Abstract: Penicillic acid was isolated from a culture filtrate of Aspergillus sclerotiorum.Ithadahigh in vitro antifungal activity against Phytophthora spp., which has not been previously reported. MICs of penicillic acid were from 1 to 25 µgml-1 against Phytophthora spp. Penicillic acid induced abnormal branch formation, apical branching, and swelling in P. capsici,in P. cactorum mycelia contained irregular branching and small spherical swelling at apices, in P. cambivora there was irregular branching and swelling, and in P. drechsleri there was irregular multiple spherical swelling at or near hyphal apices.
Abstract:Pseudomonas aureofaciens (c P. chlororaphis) strain 63-28 is a
biocontrol agent active against many soil-borne fungal plant pathogens and
shows antifungal activity in culture assays. 3-(1-Hexenyl)-5-methyl-2-(5H)fur-
anone was isolated from culture filtrates of this bacterium. The purified
furanone showed antifungal activity against Pythium ultimum, Fusarium
solani, Fusarium oxysporum, and Thielaviopsis basicola. The ED50S for spore germination of these fungi were 45, 54, 56, and 25 mg/ml,
respectively. The compound also inhibited the germ tube growth of
Rhizoctonia solani growing from microsclerotia, with an ED50 of 61 mg/ml.
The compound is the reduced form of furanones previously described
from this bacterium: 3-(1-hexenyl)-5-hydroxy-5-methyl-2-(5H)-furanone and
3-(1-hexenyl)-5-hydroxymethyl-2-(5H)-furanone. This volatile antifungal fur-
anone has structural similarity to other antifungal furanones produced by
actinomycetes (Streptomyces spp.), fungi (Trichoderma harzianum), and higher plants (Pulsatilla and Ranuculus spp.). This is the first report of 3-(1-hexenyl)-5-methyl-2-(5H)-furanone produced by a bacterium.
Abstract:Phytophthora blight is one of the most important devastating diseases of red pepper plants. Forty-one bacterial isolates were obtained from rhizosphere soil and subsequently tested for antagonistic activity under in vitro and in vivo conditions. Among the 41 isolates tested, 12 exhibited a maximum antagonistic activity in dual culture assay. These 12 isolates were further screened for disease suppression on red pepper plants in both natural and greenhouse conditions. All the antagonists showed varying levels of antagonism, whereas the isolates R33 and R13 exhibited the maximum (86.8 and 71%) ability to reduce the disease severity in in vivo conditions. Based on the 16S rDNA sequencing, the most effective isolates were identified as Bacillus subtilis. In addition, the isolates were also screened for siderophores, hydrogen cyanide and hydrolytic enzymes. Further, the isolates increased the root and shoot length of the red pepper, which is an added advantage of the isolates while performing the desired function.
Abstract: The effect of pepper seed and root treatments with Trichoderma harzianum spores on necrosis caused in stems by Phytophthora capsici inoculation and on the course of capsidiol accumulation in the inoculated sites were
studied. The results indicate that seed treatments significantly reduced stem necrosis, which fell by nearly a half compared with the values observed in plants grown from non-treated seeds. Necrosis was also reduced in plants
whose roots were drenched with various doses of T. harzianum spores, although the extent of necrosis was not correlated with the dose used. Attempted isolation of P. capsici and T. harzianum from the zones immediately contiguous with the necrotic zones revealed the presence of the former but not of the latter, suggesting that there was no direct contact between them in the zones of isolation, which means that there was no competition for space. The percentage of P. capsici isolated 9 days after inoculation was greater in non-treated inoculated plants than in treated inoculated plants. These results suggest that T. harzianum, introduced into the subterranean part of the plant, induces a systemic defense response against P. capsici in the upper part of the plant. Analysis of capsidiol in the stems of treated inoculated plants by the end of the sixth day after inoculation, revealed that its concentration was more than seven-fold greater than in non-treated and inoculated plants, while after 9 days, the concentration of capsidiol decreased in the treated inoculated plants and increased in the non-treated inoculated plants. The high concentration of capsidiol detected in treated and inoculated stems after 6 days might be one of
the contributing factors, but not necessarily the main factor, in delaying lesion development in the stems of pepper plants.
Abstract: Compost sustaining amultitude of chitinase-producing bacteria was evaluated
in a greenhouse study as a soil amendment for the control of late blight (Phytophthora capsici L.) in pepper (Capsicum annuum L.). Microbial population and exogenous enzyme activity were measured in the rhizosphere and correlated to the growth and health of pepper plant. Rice straw was composted with and without a chitin source, after having been inoculated with an aliquot of coastal area soil containing a known titer of chitinase-producing bacteria. P. capsici inoculated plants cultivated in chitin compost-amended soil exhibited significantly higher root and shoot weights and lower root mortality than plants grown in pathogen-inoculated control compost. Chitinase and b-1,3-glucanase activities in rhizosphere of plants grown in chitin compost-amended soil were twice that seen in soil amended with control compost. Colony forming units of chitinase-producing bacteria isolated from rhizosphere of plants grown in chitin compost-amended soil were 103 times as prevalent as bacteria in control compost. These results indicate that increasing the population of chitinase-producing bacteria and soil enzyme activities in rhizosphere by compost amendment could alleviate pathogenic effects of P. capsici.
Abstract: The potential of biocontrol products and plant extracts for control of late blight on potato plants, caused by Phytophthora infestans was evaluated in detached leaf assays and on potted plants. Based on an initial screening of 22 preparations and plant extracts, the 10 most active treatments were selected for further investigation. In the detached leaf assays the commercial preparations Elot-Vis, Serenade and Trichodex,and plant extracts of Rheum rhabarbarum and Solidago canadensis showed a significant effect on the level of infestation by P. infestans. However, none of the treatments was as effective as copper. In the case of Serenade, the metabolites produced by its active micro-organism, Bacillus subtilis, were demonstrated to be
the effective component of the formulation, and not the micro-organism itself. In order to take curative and protective modes of action into account, the test substances were applied 24 h before, or 90 min after inoculation with P. infestans. Generally, better effects were obtained when the applications were made 24 h before inoculation. For defining the optimum time of application, potted plants were treated 72 or 24 h before, and 1 and 24 h after inoculation with P. infestans. In these tests, Trichodex showed no activity, while Elot-Vis gave best results when applied 1 day before inoculation. Serenade and the extracts of R. rhabarbarum and S. canadensis (all at 5% concentration) however, were effective when applied up to 3 days before and just after inoculation with P. infestans. The results of the experiments on potted plants indicated direct effects on the pathogen for all agents except the extract of S. canadensis, but other mode of actions, e.g. induced resistance, could not be ruled out. None of the treatments had a curative effect.
Abstract:Phytophthora blight of pepper caused by Phytophthora capsici has devastating consequences when combined with other pathogens, including Rhi-
zoctonia solani, Fusarium oxysporum,and Fusarium solani. In order to develop a field-effective biocontrol strategy against Phytophthora blight of pepper, three chitinolytic bacteria, Serratia plymuthica strain C-1, strongly antagonistic to P. capsici, Chromobacterium sp. strain C-61, strongly antagonistic to R. solani,and Lysobacter enzymogenes strain C-3, antagonistic to R.
solani and Fusarium spp., were selected. In pot studies, application of cultures combining the three bacterial strains effectively suppressed Phytophthora blight more than application of any single bacterial strain. Bioformulations developed from growth of the strains in a simple medium containing chitin under large batch conditions resulted in effective control in field applications. Efficacy of the bioformulated product depended on both the dose and timing of application. Although the undiluted product suppressed Phytophthora blight under all field conditions, a 10-fold diluted product was effective in solar-sterilized greenhouses and in fields with crop rotation. These results suggest that the developed product could be a new effective system to control Phytophthora blight disease in pepper.
Abstract:Trichoderma harzianum isolate T39 and T. virens isolate DAR 74290 were evaluated as potential biological agents for control of pink rot of potato and root and stem rot of tomato caused by Phytophthora erythroseptica. Cell-free metabolites of T. virens DAR 74290 completely inhibited growth of P. erythroseptica in vitro and appeared to be fungicidal. T. virens DAR 74290 and Trichodex, a commercial formulation of T. harzianum T39, were tested for their ability to protect potato and tomato plants from disease caused by P. erythroseptica in glasshouse experiments. Trichodex and T. virens DAR 74290, alone and combined, reduced disease severity in shoots and roots of potatoes 10 weeks after inoculation with the pathogen. The yield of potatoes from plants treated with P. erythroseptica and T. virens DAR 74290 (mean of 12.9 g fresh weight/pot) was significantly greater than in controls inoculated with the pathogen alone (mean of 2.1 g/pot). Treatment with Trichodex alone increased the yield of tubers compared to the uninoculated controls. T. virens DAR 74290 increased the survival of tomato seedlings inoculated with the pathogen, and both this isolate and Trichodex decreased the severity of disease on tomato.
Abstract: To evaluate the biocontrol effectiveness of chitinase-producing bacterium,
Paenibacillus illinoisensis strain KJA-424 against pathogenic strain of Phytophthora capsici in pepper plants, growth response and kinetics of pathogen related (PR) proteins were estimated after inoculation with P. capsici (P), and with a combination of P. capsici and strain KJA-424 cell culture (P+A). Fresh weight and chlorophyll content in shoots at P+A-treated plants significantly increased by 23.4 and 34.2%, respectively after
7 days of inoculation, compared to P-treated plants. Root mortality in P+A-treated plants was significantly reduced compared to P-treated plants. Seven days after inoculation, the activities of b-1,3-glucanase, cellulase and chitinase in P-treated roots had decreased by 54.8, 36.5 and 52.8%, respectively, compared to P+A-treated roots, while those in P-treated leaves increased by 22.8, 36.3 and 23.8%, respectively, compared to those in P+A-treated leaves. The activities of b-1,3-glucanase, cellulase and chitinase in roots are negatively correlated with root mortality. All these results suggest that the inoculation of an antagonist, P. illinoisensis alleviates root mortality, reduction of PR proteins in roots, and activates of PR proteins in leaves infected by P. capsici.
Abstract: Mycological analysis throughout the vegetation period of potato(Solanum tuberosum) made it possible to study in detail the structure of the micromycete community, to determine typical dominant (frequency,more than 60%), typical common (frequency, 30 to 60%), typical rare (frequency, 10 to 30%), and casual (frequency, less than 10%) species and to estimate changes in the microorganism community caused by plant protection preparations with different mechanisms of action. It was shown that, as a result of occurrence of resistant forms, synthetic preparations against fungal pathogens of potato (such as TMTD,Ridomil gold MC, and Cupricol) were only slightly more effective than biological preparations (Trichodermin and AgroChit), with the former considerably changing the natural saprophytic mycological community. An increase in the soil pool of Trichoderma harzianum as a result of application of a biological preparation based on this antagonistic fungus correlated with its effectiveness against the soil pathogen Fusarium sp., which causes root rot. A chitosan-based elicitor preparation more effectively suppressed the development of early (Alternaria sp. and Macrosporium sp.) and late (Phytophthora sp.) blighting of leaves and had a weaker effect on soil microflora.
Abstract