K. Seetharaman

Advances in genetically engineered (transgenic) plants in pest management—an over view

Abstract Transgenic plants are produced via Agrobacterium mediated transformation and other direct DNA transfer methods. A number of transgenes conferring resistance to insects, diseases and herbicide tolerance have been transferred into crop plants from a wide range of plant and bacterial systems. In the majority of the cases, the genes showing expression in transgenic plants are stably inherited into the progeny without detrimental effects on the recipient plant. More interestingly, transgenic plants under field conditions have also maintained increased levels of insect resistance. Now, transgenic crops occupy 44.2 million hectares on global basis. During the last 15 years, transformations have been produced in more than 100 plant species; notable examples include maize, wheat, soybean, tomato, potato, cotton, rice, etc. Amongst these herbicide tolerant and insect tolerant cotton, maize and soybean carrying Bacillus thuringiensis ( Bt ) genes are grown on a commercial scale. Genetic transformation and gene transfer are routine in many laboratories. However, isolation of useful genes and their expression to the desired level to control insect pests still involves considerable experimentation and resources. Developing pest resistant varieties by insertion of a few or single specific gene(s) is becoming an important component of breeding. Use of endotoxin genes such as Bt and plant derived genes (proteinase inhibitors) to the desired levels offers new opportunities to control insects and strategies involving combination of genes. Transgenic technology should be integrated in a total system approach for ecologically friendly and sustainable pest management. Issues related to Intellectual property rights, regulatory concerns, and public perceptions for release of transgenics need to be considered. Providing wealth of information on gene expression in higher plants by switching the gene on and off as and when required, makes gene manipulation a more direct process for genetic improvement of crops.

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.

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.

Host range of Alternaria alternata—a potential fungal biocontrol agents for waterhyacinth in India

Abstract The host ranges of Alternaria alternata and fungi native to India and pathogen of waterhyacinth (Eichhornia crassipes) were evaluated using 29 plant species (some with several cultivars tested) representing 18 families of economic and ecological importance. The results showed that only waterlettuce (Pistia stratiotes), another common weed in India, was infected by A. alternata. The use of these pathogens in the biological control of waterhyacinth would not be expected to affect plants of economic and ecological importance in India.

Alternaria alternata toxin detection by fluorescence derivatization and separation by high performance liquid chromatography

An improved high performance liquid chromatographic (HPLC) method was developed for the detection and quantitation of host-specific AA-toxin produced byAlternaria alternata, a water hyacinth pathogen. Precolumn derivatization of the toxin witho-phthalaldehyde (OPA) plus mercaptoethanol yielded highly fluorescent products showing well resolved peaks on reverse-phase HPLC. The minimum amounts of AA-toxins detectable by this method were approximately 1 ng. This method seems to offer advantages over conventional techniques, because prechromatographic derivatization of the toxin with OPA is rapid and easy, and fluorescent derivatives permit excellent detection sensitivity. Toxin production in culture filtrates and spore-germinated fluids of the pathogen were analyzed quantitatively using this procedure.