H. Shekar Shetty

Roles of reactive oxygen species in interactions between plants and pathogens

The production of reactive oxygen species (ROS) by the consumption of molecular oxygen during host–pathogen interactions is termed the oxidative burst. The most important ROS are singlet oxygen (1O2), the hydroxyperoxyl radical (HO2·), the superoxide anion

Improvement of seed quality and field emergence of Fusarium moniliforme infected sorghum seeds using biological agents

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Biocontrol of downy mildew disease of pearl millet using Pseudomonas fluorescens

, hydrogen peroxide (H2O2), the hydroxyl radical (OH-) and the closely related reactive nitrogen species, nitric oxide (NO). These ROS are highly reactive, and therefore toxic, and participate in several important processes related to defence and infection. Furthermore, ROS also play important roles in plant biology both as toxic by-products of aerobic metabolism and as key regulators of growth, development and defence pathways. In this review, we will assess the different roles of ROS in host–pathogen interactions with special emphasis on fungal and Oomycete pathogens.

Chitosan enhances disease resistance in pearl millet against downy mildew caused by Sclerospora graminicola and defence-related enzyme activation.

One hundred and ninety seven maize samples representing different cultivars, collected from different agroclimatic regions of Karnataka (India) were analysed for moisture content, mould incidence, ergosterol and extent of mycotoxin contamination. Moisture content determination by the hot-air oven method revealed significantly high levels of moisture content (15-18%) in 34 (17%) samples, which exceeded the permissible limit for safe storage. Ergosterol quantification by HPLC revealed the presence of ergosterol in many samples collected from rural areas of Karnataka irrespective of the moisture content. Mould enumeration based on blotter and agar plating methods revealed the association of 24 diverse species of both field and storage moulds belonging to 14 genera. Mycotoxins analyses using monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) and thin-layer chromatography (TLC) revealed mycotoxin contamination in 69 (34.8%) samples. Maize samples with a high incidence of diverse species of moulds and alarmingly high levels of mycotoxins in many samples indicate the need for proper surveillance and monitoring exclusively for the prevention of moulds and mycotoxins in maize produce in Karnataka before it reaches the consumer.

Purification and properties of a major isoform of β-1,3-glucanase from pearl millet seedlings

Five different cultivars of sorghum seeds infected with a varied degree of Fusarium moniliforme were treated with biocontrol agents. Pure cultures of Pseudomonas fluorescens, Trichoderma harzianum and Chaetomium globosum at the rate of 1 x 10(8) cfu g(-1) and talcum based formulations of (28 x 10(7) cfu g(-1)), (19 x 10(7) cfu g(-1)) and (4 x 10(6) cfu g(-1)) at the rate of 6 g kg(-1) and 10 g kg(-1) of seeds were used, respectively. The treated seeds were evaluated for per cent reduction of F moniliforme, seed germination, vigour index and field emergence. It was found that the pure culture of P fluorescens was more effective in reducing the F moniliforme infection followed by T harzianum and C globosum than the Bavistin treated and untreated seeds. Formulations of P fluorescens were effective in reducing the F moniliforme infection and also in increasing the seed germination, vigour index and field emergence, followed by T harzianum and C globosum treatments in comparison with control

Thiamine seed treatment enhances LOX expression, promotes growth and induces downy mildew disease resistance in pearl millet

Differential resistance of pearl millet cultivars to downy mildew disease was correlated with the levels of β-1,3-glucanase in their seeds. Higher activity of the enzyme in highly resistant cultivars and lower activity in the highly susceptible ones suggested the possible use of β-1,3-glucanase as a biochemical marker for screening pearl millet cultivars for downy mildew disease. Inoculation of seedlings with the downy mildew pathogen Sclerospora graminicola resulted in increased enzyme levels in resistant cultivars. Mesocotyl and shoot regions of seedlings recorded higher levels of enzyme than the root. Isoelectric focusing revealed four basic isoforms with pI 9.6, 9.0, 8.9 and 8.2 and two acidic isoforms with pI 4.9 and 6.2 of β-1,3-glucanase in pearl millet. The pI 9.6 isoform was a major isoform of the enzyme in the pearl millet seedlings with a probable developmental function. Isoforms pI 6.2 and pI 8.2 appeared to be involved in resistance and pI 4.9 isoform seemed to be involved in pathogenesis of pearl millet-downy mildew.

Pathogenesis Related Proteins in Plant Defense Response

Pseudomonas fluorescens was tested against pearl millet downy mildew disease by treating seeds with a pure culture and formulated in talc powder. The bioagent was also tested as a foliar spray to pearl millet under greenhouse and field conditions. Treated seeds increased seedling vigour and inhibited sporulation of downy mildew pathogen. P. fluorescens controlled downy mildew disease both by seed treatment and foliar application, but efficacy was significantly higher when seed treatment was followed by a foliar application. Seed treatment was better than foliar application alone.

Infection processes of Sclerospora graminicola on Pennisetum glaucum lines resistant and susceptible to downy mildew

BACKGROUND The present study investigated the effect of chitosan seed priming on the induction of disease resistance in pearl millet against downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroet. RESULTS Pearl millet seeds were primed with chitosan at different concentrations: 0.5, 1.5, 2.5 and 3 g kg(-1) seed. Of the different concentrations, 2.5 g kg(-1) was found to be optimum, with enhanced seed germination of 99% and seedling vigour of 1782, whereas the untreated control recorded values of 87% and 1465 respectively. At optimum concentration, chitosan did not inhibit sporulation and release of zoospores from sporangia. Furthermore, pearl millet seedlings raised after seed treatment with chitosan showed an increased level of the defence-related enzymes chitosanase and peroxidase as compared with the untreated pearl millet seedlings on downy mildew pathogen inoculation. The effect of chitosan in reducing downy mildew incidence was evaluated in both greenhouse and field conditions, in which respectively 79.08 and 75.8% disease protection was obtained. CONCLUSION Chitosan was effective in protecting pearl millet plants against downy mildew under both greenhouse and field conditions by inducing resistance against the pathogen. Thus, chitosan formulation can be recommended for seed treatment in the management of downy mildew disease.