Induction of systemic resistance in pearl millet (Pennisetum glaucum) against downy mildew (Sclerospora graminicola) by Datura metel extract

A leaf extract of Datura metel protected pearl millet plants against downy mildew disease caused by Sclerospora graminicola. Of the different concentrations tested, the highest seed germination and seedling vigor was recorded when seeds were treated with a 2% extract for 3 h. When tested for induction of resistance against downy mildew disease, seed treatment with D. metel extract resulted in 79 and 67% protection under greenhouse and field conditions respectively. The resistance offered by D. metel extract was demonstrated to be systemic acquired resistance (SAR) and was active at both early and later stages of plant growth. An association between induction of resistance and salicylic acid (SA) content was drawn by quantifying the enhanced level of endogenous salicylic acid in root (4-fold) and shoot (10-fold) portions of induced seedlings. The highest levels of salicylic acid were observed in roots and shoots of highly resistant (HR) and SAR seedlings 3 and 6 h after inoculation respectively. The defense related enzymes, peroxidase, β-1,3-glucanase and chitinase, showed 1.5-2.6-fold increased activity in SAR seedlings. In addition to disease protection, plants with induced resistance showed 1.2-1.3-fold increased growth, in biomass, number of earheads and grain yield. Taken together, our results strongly suggest that seed treatment with D. metel extract provides protection against the downy mildew pathogen

Activity of cyazofamid against Sclerospora graminicola, a downy mildew disease of pearl millet

The efficacy of cyazofamid was tested against pearl millet downy mildew disease caused by Sclerospora graminicola Schroet. Significant inhibition of sporangial sporulation, zoospore release and motility was observed at 0.3 mg mL<SUP>−1</SUP>, and this concentration also provided good fungicidal activity under in vitro conditions. Under glasshouse conditions, none of the concentrations tested, either 0.01-2 mg mL<SUP>−1</SUP> as seed treatment or 1-10 mg mL<SUP>−1</SUP> by foliar application, was found to be phytotoxic. The effect of cyazofamid was tested by seed treatment alone, seed treatment followed by foliar application and foliar application alone. Seed treatment with cyazofamid offered only 19.7% disease control, but seed treatment followed by a single foliar application to diseased plants provided good control over disease, seed treatment with two foliar applications was significantly superior and foliar application alone showed a high level of activity, with 10 mg mL<SUP>−1</SUP> giving 97.9% disease control. Lack of systemic activity of cyazofamid was evident, root treatment giving disease levels on a par with the untreated control. The fungicide exhibited strong curative activity, but only moderate translaminar activity, with only marginal (34.8%) disease control after treatment of the adaxial leaf surface at 10 mg mL<SUP>−1</SUP>. Loss of cyazofamid activity over time was very low, indicating stable residual and rainfastness activity. These results indicate that cyazofamid has a high potential to be an effective fungicide for the control of downy mildew disease of pearl millet

Antisporulant activity of leaf extracts of Indian plants against Sclerospora graminicola causing downy mildew disease of pearl millet

Methanolic extracts of forty plant species commonly growing across India were collected and have been screened for antisporulant activity against Sclerospora graminicola (Sacc.) Schroet., the causative agent of pearl millet downy mildew. The collection represented 38 genera of 30 families. The methanolic extracts of nine species did not show any effect, whereas the activity of the extracts of Clematis gouriana, Evolvulus alsinoides, Mimusops elengi, Allium sativum and Piper nigrum were commensurable to that of the marketed botanical fungicides. The extracts of 11 species (Agave americana, Artemisia pallens, Citrus sinensis, Dalbergia latifolia, Helianthus annus, Murraya koenigii, Ocimum basilicum, Parthenium hysterophorus, Tagetes erecta, Thuja occidentalis and Zingiber offinale) exhibited remarkable antisporulant effect even after 10-fold dilution of the crude extracts while in the case of remaining 15 plants the crude extracts loosed activity after 10-fold dilution. The antisporulant activity of commercialised Azadirachta preparation (Nutri-Neem) was more pronounced than that of Reynutria based one (Milsana) and Sabadilla (veratrin), however, these botanical preparations held off the extracts of C. gouriana and E. alsinoides and synthetic fungicides

Elicitation of resistance and associated defense responses in trichoderma hamatum induced protection against pearl millet downy mildew pathogen

Endophytic Trichoderma hamatum UoM 13 isolated from pearl millet roots was evaluated for its efficiency to suppress downy mildew disease. Under laboratory conditions, T. hamatum seed treatment significantly enhanced pearl millet seed germination and seedling vigor. T. hamatum seed treatment resulted in systemic and durable immunity against pearl millet downy mildew disease under greenhouse and field conditions. T. hamatum treated seedlings responded to downy mildew infection with high lignification and callose deposition. Analysis of defense enzymes showed that T. hamatum treatment significantly enhanced the activities of glucanase, peroxidase, phenylalanine ammonia-lyase, and polyphenol oxidase in comparison to untreated control. RT-PCR analysis revealed differentially expressed transcripts of the defense enzymes and PR-proteins in treated, untreated, and checks, wherein PR-1, PR-5, and cell wall defense HRGPs were significantly over expressed in treated seedlings as against their lower expression in controls. T. hamatum treatment significantly stimulated endogenous salicylic acid ( SA) levels and significantly upregulated important SA biosynthesis gene isochorismate synthase. The results indicated that T. hamatum UoM13 treatment induces resistance corresponding to significant over expression of endogenous SA, important defense enzymes, PR-proteins, and HRGPs, suggesting that SA biosynthetic pathway is involved in pearl millet for mounting systemic immunity against downy mildew pathogen