Screening the antifungal properties of essential oils against Phytophthora colocasiae

Recently Microbicidal and micro-static activities of naturally obtained botanicals have been extensively explored, generally in response to the devastating apprehension of consumers towards the safety of edible products. However, scientists are paying more interest in using bio pesticides and phytochemicals that constitute environmentally favorable, non-toxic, long-lasting, and productive substitutes for preventing many hazardous plant pathogens. This research aimed to investigate the antifungal capabilities of sage and tea tree essential oils towards taro leaf blight, the most important cause of worldwide production losses. Using synthetic fungicides is a rapid and effective approach for controlling plant diseases, but it also creates human health risks, environmental threats, and chances of pathogen resistance. The essential oils of sage and tea tree were obtained by microwave-assisted hydro-distillation, and their chemical components were analyzed using FTIR spectroscopy. The main components of the oil were Thujone and Terpinen-4-ol, in sage and tea, respectively. A casual disease agent isolated from symptomatic taro leaves is used as a test fungus and identified as Phytophthora colocasiae. The antifungal properties of both essential oils were evaluated against mycelium, sporangium, zoospores, leaf necrosis, and corm lesions. Repeated experiments showed that the minimum concentrations for obtaining 100% inhibition of mycelium, zoospore germination, sporangia formation, and leaf necrosis were estimated at 2.5 and 5.0 mg/mL of sage and tea tree oils, respectively. Outcomes of this study provide an allusion for the prevention and curation of plant diseases promptly, economically, and environmentally by using phytochemicals and plant essential oil derivatives.

Ecological and biological features of silver birch (Betula pendula) in the conditions of an industrial city

The article provides data on phenology, on the content of ascorbic acid in Betula pendula Roth., growing in the conditions of the industrial city of Naberezhnye Chelny in the Republic of Tatarstan, which is a region of the Russian Federation. It is noted that natural phytocenoses are characterized by lower air temperatures in comparison with plantations of sanitary protection zones of industrial enterprises and highway plantings. According to phenological data, in urban plantings, there was observed an increase in defects, a decrease in the vital state, which is associated with severe damage to leaf blades, the formation of leaf necrosis, a decrease in the living area of leaves, which is a consequence of an intense technogenic load on woody plants. It was revealed that the content of ascorbic acid in birch leaves depends on the vegetation stage.

Comparison of Salt Exclusion in Muscadine and Interspecific Hybrid Grapes Using a Greenhouse Screening Procedure

Bunch grapes (Euvitis) are classified as moderately salt-tolerant. However, little is known about the salt tolerance of muscadine grapes (Vitis rotundifolia). The objective of this research was to evaluate the salt exclusion capacity of muscadine grapes relative to common bunch grape rootstocks and hybrid winegrapes using a greenhouse screening assay. In two separate experiments, 31 muscadine, six bunch grape rootstocks, and five hybrid winegrape cultivars were irrigated daily with a 25-mm sodium chloride salt solution for a period of 14 d, followed by a destructive harvest to determine sodium (Na) and chloride (Cl) concentrations in root and shoot tissues. Generally, the muscadines studied exhibited a greater range of salt concentration relative to bunch grape rootstocks. Total tissue (shoot and root) salt varied by 250% and 430% across muscadines and by 180% and 190% across bunch grape rootstocks for Na and Cl, respectively. Despite the wider range, muscadine grapes expressed significantly less leaf necrosis than the bunch grape rootstocks. The most effective salt-excluding muscadines, ‘Janebell’, ‘Scuppernong’, ‘Late Fry’, and ‘Eudora’, were not distinguishable from the bunch grape rootstocks [‘Paulsen 1103’ (1103P), ‘Ruggeri 140’ (140Ru), ‘Schwarzmann’, ‘Millardet et de Grasset 101-14’ (101-14 Mgt.), ‘Millardet et de Grasset 420A’ (420A), and ‘Matador’]. Overall, there was no discernable difference between the salt exclusion capacity of muscadine and bunch grapes. The hybrid winegrape ‘Blanc Du Bois’ displayed poor Na and Cl exclusion properties but showed only moderate leaf necrosis symptoms. In both experiments, ‘Blanc Du Bois’ accumulated more than two-fold higher root and shoot concentrations of Na and Cl compared with the best-performing rootstocks (1103P, 140Ru, 101-14 Mgt.), suggesting that ‘Blanc Du Bois’ could benefit from grafting if salinity is a limiting factor.

2-Hydroxymelatonin, Rather Than Melatonin, Is Responsible for RBOH-Dependent Reactive Oxygen Species Production Leading to Premature Senescence in Plants

Unlike animals, plants amply convert melatonin into 2-hydroxymelatonin (2-OHM) and cyclic 3-hydroxymelatonin (3-OHM) through the action of melatonin 2-hydroxylase (M2H) and melatonin 3-hydroxylase (M3H), respectively. Thus, the effects of exogenous melatonin treatment in plants may be caused by melatonin, 2-OHM, or 3-OHM, or some combination of these compounds. Indeed, studies of melatonin’s effects on reactive oxygen species (ROS) production have reported conflicting results. In this study, we demonstrated that 2-OHM treatment induced ROS production, whereas melatonin did not. ROS production from 2-OHM treatment occurred in old arabidopsis leaves in darkness, consistent with an ethylene-mediated senescence mechanism. Transgenic tobacco plants containing overexpressed rice M2H exhibited dwarfism and leaf necrosis of the upper leaves and early senescence of the lower leaves. We also demonstrated that 2-OHM-mediated ROS production is respiratory burst NADPH oxidase (RBOH)-dependent and that 2-OHM-induced senescence genes require ethylene and the abscisic acid (ABA) signaling pathway in arabidopsis. In contrast to melatonin, 2-OHM treatment induced senescence symptoms such as leaf chlorosis and increased ion leakage in arabidopsis. Senescence induction is known to begin with decreased levels of proteins involved in chloroplast maintenance, including Lhcb1 and ClpR1. Together, these results show that 2-OHM acts as a senescence-inducing factor by inducing ROS production in plants.

Rust (Puccinia emaculata) management and impact on biomass yield on switchgrass

Rust, putatively caused by Puccinia emaculata, is a widespread and potentially damaging disease of switchgrass, a crop produced as feedstock for livestock and bioenergy. Azoxystrobin, chlorothalonil, and myclobutanil were applied at 1-, 2-, 3-, or 4-wk intervals for 12 to 14 wks to the vegetatively propagated switchgrass cultivar ‘Cloud Nine’ to assess fungicide selection and application interval for the control of rust as well as the impact of this disease on switchgrass biomass yield. While rust severity significantly differed among study years, azoxystrobin and myclobutanil were often equally and more effective than chlorothalonil at controlling rust, with superior disease control coming at the shorter compared to extended application intervals. Year, product, application interval, and product × interval significantly impacted dry biomass yield, which was greatest in 2016 and lowest in 2014. Dry biomass yield protection was significantly better with azoxystrobin and myclobutanil applications than with chlorothalonil or no fungicide. Linear regression models with the final disease rating, as well as with AUDPC in each year, were significant but coefficients of determination were low to moderate (0.21 < R2 < 0.60), indicating that rust response and subsequent disease impact on dry biomass yield were impacted by other factors. From our models, an estimated 3 to 5% biomass decline was calculated for each 10% increment in rust-related leaf necrosis observed at the final September rating date. With rust-related leaf necrosis > 80% by 1 Sept in each of four study years, biomass yield may be reduced by 24 to 40% if rust problems are not managed in switchgrass crops.

Relationships between pest density and associated leaf necrosis for an invasive leaf-mining weevil, Orchestes fagi L., on American beech (Fagus grandifolia Ehrh.)

Pest density-plant damage relationships are essential guides for decision-making in Integrated Pest Management. In this article, we established pest density-leaf damage relationships for the beech leaf-mining weevil,<i></i> Orchestes fagi <i></i>(L.) (formerly <i></i>Rhynchaenus fagi<i></i>, Coleoptera: Curculionidae) in its invasive range of Nova Scotia, Canada. Outbreaks of<i> O. fagi</i> cause tree-wide leaf necrosis in American beech (<i>Fagus grandifolia</i> Ehrh.), which can eventually result in tree mortality. In 2014 and 2016, we collected weekly samples in stands with American beech and assessed leaves for densities during different life stages (eggs, larvae, and pupae), population proxy measures (adult feeding damage, egg slits, and larval galleries), and percent necrosis. In general, feeding damage and leaf necrosis plateaued soon after end of budburst, but before larval mine expanded. This strongly suggested that leaf necrosis may be linked to damage caused by adults or mine initiation rather than that caused by larval mine expansion and gallery development. Density of <i>O. fagi</i> per leaf for life stages and population proxies all significantly explained ~ 42–81% of the variation in end-of season percent leaf necrosis. Results from this study provide a variety of relationships that could be used in both short- and long-term monitoring efforts for <i>O. fagi</i>.

Antifungal potential of cinnamon essential oils against Phytophthora colocasiae causing taro leaf blight

Background Taro leaf blight, caused by a severely destructive oomycete fungus Phytophthora colocasiae, is responsible for threatening yield loss worldwide. The pathogen has the ability to germinate and spread rapidly to other plants during favorable conditions resulting in acute decline and even death, causing 100% crop loss. Farmers usually rely on highly toxic systemic fungicides to control the disease, which is effective, but residual effects and resistance of these agrochemicals is still a concern. Recently as returning to nature people tend to use chemical-free products, especially edible stuff produced in organic agriculture. Therefore, the use of bio-pesticides and phytochemicals is gaining special attention by scientists as they are ecofriendly non-hazardous, sustainable, and potent alternatives to control many virulent plant pathogens The present research was conducted to assess the antifungal potential of cinnamon essential oils against P. colocasiae. Materials and methods The essential oils from cinnamon bark were extracted using microwave-assisted hydrodistillation equipment, and then their chemical constituents were evaluated using ATR FTIR spectroscopy. The antifungal potential of essential oil was assessed against mycelium, sporangia, zoospore, leaf necrosis, and corms lesions under laboratory conditions at, 0.156, 0.312, 0.625, 1.25, 2.5, 5.0 mg/mL concentrations. Hymexazol was used as positive control and no essential oil as negative control, while each treatment have three replications and experiment repeated twice. Results The main component of oil was identified as cinnamaldehyde. The pathogen isolated from infected taro leaves was identified as P.colocasiae and then was used as a test fungus in the current study. Repeated experiments show maximum inhibition percentage of mycelial growth, zoospore germination, and sporulation of the fungus were observed at 0.625 mg/mL, whereas leaf necrosis was 100% inhibited at 1.25 mg/mL concentration. Conclusion This research can be a reference for easy, cost-effective and environment-friendly management and control of taro leaf blight with phytochemicals and plant essential oil derivatives. Graphic abstract

Attraction of Trichogramma Wasps to Butterfly Oviposition-Induced Plant Volatiles Depends on Brassica Species, Wasp Strain and Leaf Necrosis

Within the Brassicaceae, wild as well as crop species are challenged by specialist herbivores including cabbage white butterflies (Pieris spp.). The wild crucifer Brassica nigra responds to oviposition by Pieris butterflies by the synergistic expression of two egg-killing traits. Genotypes that express a hypersensitive response (HR)-like necrosis (direct egg-killing) also emit oviposition-induced plant volatiles (OIPVs) attracting Trichogramma egg parasitoids (indirect egg-killing). This so-called double defense line can result in high butterfly egg mortalities. It remains unknown whether this strategy is unique to B. nigra or more common in Brassica species. To test this, we examined the response of different Trichogramma evanescens lines to OIPVs emitted by B. nigra and three close relatives (Brassica napus, Brassica rapa, and Brassica oleracea). Furthermore, we evaluated whether HR-like necrosis played a role in the attraction toward plant volatiles. Our results show a specificity in wasp attraction to different plant species. Three out of four plant species attracted a specific T. evanescens strain, including the crops B. rapa and B. napus. Parasitoid attraction was positively affected by presence of HR-like necrosis in one plant species. Our findings imply that, despite being a true generalist in terms of host range, T. evanescens shows intraspecific variation during host searching, which should be taken into account when selecting parasitoid lines for biocontrol of certain crops. Finally, we conclude that also crop plants within the Brassicaceae family possess egg-killing traits and can exert the double-defense line which may enable effective selection of egg-killing defense traits by cabbage breeders.

Bacterial canker of tomato: revisiting a global and economically damaging seedborne pathogen

The Gram-positive actinobacterium Clavibacter michiganensis is the causal agent of bacterial canker of tomato, an economically impactful disease with a worldwide distribution. This seedborne pathogen systemically colonizes tomato xylem leading to unilateral leaflet wilt, marginal leaf necrosis, stem and petiole cankers, and plant death. Additionally, splash dispersal of the bacterium onto fruit exteriors causes bird’s-eye lesions, which are characterized as necrotic centers surrounded by white halos. The pathogen can colonize developing seeds systemically through xylem and through penetration of fruit tissues from the exterior. There are currently no commercially available resistant cultivars, and bactericidal sprays have limited efficacy for managing the disease once the pathogen is in the vascular system. In this review we summarize research on epidemiology, host colonization, the bacterial genetics underlying virulence, and management of bacterial canker. Finally, we highlight important areas of research into this pathosystem that have the potential to generate new strategies for prevention and mitigation of bacterial canker.