Rajkumar H. Garampalli

Antifungal activity of plants extracts against Alternaria solani, the causal agent of early blight of tomato

Aqueous extracts of 39 plants selected from local flora were evaluated for antifungal potential against Alternaria solani, causing early blight of tomato, at 4% concentration in Potato Dextrose Agar by poison food technique. Out of these, 13 plant extracts significantly reduced the mycelial growth of the pathogen, according to ANOVA, Tukey’s post-test. Inhibition rate of above 20% was shown by seven plant extracts namely Crotalaria trichotoma (36.6%), Citrus aurantifolia (27.3%), Azadirachta indica (23.7%), Polyalthia longifolia (23.3%), Datura metel (21.3%), Muntingia calabura (20.09%) and Oxalis latifolia (20.09%). At 2% concentration, six extracts showed significant growth inhibition namely, C. trichotoma (16.6%), A. indica (10%), Capsicum annum (7.1%), D. metel (6.6%), P. longifolia (6.3%) and C. aurantifolia (5.5%). The plant extracts shortlisted for pathogen inhibition have potential to be developed as potent fungicides in organic farming.

Evaluation of fungistatic potential of lichen extracts against Fusarium solani (Mart.) Sacc. causing Rhizome rot disease in Ginger

Eight lichens were collected, identified and solvent extract were obtained using methanol and ethyl acetate in soxhlet apparatus. Antifungal properties of lichens were determined by Agar well diffusion method, Microdilution assay and TLC- Bioautographic technique. The largest zone of inhibition in well diffusion method was recorded (in mm) with the ethyl acetate extract of Parmotrema tinctorum with 18.6±1.15 followed by Teloschistes flavicans with 18.6±0.5. The maximum antifungal activity was found in the extracts of lichen Parmotrema tinctorum and Flavoparmelia caperata with low MIC value of 1.562mg/ml. Flavoparmelia caperata extract was active with a clear zone on TLC bioautogram of the tested organism indicating two zones of growth inhibition at an Rf value of 0.46, 0.6. Comparatively ethyl acetate extract showed a strong antifungal activity than methanolic extract. The results were promising with potential drug candidate having a fungitoxic effect to reinforce bioprospecting of lichens as a bio-fungicide.

An efficient technique to obtain conidial inoculum of Peronosclerospora sorghi causing downy mildew of sorghum

An effective and simple technique to obtain conidial inoculum of Peronosclerospora sorghi has been devised, which confers many advantages over the conventional method. Systemically infected sorghum leaves were packed into folds of paper-towel. The end of folded paper-towel containing cut-ends of leaves was dipped in 3 cm deep water in a container. The container was exposed to moist field conditions at night and sporulated leaves were harvested with chilled distilled water in the morning to obtain the inoculum. Advantages of the technique include lower cost and effort, rapid harvesting and daily production of inoculum for up to seven consecutive days from same leaves. Though conventional method of plating leaf pieces in Petri plates proves superior in terms of the amount of sporulation, paper-towel method has the edge under working conditions.

Comparative evaluation of composts and dried powdered biomass of botanicals for organic management of downy mildew of sorghum

The biomass of 10 selected botanicals was evaluated as soil amendments, in the form of composts and dry powder biomass, to compare their potential to suppress downy mildew disease caused by oosporic inoculum of Perenosclerospora sorghi. Eight botanicals (Allium cepa, Lantana camara, Polyalthia longifolia, Hyptis suaveolens, Azadirachta indica, Nerium oleander Eucalyptus globulus and Tamarindus indica) proved effectively in the form of dry biomass powder at 4% (w/w) rate to control infection by oospores, while two (Croton sparsiflorus and Tagetes erecta) promoted it. In the form of composts (2% rate), the efficacy of botanicals was generally found reduced with the appearance of more disease than negative control in case of all botanicals except one (A. cepa). At the 4% compost rate, only four botanicals namely, A. cepa, P. longifolia, H. suaveolens and L. camara were found to suppress the disease. At higher amendment rates of 6, 8 and 10%, six botanicals suppressed the disease. Dry powders are not only superior in disease suppression but confer additional benefits like reduced bulk, increased shelf life, consistent composition and results.

Induction of Resistance against Sorghum Downy Mildew by Seed Treatment with Duranta repens Extracts

Induction of resistance against plant diseases by seed treatment is simple, cost effective and an efficient strategy for disease management. Aqueous extracts of three plants namely, Duranta repens, Polyalthia longifolia and Parthenium hysterophorus were evaluated for induction of resistance against sorghum downy mildew at 2.5% and 5% concentrations by seed dip method. Seeds were dipped for 3 h, followed by decanting and incubation to obtain sprouts. The sprouts obtained after 42 h incubation were inoculated by dipping in conidial suspension, planted in pots and raised in greenhouse conditions to observe systemic disease incidence. Duranta repens extract at 2.5% and 5% concentrations provided protection of 50.9% and 85% respectively, as against 38.5% protection provided by positive control. Biochemical analysis showed enhanced levels of defence enzymes PAL and POX in plant extract-treated seedlings. Evaluation of 6 solvent fractions of D. repens revealed disease protection by almost all fractions, indicating synergistic effect by various biochemicals. The method is helpful to attain goal of sustainable agriculture with biological and ecological safety. The novel method developed in the present investigation of using weight of seedlings as indicator of health index is effective and more convenient as compared to measurement of root and shoot lengths.

A novel technique for greenhouse evaluation of plant extracts for management of downy mildew of sorghum

Antipathogenic potential of 16 plants was evaluated in the form of aqueous extracts against Peronosclerospora sorghi, causing downy mildew of sorghum. A novel method was developed in which conidial suspension and plant extracts were mixed individually and allowed to stand for 5 min and then used to inoculate the host by sprout-dip method. The sprouts thus inoculated were grown in pots, and disease incidence was observed. Three extracts (Parthenium hysterophorus, Duranta repens and Oxalis latifolia) suppressed the disease at par with chemical fungicide (Mancozeb 75%). In form of spray, D. repens extract with tween-20 adjuvant (1.9% disease) performed closest behind mancozeb (0% disease), while negative control showed 21% disease incidence. Organic management of airborne inoculum of downy mildew of sorghum is feasible and preferable as compared to the use of chemical fungicides, considering human and environmental health concerns. Use of water extract keeps the technology simple so that it can be directly prepared and used by farmers. Short listing of three most effective water extracts would help in self-reliance of farmers, reducing their dependence on commercial products.

Screening of plant extracts for organic management of downy mildew of sorghum

Antipathogenic potential of 38 plants was evaluated in the form of aqueous extracts against Peronoclerospora sorghi, causing downy mildew of sorghum. Conidial suspension and plant extracts were mixed individually and allowed to stand for 5 min and then used to inoculate the host by sprout-dip method. The sprouts thus inoculated were grown in pots, and the disease incidence was observed. Eight plant extracts (Cicer areatinum, Datura metel, Croton sparsiflorus, Parthenium hysterophorus, Nerium oleander, Chromolaena odorata, Duranta repens and Oxalis latifolia) at 20% concentration performed at par with chemical fungicide (Mancozeb 75%) by exhibiting total suppression of disease incidence to 0%, when compared with 64.1% of negative control. Organic management of air-borne inoculum of downy mildew of sorghum is feasible and preferable when compared with chemical control methods, considering human and environmental health concerns. The use of water extract keeps the technology simple so that it can be directly prepared and used by the farmers. Short-listing of eight most effective water extracts would help in self-reliance of farmers, reducing their dependence on commercial products.

Comparative evaluation of long-term storage techniques on viability and virulence of Alternaria solani

Abstract The study was conducted to test the viability and pathogenicity of different forms of Alternaria solani inoculum stored at different conditions and time intervals for a period of 16 months. The aim was to confirm the survival period of pathogen in soil and to determine the simplest method to maintain inoculum in laboratory for further studies. The cultures stored at 5 °C for 2, 4, 8 and 16 months were pathogenic, while cultures stored at room temperature turned non-pathogenic after 4 months. All 6 successive sub-cultures retained viability and virulence. All the target-spots stored at 5 °C were viable after all time intervals as tested by culturing and subsequent spray of harvested mycelial suspension, but at the room temperature (RT), 16 months old inoculum lost viability and virulence. The powdered tissue samples of target-spots stored at 5 °C were found pathogenic by spray method after all the intervals of the time but, at RT 16 month old sample lost virulence. In inoculation by soil splashing, powdered tissue stored in paper bag at 5 °C retained pathogenicity till 8 months, while at RT, the inoculum stored in paper bags and the inoculum mixed in soil lost pathogenicity after 4 months.

Durantol - a phytosterol antifungal contributor from Duranta repens Linn. For organic Management of Sorghum Downy Mildew

AbstractDowny mildew of sorghum (DMS) has serious implications agronomically worldwide and to-date the search for a potent fungicide is a high priority and necessity. Phytochemicals have proven to be effective against various plant pathogens with minimal or no side effects. Duranta repens aqueous extract exhibited a promising potential as an organic fungicide for management of sorghum downy mildew (Peronosclerospora sorghi) in greenhouse conditions, at low concentration of 5 %. Activity guided bio-prospecting lead to the isolation of active principle which could control the DMS at as low as 0.1 % concentration. Spectral studies identified the bioactive contributor as a phytosterol namely 16-Hydroxy-8,10,13-trimethyl-1,2,8,10,12,13,14,15-octahydro cyclopenta [a] phenanthren-3-one, designated as Durantol. The results of microscopy exhibited the inhibition of conidial germ-tube growth by formation of bulb-like swellings at the tip, suggesting the mechanism of action of Durantol was via hampering the membrane integrity of the pathogen. Further, the same was virtually predicted using molecular docking for structure-activity relationship (SAR) against four best known membrane receptors namely 1-UDP-glycosyltransferases (UGT), cytochromes P450 (P450), oxidosqualene cyclase (OSC) and serine carboxypeptidase-like acyltransferase (SCPL), proposing that glycosylation onto the membrane would be a reason for inhibition and which is evident from atomic contact energy (ACE) values. The results of the study indicate that, organic management of airborne inoculum of downy mildew of sorghum is feasible and preferable, as compared to the use of chemical fungicides, considering human and environmental health concerns. Graphical abstractᅟ

Evaluation of uncomposted botanical-based soil amendments for organic management of downy mildew of Sorghum

Uncomposted dried, powdered biomass of 38 selected botanicals was evaluated as soil amendments in a pot experiment for their potential to suppress downy mildew of sorghum caused by soil-borne oosporic inoculum of Perenosclerospora sorghi. A negative control showed 11.1% disease incidence. Six botanicals proved effective in form of dry biomass powder at 0.5% (w/w) amendment rate to control infection by oospores (Allium cepa 0%, Lantana camara 1.6%, Polyalthia longofolia 0%, Hyptis suaveolens 1.5%, Eucalyptus globulus 0% and Nerium oleander 1.6% of disease incidence). Dry powders are not only effective in disease suppression but confer additional benefits over composts like reduced bulk, increased shelf-life, consistent composition and results.