P. Vidhyasekaran

Induction of systemic resistance byPseudomonas fluorescens Pf1 againstXanthomonas oryzae pv.Oryzae in rice leaves

When lower leaves of rice plants were inoculated with powder formulation of a saprophytic strain ofPseudomonas fluorescens, Pfl, upper leaves, in addition to the inoculated lower leaves, showed resistance to the rice bacterial blight pathogenXanthomonas oryzae pv.oryzae. When the leaves were challenge-inoculated withX. oryzae pv.oryzae 4 days afterP. fluorescens application on lower leaves, the disease intensity in upper leaves decreased from 6.7 to 1.1. When rice seeds were treated with the formulation ofP. fluorescens Pfl and sown, 30-day-old seedlings showed resistance toX. oryzae pv.oryzae and the disease intensity decreased from 6.8 to 1.2. The induced resistance was transient; leaves sprayed withP. fluorescens Pfl at 30 days after treatment and leaves of 60-day-old seedlings fromP. fluorescens-treated seeds did not show resistance to the pathogen. In field trials, seed treatment followed by foliar application of the powder formulation ofP. fluorescens Pfl effectively controlled rice bacterial blight and increased the yield. In the induced resistant leaves a sharp increase in lignification and activities of peroxidase, phenylalanine ammonia-lyase and 4-coumarate: CoA ligase was observed when the leaves were challenge-inoculated withX. oryzae pv.oryzae. An approximately threefold increase in lignin content, peroxidase activity and phenylalanine ammonia-lyase activity and a fivefold increase in 4-coumarate: CoA ligase activity were observed 5 days after challenge inoculation withX. oryzae pv.oryzae in rice leaves pretreated withP. fluorescens for 5 days. A similar increase in defense-related activities was not observed in susceptible interactions or inP. fluorescens-treated plants at later stages of interactions when no resistance to the pathogen was observed.

Induction of pathogenesis-related proteins in sugarcane leaves and cell-cultures by a glycoprotein elicitor isolated from Colletotrichum falcatum

The induction of pathogenesis-related (PR) proteins in sugarcane (Saccharum officinarum L.) leaves and suspension-cultured cells in response to treatment with a glycoprotein elicitor isolated from Colletotrichum falcatum (the red rot pathogen) was investigated. Treatment of leaves and cells with the elicitor resulted in a much marked increase in the activities of chitinase and β-1,3-glucanase in red rot resistant (BO 91) than susceptible (CoC 671) sugarcane cultivar. SDS-PAGE analysis revealed that C. falcatum elicitor induced the accumulation of several proteins in suspension-cultured cells of resistant cultivar (BO 91); among them the 35 kDa protein was predominant. Whereas, a 27 kDa protein was induced predominantly in the cells of susceptible cultivar upon treatment with the elicitor. When sugarcane leaves were treated with C. falcatum elicitor, two proteins with apparent molecular masses of 25 and 27 kDa were induced both in the resistant and susceptible cultivars. However, the induction was stronger in the resistant than the susceptible cultivar. Immunoblot analysis for chitinase indicated that a protein with an apparent molecular mass of 37 kDa cross-reacting with barley chitinase antiserum was strongly induced in the suspension cultured cells of both the cultivars. The induction of 37 kDa chitinase was more in the cells of resistant cultivar than in the susceptible cultivar. Western blot analysis revealed that a 25 kDa thaumatin-like protein (TLP) cross-reacting with bean TLP antiserum was strongly induced in leaves and cultured cells of both resistant and susceptible cultivars due to elicitor treatment.

Purification of an elicitor-inducible antifungal chitinase from suspension-cultured rice cells.

Suspension-cultured rice cells showed an appreciable amount of chitinase activity when the cultured cells were treated with an elicitor isolated fromRhizoctonia solani, the rice sheath blight pathogen. A fivefold increase in chitinase activity was observed 24 h after elicitor treatment. The elicitor-inducible chitinase was purified by ammonium sulfate fractionation, chitin affinity chromatography and gel filtration. Its molecular weight is 35 kDa and it has an isoelectric point of 8.3. The 35 kDa basic chitinase inhibited mycelial growth ofR. solani in vitro. Morphological changes appeared within 1 h following exposure of mycelium to the chitinase. The hyphal tip showed marked swelling and subsequently lysis was also observed.

Induction of systemic resistance toColletotrichum falcatum in sugarcane by a synthetic signal molecule, acibenzolar-S-Methyl(CGA-245704)

The effect of a novel synthetic signal molecule, acibenzolar-S-methyl (CGA-245704; benzo [1,2,3] thiadiazole-7-carbothioic acid S-methyl ester), in inducing resistance in sugarcane against red rot disease caused by the fungusColletotrichum falcatum Went was studied. Application of CGA-245704 as a soil drench or along with marcotting rooting mixture induced resistance in sugarcane to challenge inoculation withC. falcatum. When the pathogen was inoculated by the plug method, it caused discoloration in the untreated control stalk tissues; however, in the stalk tissues pretreated with acibenzolar-S-methyl, pathogen colonization was considerably reduced. When the pathogen was inoculated by nodal swabbing, its penetration was arrested in the sensitized stalk tissues. An induced systemic resistance effect was found to persist up to 30 days in the pretreated cut canes. Increased phenolic content and accumulation of pathogenesis-related (PR) proteins,viz., chitinase, β-1,3-glucanase and thaumatin-like protein (PR-5), were observed in sugarcane plants treated with acibenzolar-S-methyl.

Induction of enzymatic scavengers of active oxygen species in rice in response to infection by Rhizoctonia solani

Changes in the activities of peroxidase, ascorbate peroxidase, catalase and superoxide dismutase in rice in response to infection by Rhizoctonia solani were studied. A significant increase in peroxidase activity was observed in R. solani-inoculated rice leaf sheaths 1 day after inoculation and the maximum enzyme activity was recorded 3 days after inoculation at which period a 3-fold increase in peroxidase activity was observed compared to the untreated control. Three peroxidase isozymes viz., PO-4, PO-5 and PO-6 were induced in rice upon infection by R. solani. Ascorbate peroxidase and catalase activities significantly increased 1–2 days after inoculation and the maximum enzyme activities were recorded 5 days after inoculation. Superoxide dismutase activity increased significantly 2 days after inoculation and increased progressively, reaching four times the control value at 7 days after inoculation.

Induction of systemic resistance to Xanthomonas oryzae pv. oryzae by salicylic acid in Oryza sativa (L.)

The effect of salicylic acid (SA) is hypothesized to be a natural signal that triggers the systemic induction of phenolics, pathogenesis-related proteins and disease resistance in rice against the bacterial leaf blight pathogen Xanthomonas oryzae pv. oryzae (Xoo). Rice plants pretreated with 1000 μmol/l Sa showed resistance to challenge inoculation with Xanthomonas oryzae pv. oryzae and the effectiveness persisted in the susceptible cv. ‘Ir 50’ for at least 3 days prior to inoculation with Xoo. To investigate the role of SA in rice disease resistance, we examined the endogenous levels of SA in the Sa-pretreated rice plants with Xoo inoculation. A three-fold increase in the endogenous Sa levels was observed in the rice tissues pretreated with 1000 μmol/l Sa and the resistance persisted for at least 3 days after Sa treatment prior to inoculation with Xoo. Increasing the endogenous level of Sa in rice leaves to those naturally observed during systemic acquired resistance resulted in increased resistance to Xanthomonas oryzae pv. oryzae, expressed as a reduction in leaf blight lesion length. Immunoblot analysis revealed an induction of a 25 kDa protein cross-reacting with rice thaumatin-like protein (TLP) antiserum in response to Sa-pretreated and Sa non-pretreated rice plants followed by pathogen inoculation. A significant increase in the induction of Tlps 3 days after Xoo inoculation in the tissues pretreated with Sa was observed when compared with the 2 days and 1 day after Xoo inoculation in SA-treated plants. Increased phenolics content and enhanced activities of some pathogenesis-related (PR) proteins, viz., TLP, chitinase and β-1,3-glucanase were observed in rice plants treated with SA. Based on these experiments, it was investigated that the defense responses are induced locally at the infection site only after pathogen attack and are augumented when the rice tissue has been pretreated with Sa. These data further support the hypothesis that the defense responses in rice can be rapidly triggered and induced in a genetically susceptible cultivar after treatment with SA.ZusammenfassungSalicylsäure (SA) soll ein natürliches Signal sein, das die systemische Induktion von phenolischen Verbindungen, Pr-Proteinen und Krankheitsresistenz in Reis gegen Xanthomonas oryzae pv. oryzae (Xoo), dem Erreger der Blattbräune, auslöst. Reispflanzen, die mit 1000 μmol/l SA vorbehandelt worden waren, zeigten Resistenz nach Inokulation mit X. oryzae pv. oryzae. Die Wirkung hielt in der anfälligen Sorte ‘Ir 50’ wenigstens 3 Tage vor der Inokulation mit Xoo an. Um die Rolle von Sa in der Krankheitsresistenz zu untersuchen, wurde der endogene Gehalt an Sa in den Geweben der mit Sa vorbehandelten Pflanzen nach Inokulation mit Xoo bestimmt. Eine dreifache Zunahme des endogenen Sa-Gehaltes in den mit 1000 μmol/l behandelten Reispflanzen wurde nachgewiesen. Die Resistenz dauerte wenigstens 3 Tage lang an vor Inokulation mit Xoo. Eine Erhöhung des endogenen Sagehaltes auf den unter natürlichen Bedingungen in Reisblättern beobachteten Gehalt während der systemisch induzierten Resistenz führte zu einer erhöhten Resistenz gegen X. oryzae pv. oryzae, gemessen an der Reduktion der Länge der Blattflecken. Durch Immunoblot-Analyse konnte die Induktion eines 25-kDa Proteins nachgewiesen warden, welches mit dem Thaumatin-ähnlichen rotein (TLP)- Antiserum von Reis kreuzreagierte als Reaktion auf Reispflanzen, die mit Sa vorbehandelt oder unbehandelt waren mit nachfolgender Xoo-Inokulation. Ein signifikanter Anstieg der Induktion von Tlps 3 Tage nach Inokulation mit Xoo in den mit SA vorbehandelten Geweben konnte im Vergleich zu den 2 Tage oder 1 Tag später inokulierten Pflanzen nachgewiesen warden. Erhöhte Gehalte an phenolischen Verbindungen und vermehrte Aktivitäten einiger PR-Proteine, nämlich Tlp, Chitinase und β-1,3-Glucanase wurden nach Behandlung von Reispflanzen mit Sa festgestellt. Auf der Basis dieser Ergebnisse kann gesagt werden, dass die Abwehrreaktionen lokal am Ort der Infektion nur nach Angriff des Pathogens induziert warden und dass sie verstärkt warden, wenn das Reisgewebe mit Sa vorbehandelt wird. Die Hypothese, dass Abwehrreaktionen in genetisch anfälligen Reissorten durch Behandlung mit Sa schnell ausgelöst und induziert warden können, wird durch die vorliegenden Daten unterstützt.

Characterization of a phytotoxic glycoprotein produced byPhoma eupyrena — A pathogen on water lettuce

Phoma eupyrena, the causal agent of leaf blight disease of water lettuce, when purified by affinity and ion exchange chromatography produced an extracellular glycoprotein (Pe 65) in concentrations of ∼ 8 µg ml−1 in the stationary culture. Coomassie-blue stained SDS-PAGE analysis of culture filtrates and purified Pe 65 showed its molecular mass to be 65 kDa. The blighting and necrosis of leaf tissues were observed within 4–6 days when 1–5 µg of Pe 65 was injected into the mesophyll of water lettuce. These symptoms closely resembled those caused by foliar inoculation with the pathogen. Recognition of Pe 65 by N-glycosidase F treatment and by polyclonal antibodies raised in rabbit against the whole glycoprotein, indicated that the protein is a highly glycosylated protein (50% carbohydrate) and that it is strongly enclosed by the antigenic glycosidic moiety.

Two pathogenesis-related peroxidases in greengram (Vigna radiata (L.) wilczek) leaves and cultured cells induced by Macrophomina phaseolina (Tassi) Goid. and its elicitor

An elicitor has been isolated from Macrophomina phaseolina, the root rot and leaf blight pathogen of greengram. Suspension-cultured cells of greengram were established which responded to the fungal elicitor. When greengram leaves were inoculated with M. phaseolina two new peroxidases appeared. Similarly, two new peroxidases could be detected in suspension-cultured greengram cells when treated with the fungal elicitor. These peroxidases were purified by column chromatography and their molecular masses were 27 and 38 kDa. The new peroxidases detected in both leaves and cultured cells appear to be similar with the same molecular weights.

RETRACTED: Advances in bioherbicides development—an overview

Abstract This paper is being retracted at the request of the Principal Editors. Reason: it was discovered after publication to include large sections that had been previously published by other authors in the following work: Biocontrol of weeds using pathogens: Recent advances, by Carol A. Ellison and Harry C. Evans, in the Proceedings of a Symposium on ‘Biocontrol Based Pest Management for Quality Crop Protection in the Current Millennium’, which was held at Punjab Agricultural University (PAU), Ludhiana, India on 18–19 July 2001 (pages 141–156). We very much regret this, and offer our apologies to the authorsconcerned.

A boll rot of cotton caused by Corynespora Cassiicola in Tamil Nadu, India

A new boll rot disease of cotton (Gossypium hirsutum L.) cv. MCU 9 was observed in Tamil Nadu, India, in 1988. The causal organism was isolated in pure culture and identified asCorynespora cassiicola (Berk. & Curt.) Wei. The isolate, which on cotton is pathogenic only to bolls, is considered to be different from a strain ofC. Cassiicola known elsewhere causing leaf spot of cotton. The pathogenicity of this fungus on several other important crops was also tested. The fungus produced leaf spot and stem rot diseases on, respectively, eight and six host plants. Root rot, after inoculation, was observed only inVigna sinensis, Arachis hypogaea andSesamum indicium.