Antifungal effect of essential oil and different extracts obtained from Nepeta meyeri on Botrytis cinerea

The study concerns the antifungal effect of the aqueous and methanolic extracts, and the essential oil obtained from the aerial parts of Nepeta meyeri Benth. on Botrytis cinerea Pers. The fungus has been isolated from the infected plants of common grape Karaerik (Vitis vinifera L.) cultivating in vineyards in Üzümlü district, Erzincan (Turkey), and was cultured on potato dextrose agar medium in Petri dishes after the identification by 18S rRNA gene-based PCR assay. The concentrations of extracts from N. meyeri in Petri dishes were 2%, 5% and 10% (w/v) for aqueous extract (AE); 500, 1000 and 1500 ppm (v/v) for methanolic extract (ME), and 0.6, 0.8 and 1 µL for essential oil (EO). After the treatments, mycelial growth, spore germination, and germ tube elongation were determined. Sterile distilled water at the same ratios was used for the control treatment. Thirty-six different compounds were identified in the EO of N. meyeri by GC/MS. The highest antifungal activity has been registered for EO of N. meyeri. The inhibition rates in 1 µL/Petri of the EO were 80.72%, 18%, 38.15% on mycelial growth, spore germination and germ tube elongation, respectively. However, AE and ME of N. meyeri showed diverse effects on the studied parameters of B. cinerea. It is suggested that the favourable concentration of EO from N. meyeri can contribute to the prevention of B. cinerea infection (grey mould) which causes disease in vineyards.

Growth-inhibiting activity of citronella essential oil to multiple fungal plant pathogens

Cymbopogon species are among the most reported essential oils with fungitoxic effect. In this study, mycelial growth of Fusarium oxysporum (banana wilt), Colletotrichum gloeosporioides (mango anthracnose), C. falcatum (sugarcane red rot) and Neopestalotiopsis spp. (mango leaf spot) as influenced by varying concentrations of citronella essential oil (CEO) was assessed in in vitro assays. Following growth inhibition test, spore germination and germ tube elongation of C. gloeosporioides were then examined. Mycelial growth of all test fungal pathogens was strongly inhibited by CEO, but variations were observed among fungal species. This growth inhibition activity was caused by the inhibition of spore germination and germ tube elongation as observed in C. gloeosporioides. The findings of this study show the strong growth-inhibitory activity of CEO to multiple fungal pathogens, indicating CEO’s potential as a chemical control approach against these fungal pathogens. Glasshouse and field experiments would establish CEO as one potential alternative to fungicides.

In Vitro Effects of Five Different Classes of Fungicides on Growth and Development of Botrytis cinerea Isolated from Tree Peony in China

Gray mold caused by Botrytis cinerea has become an important limiting factor for tree peony production. Currently, chemical control is still the main means of managing the disease in China. The objective of this study was to test fungicides with different mechanisms of action in controlling B. cinerea on tree peony. The inhibitory efficacy of five fungicides on four asexual stages was measured in the petri dish containing culture medium amended with a tested fungicide at various concentrations. The results showed that carbendazim had the strongest inhibition effect against all four stages of B. cinerea, with the EC50 values of 0.1037, 0.0563, 0.5578, and 0.0797 mg·L–1, respectively. The inhibitory effect of diethofencarb was only slightly less than that of carbendazim on conidia production, germination, and germ tube elongation. The inhibitory effect of procymidone was second only to that of carbendazim on colony expansion. The results indicated that carbendazim and diethofencarb could be used as protective fungicides to spray in the early stage of disease occurrence to inhibit conidia germination and germ tube elongation, so as to reduce the infection rate of B. cinerea and prevent disease occurrence. Carbendazim, procymidone, and diethofencarb mainly inhibit the reinfection of B. cinerea by inhibiting the growth of mycelium and the production of conidia, so they could be used as control fungicides during the occurrence phase of the disease.

Effect of Legume Extracts on Germination, Seedling Health of Beans (Phaseolus vulgaris L.) and Soil Microorganisms

Application of undecomposed green manure has been reported to cause poor emergence and establishment of common beans in the field. Therefore, to understand the mechanisms’ contributing to the poor crop establishment, the effect of extracts from fresh and decomposed legume green manures on bean seed germination, fungal mycelial growth, spore germination and germ tube elongation were evaluated. The extracts were prepared in either ethanol or distilled water. Data was collected on percentage seed germination, seedling length, mycelial radial growth, spore germination and germ tube elongation. Ethanol extracts from fresh lablab inhibited bean germination by 56%, increased mean germination time to 8 days, and decreased germination index while ethanol extracts of groundnut and beans caused highest inhibition in bean shoot length and reduced biomass. Ethanol extracts from fresh green manures significantly inhibited fungal mycelial growth while the aqueous extracts from beans, groundnuts and soybean had significant level of antifungal activity while aqueous lablab extracts stimulated mycelial. Aqueous extract of lablab and soybean enhanced spore germination by over 70% with more pronounced effect on germ tube length and number of germ tubes by 8.0% and 13% respectively. The study comparatively reveals that the extract of lablab was inhibitory to common bean germination compared to other legume extracts and also stimulated the growth of root rot pathogens that may have resulted in poor establishment of beans.

Antifungal Efficacy of Plant Oils Containing Thymol and Carvacrol in Controlling Botrytis cinerea, the Causal Agent of Grape (Vitis vinifera) GrayMould

The efficacy of a large number of plant extracts and essential oils in controlling plant diseases has been proven worldwide. Botrytis cinerea has attacked a wide host range causing severe loss in the field and at storage. In this study the antifungal efficacy of essential oils of three medicinal plants namely wild marjoram (Zataria multifolia), wild savory (perennial) (Satureja mutica) and savory (annual) (Satureja hortensis) possessing these compounds at three concentrations: 50, 100 and 200 ppm were evaluated in controlling the mycelial growth, spore germination and germ tube elongation of B. cinerea. All treatments except savory (annual) essential oil at 50 ppm showed significant differences with the control in inhibiting the mycelial growth as well as spore germination and germ tube elongation of B. cinerea (p=0.01). It was also noted that wild marjoram at 100 ppm and wild savory (perennial) essential oils at 200 ppm could completely (100%) inhibit the growth of the fungus. Essential oils from wild marjoram and wild savory had higher antifungal activity than annual savory. Their suitable formulations could be prepared and used as safe alternatives for controlling moulds of horticultural products during storage. The Agriculturists 2018; 16(2) 15-24

Bacillus cereusHS24 Suppresses Conidia Germination ofMagnaporthe oryzaeby Inhibiting the Ca2+Signaling Pathway

Rice yield is greatly reduced due to rice blast, a worldwide multi-cycle fungal disease caused by the ascomyceteMagnaporthe oryzae.Previously,Bacillus cereusHS24 was isolated from rice growing area, which showed a strong bio-control effect onM. oryzae.In order to better exploit it as a bio-control agent, HS24 has been studied for its mechanism of controlling rice blast. Our results showed that conidial germination ofM. oryzaewas significantly inhibited by HS24 suspension,nand the inhibition rate reached to 97.83% at the concentration of 10 CFU/ml. The transcriptional level ofCAMKII, PMC1andCCH1,which are key genes involved in Ca2+signaling pathway, were significantly decreased in HS24-treated conidia. The treatment ofM. oryzaewith Ca2+signaling pathway inhibitors KN-93, Verapamil, and cyclopiazonic acid (CPA) significantly reduced conidial germination rate and inhibited germ tube elongation. This inhibition effect was found to be concentration-dependent, similar to the HS24 treatment. By quantifying free Ca2+inM. oryzaeconidia, a significant reduction of intracellular free Ca2+concentration in HS24-treated conidia in comparison to sterile water-treated conidia was found. The addition of exogenous Ca2+did not abolish the inhibitory effect of HS24 on the reduction of intracellular free Ca2+concentration and conidial germination. In conclusion,B. cereusHS24 can inhibit conidial germination by suppressing Ca2+signaling inM. oryzae,and thus offers a great potential as a bio-control agent in rice blast management.ImportanceIn the bio-control of rice blast, most of researches focused on the inhibitory effect of bio-control agents on development ofM. oryzae, including inhibition of conidia germination, germ tube deformity, mycelium growth inhibition, etc, while little work has elucidated the molecular mechanisms underlying the various phenotypic change inM. oryzae.In order to better exploit HS24 as a potential bio-control agent, we studied the molecular mechanisms underlying the suppression ofB. cereusHS24 onM. oryzaeGuy11, and draw the conclusion that HS24 may inhibit conidia germination and germ tube elongation through inhibiting the Ca2+signaling pathway. In this study, we characterized the morphological and physiological changes ofM. oryzaewhen interacting withB. cereusHS24, and further investgated the responses ofM. oryzaeCa2+signallig pathway to HS24 treatment. Thus we have provided one more piece for theB. cereus/M. oryzaesupression puzzle at the molecular level.

Resistance in Strawberry Isolates of Colletotrichum acutatum from Florida to Quinone-Outside Inhibitor Fungicides

Anthracnose fruit rot of strawberry, caused by Colletotrichum acutatum, is a major disease in Florida and frequent quinone-outside inhibitor (QoI) fungicide applications are needed for disease control. From 1994 to 2014, 181 C. acutatum isolates were collected from multiple strawberry fields in Florida with or without QoI spray history. Sensitivity to azoxystrobin and pyraclostrobin was tested based upon mycelial growth and germ tube elongation inhibition. Mean effective concentration where growth was reduced by 50% (EC50) values for isolates collected prior to 2013 based upon mycelial growth were 0.22 and 0.013 μg/ml and upon germ tube elongation were 0.57 and 0.03 μg/ml for azoxystrobin and pyraclostrobin, respectively. Mycelial growth and germ tube elongation of 48 isolates collected in 2013 and 2014 were not inhibited with azoxystrobin at 3 μg/ml and pyraclostrobin at 0.110 μg/ml. A fungicide discriminatory dose assay indicated that 43 of the 48 isolates had EC50 values higher than 100 and 10 μg/ml for azoxystrobin and pyraclostrobin, respectively. Azoxystrobin and pyraclostrobin sprayed preventively on strawberry fruit inoculated with C. acutatum failed to control resistant isolates. Sequencing of the cytochrome b gene of sensitive and resistant isolates showed that QoI-resistant isolates contained either G143A or F129L amino acid substitutions.