised sesame root systems and rhizospheres compared to untreated sesame transplantings.     

Use of a Colonization-Deficient Strain of Escherichia coli in Strain Combinations for Enhanced Biocontrol of Cucumber Seedling Diseases

Seed treatments containing combinations of Escherichia coli S17R1 and Burkholderia cepacia Bc-B provided significantly greater (P ≤ 0.05) suppression of cucumber seedling pathogens in a field soil naturally infested with Pythium and Fusarium spp. than seeds treated individually with strains Bc-B, S17R1, or Enterobacter cloacae 501R3. Although strain S17R1 had no effect on disease severity when applied alone and did not colonize cucumber rhizosphere, it enhanced the biocontrol effectiveness of strain Bc-B.     

Biocontrol of <Emphasis Type="Italic">Pythium</Emphasis> damping-off in cucumber by arbuscular mycorrhiza-associated bacteria from the genus <Emphasis Type="Italic">Paenibacillus</Emphasis>

The Pythium biocontrol features of 17 Paenibacillus strains, all previously isolated from the rhizosphere, hyphosphere or bulk soil from mycorrhizal and non-mycorrhizal cucumber plants, were examined using a cucumber seedling emergence bioassay. Thirteen strains – four strains of Paenibacillus polymyxa, eight strains of P. macerans and one strain of Paenibacillus sp. – significantly increased the percentage of seedling emergence of seeds inoculated with agar plugs of Pythium aphanidermatum FC42. Overall, the efficacy of Pythium biocontrol did not seem to differ between isolates of Paenibacillus originating from either mycorrhizal or non-mycorrhizal systems. No strains significantly reduced the damping-off incidence caused by the aggressive isolate Pythium sp. B5. Two strains of P. macerans not only reduced the incidence of pre-emergence damping-off by 73%, but they also counteracted the plant growth-depressing effect of P. aphanidermatum FC42, so that 68–82% of the emerged seedlings remained healthy 7 days after sowing. Two strains of P. macerans and one strain of P. polymyxa also significantly increased the percentage of seedling emergence following inoculation with approximately 10⁵ zoospores of P. aphanidermatum FC42. There was no significant difference between the dry weight of three selected bacteria-inoculated and -uninoculated plants in the absence of Pythium; however, the dry weight of bacteria-inoculated plants was significantly higher than that of the uninoculated control plants with bacteria in the presence of P. aphanidermatum FC42.