Biological inductions of systemic resistance to collar rot of peppermint caused by Sclerotium rolfsii

The efficacy of eight fungal and eight bacterial isolates was tested for their ability to inhibit the growth of Sclerotium rolfsii, the causal agent of collar rot of peppermint. In vitro studies revealed that Trichoderma harzianum (THA) and Pseudomonas fluorescens (PFM) showed the highest inhibition of mycelial growth (68.28; 74.25 %) of S. rolfsii. The antagonists T. harzianum and P. fluorescens were compatible with each other and they were tested alone and together in in vivo for the control of S. rolfsii. Besides, the induction of defense-related enzymes such as peroxidase, polyphenoloxidase, phenylalanine ammonia-lyase, and the accumulation of phenolics in peppermint plants due to the application of bioagents were also studied. Combined application of talc-based formulation of bioagents and challenge inoculation with S. rolfsii recorded maximum induction of defense-related enzymes, and accumulation of phenolics as compared with individual application. This study suggests that the increased induction of defense-related enzymes (two- to threefold) and phenolic content (threefold) due to the combination treatment of bioagents might be involved in the reduction of collar rot incidence.     

Integrated Control of Sclerotium rolfsii on Groundnut in South Africa

Sclerotium rolfsii Sacc. causes disease of numerous crop plants worldwide, including groundnuts. Control of this pathogen is difficult as it produces sclerotia which overwinter in the soil to emerge as inoculum and cause disease the following season. Various chemical, biological and cultural control strategies have been suggested and implemented, some of which have reduced disease incidence in the field. No studies have yet been undertaken in South Africa to control this disease on groundnut, either chemically, biologically or by cultural practices. In this study, several strategies were investigated for the control of S. rolfsii on groundnuts. Difenoconazole was identified as a fungicide that could possibly be applied in combination with Trichoderma harzianum, a biological antagonist of S. rolfsii, above carbendazim and flusilazole, and chlorothalonil. Difenoconazole significantly reduced the growth rate of S. rolfsii but not of T. harzianum. The cultivation of infected fields with an inversion plough significantly reduced infection of groundnuts by S. rolfsii and also improved the quality of the produce, while yield was not increased. Lower plant density increased the incidence of disease in an infected field, and is therefore not considered to be a viable form of cultural control.     

Ecological management of tropical sugar beet (TSB) root rot (Sclerotium rolfsii (Sacc.) by rhizosphere Trichoderma species

Trichoderma species are collected from different location of sugarbeet growing areas of Tamil Nadu and it is effective against Sclerotium rolfsii pathogen caused by sugarbeet ecosystems. Out of thirty-one isolates of Trichoderma viride and four isolates of Trichoderma harzianum collected and tested for their antagonistic activity against S. rolfsii by dual culture technique, one isolate was found to be effective T. viride (TVB1) that recorded the maximum (73.03%) inhibition on the mycelial growth recording only 2.40 cm growth as against 8.90 cm in the control. The isolates of T. harzianum THB-1 recorded 71.19% mycelial growth reduction over control. The colonisation behaviour of T. viride (TVB1) revealed that it completely over grew on pathogen within 48 h after interaction with the pathogen, and speed of growth on pathogen was also high and it possesses a higher level of competitive saprophytic ability. The best four isolates of TVB1, TVB-2, TVB-3 and TVB31 and two isolates of T. harzianum THB-1 and THB-2 were compared with other species of Trichoderma longibrachiatum, Trichoderma reesei, Trichoderma koningii and Chaetomium globosum and tested under in vitro condition. BA of neem cake at 150 kg ha^?1 + T. viride isolate (TVB1) at 2.5 kg/ha recorded least root rot disease incidence of 17.05% which accounted for 75.37% disease reduction over control and highest recorded maximum root yield 65.73 t ha^?1 and increasing sugar content.     

Evaluation of biological seed treatments in combination with management practices for the control of Fusarium dry rot of potato

Seed-borne diseases of potato represent a significant constraint to potato production in the US. The use of an effective fungicide in combination with good management practices during cutting and storage, prior to planting, is essential to reducing disease. The efficacy of two biocontrol agents (Bacillus subtilis and Trichoderma harzianum), and a commercially formulated mixture of the chemicals fludioxonil plus mancozeb, applied as seed treatments in combination with different management practices, were evaluated over two years for the control of seed piece decay and sprout rot caused by Fusarium sambucinum. Treatments were made 10 days prior to planting and at planting, and tubers were re-stored at either 18 °C and 95% RH with forced air ventilation at 5950 l min⁻¹ (optimal conditions), at 25 °C in the dark without ventilation (sub-optimal), or not stored at all prior to planting. Seed piece and sprout health were evaluated in vitro and agronomic impacts evaluated in field experiments. Results showed that the biological control agents B. subtilis and T. harzianum provided good control of sprout rot and seed piece decay caused by F. sambucinum, when seed was re-stored under optimal conditions or not re-stored at all. Under optimal conditions, treatment with B. subtilis reduced sprout rot and seed piece decay on average by 66% and 84%, respectively. Treatment with T. harzianum reduced sprout rot and seed piece decay on average by 70% and 81%, respectively. Treatment with fludioxonil + mancozeb reduced sprout rot and seed piece decay under both re-storage regimes. Under optimal conditions, disease incidence and severity was reduced on average by 81% and 97%, respectively. Neither biological control agent reduced seed piece decay incidence under either re-storage regime compared to the untreated controls.     

Evaluation of Streptomyces spp. for effective management of Poria hypolateritia causing red root-rot disease in tea plants

A field study was conducted to evaluate the efficacy of indigenous biocontrol agents such as Streptomyces griseus and Streptomyces lydicus along with Bacillus subtilis and Trichoderma harzianum for controlling red root rot disease of tea plants. In response to biological treatments, disease incidence, green leaf yield, biometric and physiological parameters and organoleptic characters of made tea were assessed. Among the thirteen treatments tested, soil drenching of carbendazim was superior in terms of reducing red root rot incidence followed by combination of S. griseus and T. harzianum recorded in two consecutive field experiments. In contrast, the maximum green leaf yield and plant growth was achieved in soil application of these biocontrol agents. However, the performance of this dual combination of biocontrol agents was on par with systemic fungicide in terms of disease control. Correspondingly, the biometric, physiological and biochemical parameters were also considerably increased in biologically treated plants when compared to untreated control. The disease increased from 38.7% to 47.6% in untreated control plots and those plants were unhealthy in terms of leaf yellowing, stunted growth with heavy flowering, drying of branches and sudden death of bushes. The tea quality parameters such as theaflavin and thearubigin contents were significantly increased in the range of 0.75–1.43% and 10.38–13.22% respectively in biocontrol treated plants. This was also reflected in tea liquor characteristics. Our results suggested that the combination of biocontrol agents represent a promising alternative for effective management of red root rot disease in tea plants.     

Biological control of tomato collar rot induced by Sclerotium rolfsii using Trichoderma species isolated in Bangladesh

This study evaluated three Trichoderma strains (T. harzianum TR05, T. virens TR06 and T. asperellum TR08) originating from Bangladesh as potential biological control agents against collar rot of tomato under greenhouse conditions. After seed treatment with TR05, a disease incidence of collar rot (5.36%) was lower than for TR06 (34.2%) and TR08 (20.8%). Germination percentage of tomato was highest for TR05 (90.3%). In soil treatment, inoculation with TR08 resulted in the lowest disease incidence (9.78%), and the disease incidence was statistically no different from that for TR05 (16.4%). Thus, TR05 and TR08 have potential as biological control agents of collar rot in tomato.     

Biological and fungicidal antagonism of Sclerotium cepivorum for controlling onion white rot disease

The action of some microbial isolates and Topsin-M against the most pathogenic isolate (Sc₂) of Sclerotium cepivorum causing onion white rot was tested. Bacillus subtilis B₄, B. subtilis B₅, Trichoderma koningii and Trichoderma harzianum were the most antagonistic isolates of the causal fungus. Mycelia of sclerotial germination of S. cepivorum (Sc₂) were completely inhibited in vitro by application of 2.0 g ?L^?1 Topsin-M. In pots, disease incidence was decreased to 8.33 % by the use of Topsin-M followed by T. koningii (29.17 %) compared with 95.83 % for the control, i.e., a remarkable reduction in severity was obtained. Under field conditions, disease incidence was decreased to 2.78 % by Topsin-M and to 11.11 % by T. harzianum. Both agents caused a sharp reduction in disease severity, reaching 1.39 % and 9.72 %, respectively, with 11.80 % being achieved by T. koningii and B. subtilis B₅. A close link between the biological action and enhancement of the enzyme activities of polyphenol oxidase and peroxidase with ability of onion to resist S. cepivorum was found, indicating induction of systemic acquired resistance. Accordingly, chlorophyll, root and foliage lengths, foliar, bulb dry matter and bulb productivity were also enhanced upon application of this biological control strategy.     

Use of Trichoderma harzianum and Gliocladium vitens for the Biological Control of Post-emergence Damping-off and Root Rot of Cucumbers Caused by Pythium ultimum

The antagonist strains Gliocladium virens G2 and Trichoderma harzianum T3 originally isolated from Pythium suppressive peat, and two benomyl-resistant strains of T. harzianum, T12B and T95, were evaluated as biological control agents of damping-off and root rot of cucumbers in sphagnum peat caused by Pythium ultimum. All strains were equally effective when applied as 1 % peat-bran preparations, whereas the effectiveness of disease control was reduced at higher concentrations of the antagonists. The two wild-type strains were also found to be effective when applied as conidial suspensions, and in this case no reduction in disease control was seen at higher concentrations. G. virens G2 and T. harzianum T12B showed antibiotic activity against P. ultimum in in vitro tests; however there were no signs of mycoparasitism of P. ultimum by any of the antagonist strains.     

Influence of bio-inoculants on the control of root rot and wilt disease of pyrethrum caused by Rhizoctonia solani

The effect of four bio-inoculants namely, Glomus aggregatum, Streptomyces sp., Bacillus subtilis and Trichoderma harzianum and a fungicide, Ridomil-mancozeb was evaluated on the biomass production and control of root rot and wilt disease under glasshouse conditions. Results showed that 21-day- prior inoculation with G. aggregatum was most effective where none of the treated plants produced disease symptoms and interestingly their growth was increased by 39.4%. The colonisation by G. aggregatum (>80%) also increased P concentration in shoot. While, similar treatment with Streptomyces sp., B. subtilis, T. harzianum and Ridomil-mancozeb individually failed to produce any significant effect over Rhizoctonia solani inoculated control, where all inoculated plant died, prematurely. The simultaneous and 3-day-post treatments of G. aggregatum were non-effective but simultaneous treatment with Streptomyces sp. produced 70% disease control, while B. subtilis and T. harzianum individually provided 50% control. Their effects were either better or at par when compared with the simultaneous treatment of Ridomil-mancozeb. In 3-day-post treatment, Streptomyces, B. subtilis and Ridomil-mancozeb individually provided 50% disease control, whereas T. harzianum was least effective as it could protect only 25% plants against infection. The results reveals that 15 days prior treatment of G. aggregatum can significantly controls the root rot and wilt disease of pyrethrum. Further, treatment of Streptomyces can also serve the next effective post infection control method.     

Biocontrol of onion white rot by application of Trichoderma species formulated on wheat bran powder

In vitro, Trichoderma album, Trichoderma harzianum, Trichoderma koningii, Trichoderma viride and Trichoderma virens showed antagonistic effect against the most pathogenic isolate (Sc2) of Sclerotium cepivorum, the cause of onion white rot disease. Five Trichoderma preparations of each Trichoderma sp. were prepared on wheat bran powder to be used for controlling white rot disease of onion. Greenhouse and field experiments followed the same trend where T. harzianum and T. koningii were the most effective in reducing the incidence and severity of white rot disease compared with the control. Trichoderma species preparations caused promotion to vegetative parameters of onion plants in pots and increase bulb productivity in filed. In this regard, T. harzianum and T. koningii were the most effective. A positive correlation was found between the biocontrol activity of Trichoderma species preparations and enhancement of peroxidase, polyphenoloxidase and chitinase enzymes in onion plants to resist infection with S. cepivorum.     

Control of Root Rot and Wilt caused by Pythium myriotylum in Kangaroo Paw (Anigozanthos)

Control of root rot and wilt on Kangaroo Paw (Anigozanthos) caused by Pythium myriotylum was tested, using artificial inoculations, in greenhouse experiments. Disease incidence in the inoculated but non‐treated plots was 74% in Expt A (1999) and 46% in Expt B (2000). Disease incidence was significantly reduced by treatments with fenamidon (26 and 70%) and Terraclor SuperX (65 and 41%) in Expts A and B, respectively, in comparison with the non‐treated plots. Disease incidence was reduced with Ridomil Gold by 7 and 48% in Expts A and B, respectively; with Dynone by 22 and 41% in Expts A and B, respectively; with Tachigaren by 20% in both experiments; and with Trichoderma harzianum treatment, disease incidence was reduced by 9% only in Expt B. Yields (recorded only in Expt B) obtained in plots inoculated with P. myriotylum were significantly lower than in the non‐inoculated control plots. The most efficient treatment was fenamidon, with 324% more flowers than in the non‐treated control. The number of flowers in terraclor SuperX, Ridomil Gold, Dynone and T. harzianum treatments was higher by 285, 249, 234 and 235% than in the non‐treated control. In vitro tests demonstrated that the most effective doses, causing 50% inhibition of mycelial growth (ED₅₀), were 0.09, 0.4, 0.4 and 4 μg/ml for the fungicides fenamidon, Ridomil Gold (mefenoxam), Terraclor SuperX (etridiazole + quintozene) and Dynone (prothiocarb), respectively.     

Comparative Antagonistic Properties of Gliocladium virens and Trichoderma harzianum on Sclerotium rolfsii and Rhizoctonia solani—its Relevance to Understanding the Mechanisms of Biocontrol

An isolate of Trichoderma harzianum which is less effective than G. virens in suppressing S. rolfsii and R. solani was compared with G. virens for various mechanisms of antagonism in vitro, viz., antagonism in dual culture/hyphal parasitism, parasitism of sclerotia and antibiosis. G. virens and T. harzianum were equally effective in parasitizing the hyphae of R. solani. Only T. harzianum parasitized the hyphae of S. rolfsii, and the two antagonists were comparable with respect to antibiosis on the test pathogens. However, G. virens readily parasitized the sclerotia of the test pathogens and was found to be more effective than T. harzianum in destroying the sclerotia. Under SEM, G. virens was found to colonize, penetrate, and sporulate inside the sclerotia of the test pathogens.Parasitism of sclerotia is suggested as the principal mechanism of biological control of S. rolfsii and R. solani by G. virens.     

Enhancing biological control of basal stem rot disease (<Emphasis Type="Italic">Ganoderma boninense</Emphasis>) in oil palm plantations

Basal Stem Rot (BSR) disease caused by Ganoderma boninense is the most destructive disease in oil palm, especially in Indonesia and Malaysia. The available control measures for BSR disease such as cultural practices and mechanical and chemical treatment have not proved satisfactory due to the fact that Ganoderma has various resting stages such as melanised mycelium, basidiospores and pseudosclerotia. Alternative control measures to overcome the Ganoderma problem are focused on the use of biological control agents and planting resistant material. Present studies conducted at Indonesian Oil Palm Research Institute (IOPRI) are focused on enhancing the use of biological control agents for Ganoderma. These activities include screening biological agents from the oil palm rhizosphere in order to evaluate their effectiveness as biological agents in glasshouse and field trials, testing their antagonistic activities in large scale experiments and eradicating potential disease inoculum with biological agents. Several promising biological agents have been isolated, mainly Trichoderma harzianum, T. viride, Gliocladium viride, Pseudomonas fluorescens, and Bacillus sp. A glasshouse and field trial for Ganoderma control indicated that treatment with T. harzianum and G. viride was superior to Bacillus sp. A large scale trial showed that the disease incidence was lower in a field treated with biological agents than in untreated fields. In a short term programme, research activities at IOPRI are currently focusing on selecting fungi that can completely degrade plant material in order to eradicate inoculum. Digging holes around the palm bole and adding empty fruit bunches have been investigated as ways to stimulate biological agents.     

Involvement of phenazines and lipopeptides in interactions between Pseudomonas species and Sclerotium rolfsii, causal agent of stem rot disease on groundnut

Aims: To determine the role of phenazines (PHZ) and lipopeptide surfactants (LPs) produced by Pseudomonas in suppression of stem rot disease of groundnut, caused by the fungal pathogen Sclerotium rolfsii. Methods and Results: In vitro assays showed that PHZ‐producing Pseudomonas chlororaphis strain Phz24 significantly inhibited hyphal growth of S. rolfsii and suppressed stem rot disease of groundnut under field conditions. Biosynthesis and regulatory mutants of Phz24 deficient in PHZ production were less effective in pathogen suppression. Pseudomonas strains SS101, SBW25 and 267, producing viscosin or putisolvin‐like LPs, only marginally inhibited hyphal growth of S. rolfsii and did not suppress stem rot disease. In contrast, Pseudomonas strain SH‐C52, producing the chlorinated LP thanamycin, inhibited hyphal growth of S. rolfsii and significantly reduced stem rot disease of groundnut in nethouse and field experiments, whereas its thanamycin‐deficient mutant was less effective. Conclusions: Phenazines and specific lipopeptides play an important role in suppression of stem rot disease of groundnut by root‐colonizing Pseudomonas strains. Significance and Impact of the Study: Pseudomonas strains Phz24 and SH‐C52 showed significant control of stem rot disease. Treatment of seeds or soil with these strains provides a promising supplementary strategy to control stem rot disease of groundnut.     

Seed biopriming with novel strain of Trichoderma harzianum for the control of toxigenic Fusarium verticillioides and fumonisins in maize

Fusarium verticillioides is one of the most important fungal pathogens in maize causing both pre- and post-harvest losses and also capable of producing Fumonisins. In the present study attempts have been made for screening potential T. harzianum from native rhizosphere and to study its effect on Fusarium ear rot disease, fumonisin accumulation in different maize cultivars grown in India. Eight isolates of T. harzianum were isolated and T. harzianum isolate Th-8 exhibited better antifungal activity than carbendizim. Th-8 was formulated in different solid substrates like wheat bran, paddy husk, talcum powder and cornstarch. Maize seeds of kanchan (moderately resistant), pioneer (resistant) and sweet corn (susceptible) were selected for laboratory and field studies and these seeds were treated with a conidial suspension of T. harzianum at the rate of 1 × 10⁸ spore/ml and formulation at the rate of 10 g/kg. Treated seeds were subjected to evaluate F. verticillioides incidence, seed germination, seedling vigour and field emergence, yield, thousand seed weight and fumonisin production. It was found that the pure culture of T. harzianum was more effective in reducing the F. verticillioides and fumonisin incidence followed by Talc formulation than the carbendizim treated and untreated control. Formulations of T. harzianum were effective at reducing the F. verticillioides and Fumonisin infection and also increasing the seed germination, vigour index, field emergence, yield, and thousand seed weight in comparison with the control.     

Evaluation of <Emphasis Type="Italic">Streptomyces</Emphasis> spp. for biological control of <Emphasis Type="Italic">Sclerotium</Emphasis> root and stem rot and <Emphasis Type="Italic">Ralstonia</Emphasis> wilt of chili pepper

The objective of this study was to screen Streptomyces spp. for biological control of root and stem rot (Sclerotium rolfsii) and bacterial wilt (Ralstonia solanacearum), the very destructive diseases of chili pepper in Thailand. About 265 isolates of Streptomyces spp. were tested for their inhibitory effects on S. rolfsii mycelial growth on dual culture plates. Then, 14 promising isolates were further tested for their effects on R. solanacearum growth. Three effective isolates further identified as S. mycarofaciens SS-2-243, S.philanthi RL-1-178 and S. philanthi RM-1-138 were selected and proved to produce both antifungal and antibacterial substances in the culture medium. S. philanthi RM-1-138 strongly inhibited seed germination and seedling growth of chili pepper in laboratory tests. Therefore, it was not used in the following studies. When tested in greenhouse conditions, the efficacy of S. philanthi RL-1-178 in suppressing Sclerotium root and stem rot of chili pepper was approximately equal to that of Trichoderma harzianum NR-1-52 or that of carboxin treatment. S. mycarofaciens SS-2-243 and S. philanthi RL-1-178 suppressed Ralstonia wilt of chili pepper in a way that was similar to streptomycin sulfate treatment and it was observed that T. harzianum NR-1-52 had no effect on the bacterial wilt. Under field conditions where the soil was inoculated with two pathogens, the results showed that S. philanthi RL-1-178 could protect the chili pepper plants from S. rolfsii and R. solanacearum infection better than S. mycarofaciens SS-2-243 or T. harzianum NR-1-52. S. philanthi RL-1-178 treatment resulted in 58.75% survival of chili pepper plants and its efficacy was not significantly different from the carboxin-and-streptomycin sulfate treatment.     

Evaluation of seed dressing and soil application formulations of Trichoderma species for integrated management of dry root rot of chickpea

The efficacy of the newly developed seed dressing and soil application formulations of Trichoderma viride, T. virens and T. harzianum were evaluated individually and in combinations under pot and field experiments for the management of dry root rot (Rhizoctonia bataticola) of chickpea (Cicer arientinum). In pot experiments, T. harzianum based seed dressing formulation, Pusa 5SD, and soil application formulations, Pusa Biogranule 5 (PBG 5) and Pusa Biopellet 10G (PBP 10G), were found to be effective in reducing dry root rot incidence in chickpea and increasing the seed germination, shoot and root lengths of the crop. Under field experiments, a combination of soil application of T. harzianum based PBP 10G and seed treatment with Pusa 5SD+carboxin was found to be the best by providing the highest seed germination, shoot and root lengths and grain yield and the lowest dry root rot incidence in chickpea.     

<Emphasis Type="Italic">Trichoderma harzianum</Emphasis>: a biocontrol agent against <Emphasis Type="Italic">Bipolaris oryzae</Emphasis>

Rice brown spot, caused by Bipolaris oryzae, can be a serious disease causing a considerable yield loss. Trichoderma harzianum is an effective biocontrol agent for a number of plant fungal diseases. Thus, this research was carried out to investigate the mechanisms of action by which T. harzianum antagonizes Bipolaris oryzae in vitro, and the efficacy of spray application of a spore suspension of T. harzianum for control of rice brown spot disease under field conditions. In vitro, the antagonistic behavior of T. harzianum resulted in the overgrowth of B. oryzae by T. harzianum, while the␣antifungal metabolites of T.␣harzianum completely prevented the linear growth of B. oryzae. Light and scanning electron microscope (SEM) observations showed no evidence that mycoparasitism contributed to the aggressive nature of the tested isolate of T. harzianum against B. oryzae. Under field conditions, spraying of a spore suspension of T. harzianum at 10⁸ spore ml⁻¹ significantly reduced the disease severity (DS) and disease incidence (DI) on the plant leaves, and also significantly increased the grain yield, total grain carbohydrate, and protein, and led to a significant increase in the total photosynthetic pigments (chlorophyll a and b and carotenoids) in rice leaves.     

Evaluation of Trichoderma harzianum strain T22 as biological control agent of Calonectria pauciramosa

The objective of this research was to evaluate Trichoderma harzianum strain T22 as a biocontrol agent of collar and root rot caused by different Calonectria pauciramosa isolates. Thus, the microsclerotia-forming ability and virulence of twenty C. pauciramosa isolates were assessed. Microsclerotia production varied partially among the isolates and dual culture with T22 on carnation leaf agar revealed isolates with both high and low microsclerotia-forming ability. Inoculation tests on red clover (Triflolium pratense) demonstrated its susceptibility to the pathogen. On red clover, the degree of virulence and T22 effects in controlling infections were highly variable among the isolates tested. A nursery trial performed on Feijoa sellowiana seedlings confirmed previous results, clearly indicating virulence variability among C. pauciramosa isolates. For three isolates tested in nursery trial, T22 effectiveness in controlling infection was inversely related to their degree of virulence. Overall, T. harzianum strain T22 showed good antagonist activity in reducing microsclerotia production on carnation leaf and the incidence and severity of collar and root rot on both selected hosts. This data could be crucial in developing integrated pest management strategies in ornamental plant nurseries.