Antifungal activity of ethanolic extract of Archu (Rheum emodi) on powdery mildew (Erysiphe cichoracearum) and its role in the induction of resistance in balsam (Impatiens balsamania)

Rheum emodi, vernacularly known as Archu, is one of the important high altitude medicinal plants widely distributed in Himalayan regions. Though widely used in Ayurveda for curing various human diseases, its use in plant diseases is limited. Ethanolic extract of Rheum rhizome was assayed against spore germination of Alternaria solani, Heliminthosporium penniseti and Curvularia palliscens. The inhibition of spore germination was concentration dependent. Maximum inhibition was obtained at 4000 and 5000 ppm followed by 3000, 2000 and 1000 ppm. However, the extract was highly effective in the pre-inoculation treatment against powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsamania) under field conditions. High performance liquid chromatographic (HPLC) analysis of balsam leaves showed increased synthesis of phenolic acids, which has been correlated with induced resistance in inhibiting the disease intensity of balsam powdery mildew.     

Antifungal activity of two alkaloids of Zephyranthes citrina and their field efficacy against powdery mildew (Erysiphe cichoracearum) of balsam

The anti-fungal activity of two alkaloids isolated from bulbs of Zephyranthes citrina was observed against 10 fungi, viz, Aternaria solani, A. triticina, Curvularia lunata, C. maculuns, Cercospora malvacearum, Erysiphe sp., Fusarium udum, Helminthosporium pisi, H. speciferum and Ustilago cynodontis. Different concentrations (200, 400, 600, 800, 1000 µg/ml of alkaloids (A and B) were used. Spore germination was inhibited at 600, 800, 1000 µg/ml. B alkaloid was used against Erysiphe cichoracearum causing powdery mildew in balsam (Impatiens balsamina) in the field as pre- and post-inoculation treatments at 1000, 1500, 2000 µg/ml doses. The extract was effective in both pre- and post-inoculation treatments. Foliar application of this alkaloid resulted in inducing synthesis of phenolic acid in the leaves of balsam. Maximum phenolics were detected in the leaves treated with 1500 µg/ml in both pre- and post-inoculation treatments. The increase in the production of phenolics in treated leaves of balsam can be correlated with the induction of resistance in treated plants against powdery mildew. The significant efficacy of the alkaloid under field conditions opens the possibility of its use by farmers for also controlling other diseases.     

Antimicrobial efficacy,disease inhibition and phenolic acid-inducing potential of chloroform fraction of cow urine

High-performance liquid chromatographic (HPLC) analysis of chloroform fraction (CF) of cow urine showed rich pool of phenolic acids. Antifungal and antibacterial bioassays of CF have shown its tremendous efficacy against some fungal plant pathogens as well as human pathogenic bacteria at very low concentrations. The CF also inhibited powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsamania) under field conditions during pre- and post-inoculation treatments. HPLC analysis of pre- and post-inoculation-treated plant leaves indicated that CF induced phenolic acid synthesis as compared to control. The results revealed that CF of cow urine has the potential for controlling some important human diseases. The result on balsam powdery mildew is a good signal that CF may also be effective against other plant diseases in the field.     

Effects of neem seed derivatives on behavioral and physiological responses of the Cosmopolites sordidus (Coleoptera: Curculionidae)

Both in a choice and multi-choice laboratory tests, fewer adults of the banana root borer, Cosmopolites sordidus (Germar), settled under the corms of the susceptible banana "Nakyetengu" treated with 5% aqueous extract of neem seed powder or cake or 2.5 and 5% emulsified neem oil than on water-treated corms. Feeding damage by larvae on banana pseudostem discs treated with 5% extract of powdered neem seed, kernel, or cake, or 5% emulsified neem oil was significantly less than on untreated discs. The larvae took much longer to locate feeding sites, initiate feeding and bore into pseudostem discs treated with extract of powdered neem seed or kernel. Few larvae survived when confined for 14 d on neem-treated banana pseudostems; the survivors weighed two to four times less than the larvae developing on untreated pseudostems. Females deposited up to 75% fewer eggs on neem-treated corms. In addition, egg hatching was reduced on neem-treated corms. The higher the concentration of neem materials the more severe the effect.     

Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) as a potential mycoparasite on Sphaerotheca fuliginea (Ascomycotina: Erysiphales)

Hyphomycete Paecilomyces fumosoroseus that is well known as saprophytic and entomopatogenic fungus was investigated for its mycoparasitism on the cucumber powdery mildew pathogen. Mycoparasitism was documented by using standard bioassay and SEM. Effects of mycoparasitism were evaluated in three types of experiments. Paecilomyces fumosoroseus was applied in the form of graded suspensions into a colony of powdery mildew on a leaf segment. Interaction between both fungi was observed as the percentage of colonized area vs. experimental time. In the second experiment, young cucumber plants were sprayed with a suspension of Paecilomyces fumosoroseus 24 h before inoculation of Sphaerotheca fuliginea. Pre-treatment with P. fumosoroseus reduced development and spreading of powdery mildew infection significantly 15 days post-inoculation in contrast to pre-treatments with sulfur fungicide and distilled water. The development of pure culture powdery mildew under determined experimental conditions was observed and compared with treated variants. In the third experiment, mildewed plants were treated with a suspension of P. fumosoroseus. The control treatments with sulfur fungicide and distilled water were tested. Effects of P. fumosoroseus on the dispersion of powdery mildew during a 21-day period were observed.P. fumosoroseus suppressed the development and spread of cucumber powdery mildew significantly during the time of the experiment. The mechanical and physical damages and disruptions of vegetative and fruiting structures of powdery mildew were recorded under light microscopy and S.E.M.Results were concluded in pursuance to differences between the natural behaviour and development of S. fuliginea on cucumber plants treated with P. fumosoroseus and non-treated plants.     

Use of plant extracts and biocontrol agents for the management of brown spot disease in rice

Fifty plant extracts, four oil cakes and eight antagonistic organisms were tested against Bipolaris oryzae (Cochliobolus miyabeanus), the causal agent of brown spot disease of rice. In vitro studies indicated that two leaf extracts, Nerium oleander and Pithecolobium dulce exerted the higher percent inhibition to mycelial growth (77.4, 75.1%) and spore germination (80.3, 80.0%) of B. oryzae. Among the four oil cake extracts tested in vitro against B. oryzae, neem cake extract showed the maximum inhibition percent to mycelial growth (80.18%) and spore germination (81.13%) of the pathogen followed by mahua cake extract, castor and gingelly cake extract. Trichoderma viride (Tv2) was significantly effective in inhibiting the mycelial growth (62.92%) and spore germination (77.03%) of the pathogen followed by Trichoderma harzianum (Th5) and Trichoderma reesei (Tr3). The promising leaf extracts, oil cake extracts and antagonistic microorganisms were further evaluated for their efficacies in disease management under glasshouse and field conditions. In glasshouse studies, post-infectional spraying of rice plants with neem cake extract, N. oleander leaf extract and T. viride (Tv2) was significantly effective in reducing the incidence of brown spot of rice by 66, 52 and 45 percent respectively. Two rounds of spraying of rice plants with neem cake extract, N. oleander leaf extract and T. viride (Tv2) in the field at initial appearance of disease and 15 days later reduced the incidence of brown spot (70, 53 and 48% disease reduction respectively) and increased the yield by 23, 18 and 15 percent respectively.     

Induction of defence-related biochemical changes in okra leaves to powdery mildew disease by several plant-derived agents

Certain plant-derived agents (PDA) which could induce resistance in okra leaves against powdery mildew (Erysiphe cichoracearum) and biochemical changes in treated leaves were investigated during 2011 and 2012 growing seasons. At the two-leaf old, four- and eight-week leaves of the greenhouse-grown okra plants were sprayed with either PDA two days before inoculation with conidia. Among all tested PDA, neem seed oil (NSO) caused the highest protection, followed by jojoba oil (JO) and extract of Reynoutria sachalinensis. Moreover, levels of total protein, activity of peroxidase, polyphenyloxidase and chitinase and total phenols content of treated two-leaf old highly increased after application of NSO and JO, but not by the pathogen (untreated control). Finally, based on conidia germination, lack of the fungitoxic effect of JO and RE and also the slight effect of NSO (9–13.75%) may demonstrate the main role of these agents for inducing resistance through the activation of biochemical defence in treated leaves.     

Biochemical Investigations of Sclerotial Exudates of Sclerotium rolfsii and their Antifungal Activity

Exudates from sclerotia of two Sclerotium rolfsii isolates (one causing collar rot in Cicer arietinum, isolate VC971, and the other leaf spots in Rauvolfia serpentina, isolate VL016) were assayed for their antifungal activity against 26 fungi consisting of plant parasites as well as saprophytes. Spore germination of all the test fungi was affected by the exudates reaching 100% in some cases. Foliar spray with exudates of isolate VL016 significantly reduced disease incidence of balsam (Impatiens balsamina) powdery mildew caused by Erysiphe cichoracearum and pea (Pisum sativum) powdery mildew caused by Erysiphe pisi, under field conditions. Characterization of exudates from 25 isolates of S. rolfsii revealed pH ranging from 3.8 to 5.3 and colour from light yellow to deep yellow. Among the phenolic acids found in the exudates were tannic, gallic, caffeic, vanillic, ferulic, chlorogenic and cinnamic acids. Oxalic acid was also found in varied amounts. Among the phenolic acids, ferulic acid was found to be present at high concentration in exudates of most isolates (3.9–153.4 μg/ml). The antioxidant properties of phenolics, which generally inhibit fungal morphogenesis including spore germination along with the antifungal nature of some phenolics are chiefly attributed to the inhibitory effect of sclerotial exudates of S. rolfsii. Additionally, both the isolates VC971 and VL016 showed almost similar antifungal activities despite they are of different origin and thereby demonstrate the antifungal nature of sclerotial exudates.     

Management of powdery mildew and gray mold of cucumber by Trichoderma harzianum T39 and Ampelomyces quisqualis AQ10

Two biocontrol preparations were tested for their ability to control Sphaerotheca fusca and Botrytis cinerea on greenhouse cucumber. Trichoderma harzianum T39 (TRICHODEX) spray reduced powdery mildew severity by up to 97% but its efficacy declined to 18–55% control as the epidemic progressed. Unlike on young leaves, on older leaves the control of powdery mildew by T. harzianum T39 was poor. Ampelomyces quisqualis (AQ10) was very effective against powdery mildew, achieving up to 98% of control. Its effectiveness declined with the progress of the epidemic but unlike the other biocontrol agent it retained significant control capability on older leaves. Two aliphatic petroleum distillate oil products improved the efficacy of both biocontrol agents. The co-application of T. harzianum T39 and A. quisqualis AQ10 was tested on cucumber plants infected with powdery mildew followed by fruit gray mold infection. It resulted in no improvement of the control of powdery mildew, and in an improvement of gray mold control, the latter probably because of the use of additive oil (ADDQ) along with the second biocontrol preparation. There was no significant interference between the biocontrol agents in the co-application treatment as compared with the application of each agent alone; the level of population of T. harzianum T39 remained similar and the parasitism of S. fusca by A. quisqualis was not nullified. The application of T. harzianum T39 to soil instead of spraying it resulted in 75–90% lower powdery mildew coverage on the leaves. It was concluded that the mode of action of T. harzianum T39 in powdery mildew control is induced resistance, not mycoparasitism or antibiotic action.     

Mango powdery mildew Oidium mangiferae an alternative food for the predatory mites Typhlodromus mangiferus and Typhlodromips swirskii (Phytoseiidae) in absence or presence increasing prey density of Oligonichus mangiferus (Tetranychidae) in Egypt

The predacious mites, Typhlodromus mangiferus Zaher and El-Borolossy and Typhlodromips swirskii (Athias-Henriot), reproduced successfully on mango powdery mildew Oidium mangiferae Berthet in absence or presence of spider mite prey Oligonichus mangiferus (Rahman and Sapra) under laboratory conditions of 25 ± 1°C and 60–65% R.H. Adult female of both predators consumed protonymphs of O. mangiferus at different experimental densities. The consumption rate increased with increasing prey densities up to 25 protonymphs/female/day and decreased significantly at 35 and 50 protonymphs/female/day for the two predatory mites. Addition of powdery mildew conidia to each prey density significantly reduced consumption of spider mites at 35 and 50 protonymphs/female/day. Mean eggs/female/day by T. swirskii and T. mangiferus was 0.30 and 0.72 when reared on powdery mildew conidia compared with 1.64 and 1.57 when fed on powdery mildew and tetranychid prey, respectively. This increase in reproduction would have compensated the reduction in protonymph prey consumption due to the presence of mildew conidia. Mite–mildew interactions are discussed.     

Enhanced Nematicidal Activity of Organic and Inorganic Ammonia-Releasing Amendments by Azadirachta indica Extracts

The nematicidal activities of ammonium sulfate, chicken litter and chitin, alone or in combination with neem (Azadirachta indica) extracts were tested against Meloidogyne javanica. Soil application of these amendments or the neem extracts alone did not reduce the root galling index of tomato plants or did so only slightly, but application of the amendments in combination with the neem extracts reduced root galling significantly. Soil analysis indicated that the neem extract inhibited the nitrification of the ammonium released from the amendments and extended the persistence of the ammonium concentrations in the soil. In microplot experiments, tomato plants were grown in pots filled with soils from the treated microplots. The galling indices of tomato plants grown in soil treated with ammonium sulfate or chicken litter in combination with the neem extract or a chemical nitrification inhibitor were far lower than those of plants grown in the control soil or in soil treated with chicken litter, neem extract or nitrification inhibitor alone. However, plants grown in the microplots showed only slight reductions in galling, probably because the soil amendments were inadequately mixed compared to their application in the pot experiments. The extended exposure of nematodes to ammonia as a result of nitrification inhibition by the neem extracts appeared to be the cause of the enhanced nematicidal activity of the ammonia-releasing amendments.     

Evaluation of neem (Azadirachta indica L.) products for the control of root-knot nematode of chilli pepper (Capsicum annum L.)

Chilli pepper is an important vegetable in the diet of Ghanaians but there are some constraints militating against increased production notable among which is nematode infestation. A study was therefore carried out at the plant house of the Faculty of Agriculture, University for Development Studies, Nyankpala to investigate the efficacy of neem products against root-knot nematode of chilli pepper (Capsicum annum L.). The treatments which included 20 g neem leaf powder, 20 g neem cake, 20 g neem seed powder and control were arranged in a completely randomised design with four replications. Neem products significantly reduced (p < 0.05) nematode population, with 20 g of neem leaf powder recording the highest reduction. Similarly, plants treated with neem leaf powder produced a significantly lower (p < 0.05) number of root galls compared to the other treatments. Neem leaf powder could be used as a nematicide for nematodes control as a replacement for synthetic nematicides.     

Endogenous Abscisic Acid in Wheat Plants upon Inoculation with the Powdery Mildew Causative Agent (Erysiphe graminisf. sp. tritici)

We studied the dynamics of the abscisic acid content in above-ground parts of wheat cultivars with different resistance against powdery mildew. It was assayed by the HPLC method in healthy and diseased (inoculated by the powdery mildew causative agent) plants (from inoculation to the stage of pathogen spore formation). The results are discussed with special reference to the wheat resistance against the powdery mildew.     

Effects of elevated atmospheric CO2 and temperature on the management of powdery mildew of zucchini

The impact of combined environmental factors, such as temperature and CO₂, on the control of the powdery mildew of zucchini, caused by Podosphaera xanthii, and of different control measures has been studied on plants grown in phytotrons. Five experimental trials were conducted, and the powdery mildew severity of both treated and untreated zucchini plants was found to be significantly affected by the interaction between temperature (three different regimes: 16–18; 18–22; 22–26°C), CO₂ (two concentrations: 400–450 and 800–850 ppm) and the treatments. However, at the end of the trials, the efficacy of all the products was not affected by the different, tested environmental conditions. Sulphur consistently provided the highest disease control (75%–85% efficacy). Among the resistant inducers that were tested, calcium oxide was the most effective, in terms of powdery mildew control under all the conditions tested in phytotrons, reducing disease severity from 46% to 61%. Foliar applications of phosphite (14%–28% efficacy), Ampelomyces quisqualis (12%–23% efficacy) and potassium silicate (13%–24% efficacy) only slightly reduced the disease severity for all the tested temperature regimes and CO₂ concentrations, compared to the untreated control. The results obtained under our experimental conditions show that a possible increase in CO₂ concentration and temperature, which is expected for the next few years, should not influence the efficacy of the tested resistance inducers or of sulphur against powdery mildew on zucchini. Moreover, the suppressive effect of calcium oxide is in light of its possible use in greenhouses for zucchini powdery mildew control under 400–450 ppm of CO₂ and under enriched condition of 800–850 ppm of CO₂.     

Glycyrrhiza glabra extract protects plants against important phytopathogenic fungi

In previous investigations an ethanolic plant extract from Glycyrrhiza glabra (2.5% w/v) showed 100% efficacy against late blight (Phytophthora infestans) on detached tomato leaves. Based on these findings, the objective of this work was to investigate the effect of this extract against different important plant pathogenic fungi. Tests were carried out on potted plants. Against P. infestans, efficacies of 75% and 58% were achieved on tomato and potato plants with 5% extract concentration, respectively. Against another Oomycete, Pseudoperonospora cubensis, on cucumber, application of a 2.5% extract led to an efficacy of above 90%. The EC50-value was calculated to be 0.5% In a trial on beans against bean rust (Uromyces appendiculatus), G. glabra extract (5% concentration) showed 92% efficacy. In contrast, against powdery mildew on cucumber (Podosphaera xanthii), no disease reduction was found. Overall, the results indicate a high potential for the extract of G. glabra to control a number of important plant pathogens.     

Artificial elevation of glutathione contents in salicylic acid‐deficient tobacco (Nicotiana tabacum cv. Xanthi NahG) reduces susceptibility to the powdery mildew pathogen Euoidium longipes

• The effects of elevated glutathione levels on defence responses to powdery mildew (Euoidium longipes) were investigated in a salicylic acid‐deficient tobacco (Nicotiana tabacum cv. Xanthi NahG) and wild‐type cv. Xanthi plants, where salicylic acid (SA) contents are normal.
• Aqueous solutions of reduced glutathione (GSH) and its synthetic precursor R‐2‐oxothiazolidine‐4‐carboxylic acid (OTC) were injected into leaves of tobacco plants 3 h before powdery mildew inoculation.
• SA‐deficient NahG tobacco was hyper‐susceptible to E. longipes, as judged by significantly more severe powdery mildew symptoms and enhanced pathogen accumulation. Strikingly, elevation of GSH levels in SA‐deficient NahG tobacco restored susceptibility to E. longipes to the extent seen in wild‐type plants (i.e. enhanced basal resistance). However, expression of the SA‐mediated pathogenesis‐related gene (NtPR‐1a) did not increase significantly in GSH or OTC‐pretreated and powdery mildew‐inoculated NahG tobacco, suggesting that the induction of this PR gene may not be directly involved in the defence responses induced by GSH.
• Our results demonstrate that artificial elevation of glutathione content can significantly reduce susceptibility to powdery mildew in SA‐deficient tobacco.

     

Evaluation of pomegranate (Punica granatum L. var. Gabsi) peel extract for control of root-knot nematode Meloidogyne javanica on tomato

The present study was carried out to assess the nematicidal potential of Punica granatum L. against the root-knot nematode Meloidogyne javanica responsible for yield losses in tomato. Varied concentrations of methanolic, ethanolic and aqueous extracts from pomegranate peels were investigated for activity against eggs and juveniles of M. javanica in in vitro assays. All extracts used significantly inhibited egg hatch by over than 75%, but viability of second-stage juveniles (J2) was not significantly inhibited by ethanolic extract. Aqueous extract was assessed at the concentration of 10, 25 and 50% against M. javanica on tomato in greenhouse trials; pomegranate peels powder was also tested at the rate of 3, 6 and 9 g as a soil amendment. Both extracts significantly reduced nematode infestations; aqueous extract enhanced plant growth but powder amendment exhibited a phytotoxicity compared to the untreated plants. The reduction in number of galls, egg masses and nematode reproduction rate was recorded.     

Effects of fungal infection and wounding on the expression of chitinases and β-1,3 glucanases in near-isogenic lines of barley

Chitinases (EC 3.2.1.14) and β -1.3 glucanases (EC 3.2.1.39) have been known to play a vital role in the defense of plants against fungal pathogens. The pattern of induction of these two enzymes subsequent to infection by powdery mildew was studied in 10 pairs of near-isogenic lines of barley ( Hordeum vulgare L.) which possess powdery mildew resistance genes. These isogenic lines have been grotiped according to their reaction to the fungus. The induction patterns varied between the resistant and the susceptible cultivars within each group and between different groups. More tsozymcs were induced in susceptible varieties of highly resistant groups and the overall levels and the number of isozymes of chitinases and β -1.3 glucanases were lower in groups with low resistance. The effect of powdery mildew infection and mechanical wounding on the cellular localization of chitinases and β -1.3 glucanases in barley leaves has also been studied. The 31 kDa leaf chitinase, L-CH2, and trace amounts of a 25 kDa chitinase. L-CH3. were present in healthy leaves. Wounding increased the levels of L-CH3 within I ft h. Powdery mildew infection increased the levels of L-CH3 both in intercellular fluid and in intracellular extract of leaves. A /3-I.3 glucanase. GH, also increased after infection and wounding. In infected barley leaves, GL-1 was present both in intercellular space and intracellular extract. It is concluded that powdery mildew resistance genes exhibit qualitative and quantitative differences in the expression of chitinases and β -1.3 glucanases. Further, chitinases and β -1.3 glucanases appear to be a response to active infection rather than the factors responsible for disease resistance.     

Use of potassium bicarbonate (Armicarb) on the control of powdery mildew (Sphaerotheca mors-uvae) of gooseberry (Ribes uva-crispa)

Powdery mildew (Sphaerotheca mors-uvae) severely infects young shoots, stems and fruits of gooseberry (Ribes uva-crispa). Environmental friendly and biological control measures are being sought throughout the world. Especially in organic gooseberry growing effective control measures are needed, because powdery mildew infections may result in a total loss of the crop. In organic currant growing the number of adequate control methods is very limited. Sulphur as a fungicide against powdery mildew in e.g. gooseberry or table grape growing is not recommendable due to possible bleaching of berries and scorching of tender shoots. Various bicarbonate salts are suggested as a good option to control powdery mildew. In a field trial the effect of potassium bicarbonate (Armicarb) on the on the control of powdery mildew of gooseberry was evaluated. Four treatments; i.e. two preventive strategies and two curative strategies, were applied. PLants were sprayed until runoff. The percent of infected fruits and disease severity were assessed. In the unsprayed control plots very high disease incidences were observed; on average more than 90% of the berries were infected with powdery mildew. The weekly (preventive) spray applications with potassium carbonate reduced the disease incidences on fruits significantly. On average approximately 10% of the fruits were affected by powdery mildew. However, the number of spray applications was high. In conclusion, our results indicate that applications of potassium bicarbonate (as Armicarb) are effective in reducing the incidence and severity of American powdery mildew in gooseberry. Early spray applications are necessary to protect berries against powdery mildew infections. Future research will focus on reducing the number of applications, e.g. warning models based on powdery mildew of rose (Sphaerotheca pannosa).     

Oleozon: A novel control strategy against powdery mildew in cucumber

Ozonized sunflower oil (oleozon) is an effective agent for controlling powdery mildew in cucumber. In this study, the mechanisms of oleozon in the control of powdery mildew were determined. The development of Podosphaera xanthii on cucumber leaves treated with oleozon (2%) and water was investigated at different times after inoculation. The germinating conidia, hyphae and conidiophores of the pathogen were severely damaged by oleozon. No visible phytotoxic effect was observed on cucumber after the application of oleozon. This compound had highly preventive effects as well as curative effects against powdery mildew based on in vivo potted seedling assays. The control effects of oleozon were further confirmed in a greenhouse trial. These results may provide a basis for further development of a natural fungicide against cucumber powdery mildew.