Shantharaj Deepak

Nitric oxide is involved in chitosan-induced systemic resistance in pearl millet against downy mildew disease

BACKGROUND The nature and durability of resistance offered by chitosan and the involvement of nitric oxide (NO) in chitosan-induced defence reactions in pearl millet against downy mildew disease were investigated. RESULTS It had previously been reported that chitosan seed priming protected pearl millet plants against downy mildew disease. Further elucidation of the mechanism of resistance showed that chitosan seed priming protects the plants systemically. A minimum 4 day time gap is required between the chitosan treatment and pathogen inoculation for maximum resistance development, and it was found to be durable. Chitosan seed priming elevated NO accumulation in pearl millet seedlings, beginning from 2 h post-inoculation, and it was found to be involved in the activation of early defence reactions such as hypersensitive reaction, callose deposition and PR-1 protein expression. Pretreatment with NO scavenger C-PTIO and nitric oxide synthase (NOS) inhibitor L-NAME before pathogen inoculation reduced the disease-protecting ability of chitosan, and defence reactions were also downregulated, which indicated a possible role for NO in chitosan-induced resistance. CONCLUSION Protection offered by chitosan against pearl millet downy mildew disease is systemic in nature and durable. Chitosan-induced resistance is activated via NO signalling, as defence reactions induced by chitosan were downregulated under NO deficient conditions.

Seed treatment with aqueous extract of Viscum album induces resistance to pearl millet downy mildew pathogen

Abstract Downy mildew (Sclerospora graminicola [Sacc.] Schroet.) is a serious agricultural problem for pearl millet (Pennisetum glaucum [L.] R. Br.) grain production under field conditions. Six medicinally important plant species Azadirachta indica, Argemone mexicana, Commiphora caudata, Mentha piperita, Emblica officinalis and Viscum album were evaluated for their efficacy against pearl millet downy mildew. Seeds of pearl millet were treated with different concentrations of aqueous extract of the plants to examine their efficacy in controlling downy mildew. Among the plant extracts tested, V. album treatment was found to be more effective in enhancing seed quality parameters and also in inducing resistance against downy mildew disease. Germination and seedling vigor was improved in seeds treated with V. album extracts over control. Seeds treated with 10% concentration of V. album showed maximum protection against downy mildew disease under greenhouse and field conditions. The downy mildew disease protection varied from 44–70% with different concentrations. Leaf extract of V. album did not inhibit sporulation and zoospore release from sporangia of Sclerospora graminicola, indicating that the disease-controlling effect was attributed to induced resistance. Seed treatment with V. album extract increased pearl millet grain yield considerably. In V. album, treated pearl millet seedlings increased activities of peroxidase, and phenylalanine ammonia-lyase enzyme was detected. FTIR analysis of V. album extracts showed the presence of amides and other aromatic compounds which are antimicrobial compounds involved in plant defense.

Thionins (PR protein-13) mediate pearl millet downy mildew disease resistance.

Thionins (PR protein-13) are a class of Cys-rich polypeptides of about 5 kDa, and have revealed their role of the defense in pearl millet to Sclerospora graminicola. The purified 5 kDa thionins show a pI of 8.2 and have anti-mildew activity tested on S. graminicola. The high level of transcript expression of thionins in resistant compared to susceptible cultivars was observed. Immunofluorescence studies have shown intense fluorescence in epidermal regions, confirming its involvement in arresting pathogen ingress and in vascular regions, confirming its systemic translocation during interaction. Epidermal peeling of resistant cultivars showed that thionin protein was present in higher quantities at the papillar region of the cell wall in seedlings.

Response of pearl millet downy mildew (Sclerospora graminicola) to diverse fungicides

The inhibitory effect of 15 commercial and five experimental fungicides was assessed both in greenhouse and field experiments against Sclerospora graminicola, the causative agent of pearl millet downy mildew disease. Chemicals differed in anti-mildew activity. However, neither the pathogen nor the host plant was completely tolerant to any compounds tested. The plants depressed by fungicides in the germling stage recovered until formation of inflorescence, so this activity did not significantly influence grain yield. There was a significant correlation between antisporulant activity of compounds evaluated on detached leaf segments and their positive effect on yield performance. All compounds increased the grain yield of downy mildewed pearl millet when applied in the maximum doses tolerated by pearl millet. However, analysis of the cost-return budget showed that disease control < 30% is uneconomic. Fungicides of the acylanilide series exhibited the highest protective effect (over 95%) and andoprim, drazoxolon and efosit were also effective.

Serodiagnosis of pearl millet resistance to downy mildew by quantitating cell wall P/HRGP using polyclonal antiserum Pab-P/HRGP

Proline/hydroxyproline-rich glycoprotein (P/HRGP) level in pearl millet genotypes resistant to downy mildew increase after inoculation with the oomycete pathogen Sclerospora graminicola. Using purified P/HRGPs from pearl millet cell walls, polyclonal antibodies (Pab-P/HRGP) were raised in rabbit. Based on this antiserum, an enzyme immunoassay was developed that displays a linearity detection range from 0.01 to 10 μg P/HRGP. Western blot analysis, confirming the induction of three marker P/HRGPs in the infected resistant genotype, and immunocytochemical studies on P/HRGP localization either in epidermal peelings or in suspension-cultured cells demonstrated the specificity of the antiserum. Besides its characterization, Pab-P/HRGP was employed to screen various genotypes of pearl millet for fast, sensitive and specific detection of induced P/HRGPs upon infections. The results presented are discussed with presumed importance to downy mildew disease and the use of this new antiserum in pearl millet screening for disease resistance.