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.     

Association of cucumovirus and potyvirus with betelvine (Piper betle L.) as evidenced by ELISA and RT-PCR

An attempt was made to detect various viruses of Piper betle grown at Mahoba and Banthara in India. DAC-ELISA and RT-PCR tests were performed in leaf sap samples of betelvine for detection of a cucumovirus (Cucumber mosaic virus) and potyvirus (Bean yellow mosaic virus) using specific antibodies and universal primers of respective viruses. DAC-ELISA could detect only CMV. However, RT-PCR detected both cucumovirus and potyvirus infection in betelvine samples. Association of CMV with betelvine was observed for the first time in the present study.     

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.     

The occurrence of sclerotium rot on Momordica charantia caused by Sclerotium rolfsii in Korea

Sclerotium rolfsii is one of the most destructive pathogens and thought to affect a broad range of plant hosts. In July 2014, an occurrence of sclerotium rot was observed on bitter melon (Momordica charantia L.) in Jinju, South Korea. The rot symptoms were most developed on stems and fruit near the soil line, and infected bitter melon plants withered and eventually died. White mycelial mats with numerous sclerotia were produced on diseased stems and fruit near the soil surface. Based on the morphological characteristics, pathogenicity tests, and DNA sequencing and phylogenetic analysis of the internal transcribed spacer (ITS) ribosomal RNA (rRNA) gene region, the causal fungus was identified as S. rolfsii Saccardo. This is the first report of sclerotium rot caused by S. rolfsii on bitter melon in Korea. The recent occurrence of sclerotium rot on bitter melon poses a potential threat to its production in Korea.     

Biocontrol of wilt disease complex of pea using Pseudomonas fluorescens and Rhizobium sp.

Biocontrol of wilt disease complex of pea caused by the root-knot nematode Meloidogyne incognita and Fusarium oxysporum f. sp. pisi was studied on pea (Pisum sativum L.) using plant growth-promoting rhizobacterium Pseudomonas fluorescens and root nodule bacterium Rhizobium sp. Inoculation of M. incognita and F.oxysporum alone caused significant reductions in plant growth over un-inoculated control. Reduction in plant growth caused by M. incognita was statistically equal to that caused by F. oxysporum. Inoculation of M. incognita plus F. oxysporum together caused a greater reduction in plant growth than the sum of damage caused by these pathogens singly. Inoculation of P. fluorescens and Rhizobium sp. individually or both together increased plant growth in pathogen inoculated and un-inoculated plants. Inoculation of P. fluorescens to pathogen-inoculated plants caused a greater increase in plant growth than caused by Rhizobium sp. Application of Rhizobium plus P. fluorescens caused a greater increase in plant growth than caused by each of them singly. Inoculation of P.fluorescens caused higher reduction in galling and nematode multiplication than caused by Rhizobium sp. Use of Rhizobium plus P. fluorescens caused higher reduction in galling and nematode multiplication than their individual inoculation. Plants inoculated with both pathogens plus Rhizobium showed less nodulation than plants inoculated with single pathogen plus Rhizobium. Inoculation of Rhizobium plus P. fluorescens resulted in higher root-nodulation than inoculated only with Rhizobium. Wilting indices were 4 and 5, respectively, when plants were inoculated with F. oxysporum and F. oxysporum plus M. incognita. Wilting indices were reduced maximum to 1 and 2, respectively, when plants inoculated with F.oxysporum and plants with both pathogens were treated with P. fluorescens plus Rhizobium.     

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.     

Biocontrol of Collar Rot Disease of Betelvine ( Piper betle L.) Caused by Sclerotium rolfsii by Using Rhizosphere-Competent Pseudomonas fluorescens NBRI-N6 and P. fluorescens NBRI-N

Collar rot disease of betelvine (Piper betle L.) caused by Sclerotium rolfsii is difficult to control by conventional means by use of chemicals; therefore, use of biocontrol agents is desirable. In the present study, 186 bacterial strains of different morphological types were screened for their biocontrol activity against S. rolfsii under in vitro conditions. Two strains, Pseudomonas fluorescens NBRI-N6 and P. fluorescens NBRI-N, were selected for further studies because of their ability to inhibit the mycelial growth of the pathogen significantly. Spontaneous rifampicin-resistant (Rif^r) derivatives of P. fluorescens NBRI-N6 and P. fluorescens NBRI-N showing growth rate and membrane protein composition comparable to the wild type were selected to facilitate their monitoring in the rhizosphere. Field trials demonstrated that strain P. fluorescens NBRI-N6 was better than P. fluorescens NBRI-N in increasing the yield of betelvine significantly, whereas a consortium of the two strains controlled the disease more than either of the strains. The screening method should prove useful in identifying rhizosphere bacteria with the greatest potential for controlling diseases caused by phytopathogenic fungi. RID= ID= <E5>Correspondence to:</E5> C.S. Nautiyal; <E5>email:</E5> nautiyalnbri&commat;yahoo.com Received: 5 August 2002 / Accepted: 7 October 2002     

Role of Petiole in Protein Metabolism of Senescing Betel (Piper betle L.) Leaves

Effects of depetiolation on protein metabolism during senescence of detached betel (Piper betle L.) leaves have been studied. In normal petiolated leaves, the level of chlorophyll and proteins and extent of protein synthesis declined, while the protease activity registered manifold increase with the advancement of senescence. All of these changes were delayed by depetiolation/de-midribbing treatments, though without affecting the general pattern of senescence. Thus, the presence of petiole seems to expedite protein degradation, probably due to earlier attainment of optimal concentration of proposed senescence factor(s) (Mishra and Gaur 1970 Science 167: 387).     

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.     

The effects of inoculum density and physical factors on the assessment of disease caused by Sclerotium rolfsii

Greenhouse and laboratory experiments were conducted to determine the effects of various physical factors on the assessment of disease caused by Sclerotium rolfsii using field and artificially infested soils. Lentil(Lens esculenta Moench) seedlings growing in trays or pots with sand were inoculated by surrounding them with a layer of soil infested with the pathogen. The number of dead plants was maximal within a 10-day period following inoculation. Seedling mortality increased with the number of sclerotia in the soil to a maximum that depended on seedling spacing, depth of the soil layer, and soil type.     

Biocontrol of Phytophthora cactorum the causal agent of root and crown rot on apple (Malus domestica) by formulated Pseudomonas fluorescens

In this study 284 isolates were isolated of apple trees' rhizosphere from Iran and 128 isolates were obtained from the collection of Research Department of Biological Control of University of Tehran. Four strains (P60, P61, P96, and P97) of Pseudomonas fluorescens were selected for greenhouse trials. The results of greenhouse trials showed dipping the crown and root of apple seedlings (MM106) combined with soil drench was more effective than dipping the crown and root on reducing the disease. After 6 weeks, strain P60 in dipping method combined with soil drench with 70% control, exhibited greatest effect on reducing the crown and root rot and was more effective than the fungicide metalaxyl-mancozeb. After 12 weeks, strains P60 and P96 in dipping method combined with soil drench with 55.6% and 44.5% control respectively, exhibited greatest effects on reducing the diseases Study of media on growth rate populations of effective strains exhibited that the beet molasses yeast extract (1:1) had more effect than nutrient broth(NB) medium. The initial high populations of powder formulations of strains P60 and P96 decreased during the storage at 4 and 25 degrees C over a 150-day period. In addition, formulations of strains stored at 4 degrees C had longer shelf life than those stored at 25 degrees C. In glasshouse trials, after 6 weeks, formulation of strain P60 and unformulated P60, obtained from NB medium and formulated P60, obtained from molasses yeast extract medium, and metalaxyl-mancozeb had highest effect on reducing the disease on apple rootstocks. After 12 weeks, formulation of strain P60 and unformulated bacteria obtained from both media, and metalaxyl-mancozeb with 57.1% control showed greatest effect on reducing the disease.     

Evidences of biological control capacities of Streptomyces spp. against Sclerotium rolfsii responsible for damping-off disease in sugar beet (Beta vulgaris L.)

Ten antibiotic-producing Streptomyces spp. isolated from Moroccan soils were evaluated for their ability to inhibit in vitro Sclerotium rolfsii development. Four isolates having the greatest pathogen inhibitory capabilities were subsequently tested for their ability to inhibit sclerotial germination in sterile soil. This test was carried out by using biomass inoculum, culture filtrate, and spore suspension of the isolates as treatment. Treatment with biomass inoculum and culture filtrate gave the highest inhibition of sclerotia. Biological control tests against Sclerotium rolfsii damping-off of sugar beet seeds showed that the selected Streptomyces isolates reduced significantly the disease severity, the J-2 isolate being the more potent. In addition, treatment with the isolate J-2 resulted in a significant increase (P ≤ 0.05) in seedling development compared to the control. All antagonistic Streptomyces selected here were able to grow in the rhizosphere soil from infected sugar beet culture.     

Possibility of using a bacterial antagonist against fungal diseases of Piper betle L. and corchorus spp.

Summary A strain ofBacillus subtilis isolated from soil was found effective againstSclerotium rolfsii when grown on 20% potato extract for 48 hours and used along with the medium. Whole boiled potato was also a good medium but the bacteria needed 20 days to grow until insoluble starch was digested.In field trials the antagonist brought down the spread ofSclerotium and anthracnose diseases ofPiper betle. Against seed and air-borne diseases of jute caused byMacrophomina phaseoli,Diplodia corchori andColletotrichum corchori, the antagonist also showed promising results.Concluding part of a scheme supported by Food & Agriculture Council, Pakistan.     

Induction of Systemic Acquired Resistance in Arachis hypogaea L. by Sclerotium rolfsii Derived Elicitors

Plants evolve a strategy to survive the attacks of potential pathogens by inducing the microbial signal molecules. In this study, plant defence responses were induced in four different varieties of Arachis hypogaea (J‐11, GG‐20, TG‐26 and TPG41) using the fungal components of Sclerotium rolfsii in the form of fungal culture filtrate (FCF) and mycelial cell wall (MCW), and the levels of defence‐related signal molecule salicylic acid (SA), marker enzymes such as peroxidase (POX), phenylalanine ammonia lyase (PAL), β‐1,3‐glucanase and lignin were determined. There was a substantial fold increase in POX, PAL, SA, β‐1,3‐glucanase and lignin content in FCF‐ and MCW‐treated plants of all varieties of groundnut when compared to that of control plants. The enzyme activities were much higher in FCF‐treated plants than in MCW‐treated plants. The increase in fold activity of enzymes and signal molecule varied between different varieties. These results indicate that the use of fungal components (FCF and MCW) had successfully induced systemic resistance in the four different varieties of groundnut plants against Sclerotium rolfsii.     

Phytohormone production and colonization of canola (Brassica napus L.) roots by Pseudomonas fluorescens 6-8 under gnotobiotic conditions

Pseudomonas fluorescens 6-8, a rhizosphere isolate previously shown to enhance root elongation of canola ( Brassica napus L.), was characterized for its ability to produce indole-3-acetic acid and cytokinins in pure culture and in the rhizosphere of canola under gnotobiotic conditions in comparison with the cytokinin-producing strain P. fluorescens G20-18 and its mutant CNT2. Strain 6-8 produced isopentenyl adenosine, zeatin riboside, and dihydroxyzeatin riboside at levels similar to those of G20-18, but only very low concentrations of indole-3-acetic acid. In a gnotobiotic assay canola inoculated with 6-8 and G20-18 had higher concentrations of isopentenyl adenosine and zeatin riboside in the rhizosphere and greater root length than the noninoculated control. The ability of strain 6-8 to colonize canola roots was assessed following transformation with the green fluorescent protein and inoculation onto canola seed in a gnotobiotic assay. Higher populations of strain 6-8 were observed on the proximal region of the root closest to the seed than on the mid and distal portions 9?days after seed inoculation. The ability of P. fluorescens 6-8 to produce cytokinins, colonize the roots of canola seedlings, and enhance root elongation may contribute to its ability to survive in the rhizosphere and may benefit seedling growth.     

Progesterone moderates damage in Arabidopsis thaliana caused by infection with Pseudomonas syringae or P. fluorescens

Brassinosteroids are known to protect plants against various abiotic and biotic stresses, however, very limited information is available about the role of progesterone. Therefore the effects of Pseudomonas syringae pv. syringae (P.s.) wild type strain 61, its hrcC mutant, and the saprophytic P. fluorescens (P.f.) strain 55 were investigated in wild type Arabidopsis thaliana cv. Columbia and its rbohF knock-out mutant, with and without progesterone pre-treatment. The reactions of wild type and rbohF mutant Arabidopsis to bacterial inoculations were similar, although 2 h after injection of P.s. a larger increase of electrolyte leakage was measured in wild type than in rbohF knockout mutant leaves. The hrcC mutant caused weak necrotic symptoms and increased leakage in both types of Arabidopsis, although to a much lesser extent than P.s. The P.f. did not induce any visible symptom, but slightly increased the electrolyte leakage in both types of Arabidopsis. Inoculation by all Pseudomonas bacteria led to significant alterations in photosystem 2 efficiency as compared to control plants. Pre-treatment of leaves with progesterone diminished the necrotic symptoms, the electrolyte leakage and improve the efficiency of photosystem 2 caused by Pseudomonas bacteria.