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Microscopy of sporulation of Peronospora belbahrii on intact basil plants in a dew chamber at 18°C in the dark as a function of time (see Figure 1 for details). Leaf discs were mounted on a glass slide, treated with 0.01% calcofluor and examined with an Olympus-A70 epifluorescent microscope. Bar= 200 µm. doi: 10.1371/journal.pone.0081282.g002
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Peronospora belbahrii is a biotrophic oomycete attacking sweet basil. It propagates asexually by producing spores on dichotomously branched sporophores emerging from leaf stomata. Sporulation occurs when infected plants are incubated for at least 7.5h in the dark in moisture-saturated atmosphere at 10-27°C. Exposure to light suppresses spore format...
Citations
... As regards physical means, Cohen et al. (2017) reported the effectiveness of basil nocturnal illumination, since sporulation in darkness is much higher than under light (Cohen et al. 2013a;López-López et al. 2014). Cohen and Rubin (2015) affirmed that daytime solar heating is an interesting strategy to control BDM, while Cohen and Ben-Naim (2016) stated that nocturnal fanning reduced dew deposition on basil leaves, preventing both infection and sporulation of P. belbahrii. ...
Basil Downy Mildew (BDM), caused by the oomycete Peronospora belbahrii, is a major issue for sweet basil ( Ocimum basilicum L.) production worldwide. Currently, the disease is mainly controlled by chemical fungicides, but the development of populations of the pathogen which are resistant to the most widely used compounds is leading to the research of alternative crop protection strategies. Therefore, in this paper, some cropping variables were tested in a field trial conducted in two consecutive years (2021 and 2022) in Northern Italy in organic farming conditions, with the overall objective to optimize basil productivity and quality and limit BDM occurrence. These include two basil varieties, two sowing densities (dense, 30 kg/ha, and sparse, 15 kg/ha), and two irrigation systems (drip and sprinkler). A higher incidence and severity of BDM in 2022 compared to 2021 was observed, mainly due to the different climatic conditions that occurred in the two years. Year 2022 was characterized by high temperatures and repeated drought phenomena that led to basil stress and BDM severe outbreak. Moreover, variety 1 (considered resistant to P. belbahrii ) was confirmed to be completely resistant in 2021 but it was found to be susceptible the following year, with disease incidence and severity comparable to variety 2 (medium susceptible). No differences were detected in terms of BDM occurrence and crop yield between the two sowing densities (mean of 58.4% and 26.6% of BDM incidence and severity, respectively; mean yield 1.4 kg/m ² ), while it emerged that drip irrigation can be useful in reducing BDM (−23.1% BDM severity). Therefore, this study suggests that the crop protection strategies tested, even if not definitive solutions, can significantly contribute to manage BDM more effectively, while preserving basil productivity and quality.
... Light can both increase plant resistance to phytopathogens [116,[120][121][122][123][124] and decrease it [122,125]. Many studies have shown that microflora is affected not only by white or sunlight per se, but each component of the solar spectrum is important: ultraviolet radiation, blue, far red, etc. Red light has a great influence on the microflora [106,126] and the interaction of plants with microorganisms [114,[123][124][125][126][127][128][129][130][131]. As a rule, red light inhibits the development of phytopathogens and increases plant resistance. ...
... Light can both increase plant resistance to phytopathogens [116,[120][121][122][123][124] and decrease it [122,125]. Many studies have shown that microflora is affected not only by white or sunlight per se, but each component of the solar spectrum is important: ultraviolet radiation, blue, far red, etc. Red light has a great influence on the microflora [106,126] and the interaction of plants with microorganisms [114,[123][124][125][126][127][128][129][130][131]. As a rule, red light inhibits the development of phytopathogens and increases plant resistance. ...
In the present work, we investigated the effect of light conversion using europium (Eu(III))-based photoconversion covers on the cultivation of agricultural plants and their resistance to stress conditions. Two types of europium nanoparticles were used. The first one was obtained from europium oxide (Eu2O3) by laser fragmentation. The second one was Eu3+:LaF3 nanocrystals obtained by hydrothermal-microwave treatment, the content of europium ions in which was 50% of the total amount of cations. Tomatoes (Solanum lycopersicum) and cucumbers (Cucumis sativus) were used as model plants. It was shown that plants grown under cover with Eu2O3 (PCC-Eu2O3) were 30–40% larger, gave a higher yield, and the activation of gas exchange processes and the light phase of photosynthesis in the leaves in response to the lighting was faster. On the contrary, plants grown under cover with Eu3+:LaF3 (PCC-Eu3+:LaF3) tended to slow down the rate of biomass accumulation and decrease the rate of gas exchange activation. It was shown that photoconversion covers change the resistance of plants to stress conditions: if plants grown under PCC-Eu2O3 became more sensitive to heat (+40 °C) and cold (+4 °C) treatment, then plants grown under PCC-Eu3+:LaF3 became more resistant to high and low temperatures. It was found that PCC-Eu2O3 inhibited the development of the phytopathogen Phytophthora infestans on tomato plants. It was assumed that changes in the illumination spectrum by the photoconversion covers cause both the activation of plant growth in the case of Eu2O3 and an increase in plant resistance in the case of Eu3+:LaF3 applications.
... 13 Light as a whole is considered an important environmental factor in fungal growth and development 14 and regulates enzymatic activities. [15][16][17] Photoreceptors in the presence of light activate the light-sensitive genes by signal transduction phenomena. ...
Introduction: There are documents about biological effects of blue light radiation on different organisms. Molecular mechanism understanding of radiation effects on biological samples is an important event which attracted attention of researchers. Determining of the critical dysregulated proteins of Lentinula edodes following blue light radiation is the aim of this study.
Methods: Number of 22 differentially expressed proteins of Lentinula edodes in response to 300 lux of blue light were extracted from literature. Experimental, text mining, and co-expression connections between the queried proteins were assessed via STRING database. The maps were compared and the critical proteins were identified.
Results: Among the 21 queried proteins, six individuals including; heat shock HSP70 protein, 20S proteasome subunit, 26S proteasome subunit P45, Aspartate aminotransferase, Phosphopyruvate hydratase, and Phosphoglucomutase were highlighted as the critical proteins in response to blue light radiation.
Conclusion: Finding indicates that protein homeostasis and glycogen synthesis are affected by blue light radiation.
... causing defoliation and death of sweet basil [6][7]. The disease emerged in Switzerland in 2001 [6], Italy in 2003 [8], France and Belgium in 2004 [9][10], South Africa and Malta in 2005 [11], Iran in 2006, Cameroon 2007 [12] and the United States in 2007 [13-14-15], Argentina in 2008, Cuba and Taiwan in 2009, Hungary and U.K. in 2010 [16][17], Israel and Canada in 2011 [18][19]., and the Czech Republic in 2012 [20], Currently, BDM occurs in all parts of the world where sweet basil is grown. In Egypt basil downy mildew, incited by P. belbahrii Thines, was observed for the first time especially in Beni Suef governorate in 2013 [21] it has become a serious disease in sweet basil and the rapid spread of the pathogen P. belbahrii throughout various herb production regions causing complete crop losses [22]. ...
... Sporangia were harvested with a small paintbrush from the lower surface of basil leaves in a petri dish containing cold sterilized distilled water.1ml of P. belbahrii 1x10 5 sporangia suspension was put in cavity slides on 9 mm plastic plates. Plates were immediately placed into incubation chambers maintained at 10,12,14,16,18,20,22,24,26, and 28°C in darkness. Incubation chamber temperatures were confirmed using analog thermometers. ...
... Temperature is an important environmental factor that influences the germination of sporangia. The sporangia of P. belbahrii were incubated at 10,12,14,16,18,20,22,24, and 28 ºC for 24 hours in sterile distilled water. Data in Table (4) and Fig. (5) shown that the sporangia did not germinate when they were incubated at a temperature of 10 ºC and 28 ºC, while germination started from the degree of 12 ºC (3%), The maximum germination of sporangia were obtained at 18 ºC (33%), moreover, the germination rate of sporangia was not significantly different between 18 and 20 °C, While there was a clear significant difference between these two degrees and the rest of the different temperatures degrees. ...
Basil is the most commercially significant medicinal and aromatic plant, used both fresh and dried, as well as a source of essential oil for perfume and food flavor manufacture. Basil's main composition includes a significant amount of antioxidants and antimicrobial agents. The obligate, biotrophic oomycete pathogen Peronospora belbahrii Thines causes basil downy mildew (BDM). It became a very destructive disease that has caused severe damage and crop loss of sweet basil in Egypt and worldwide. A field survey for disease severity (DS) and disease incidence (DI) of BDM was done in basil cultivation areas in Egypt during two successive growing seasons 2019-2020. The highest percentage of (DS) and (DI) of BDM was (93% and 100%) in 2019 and (95% and 100%) in 2020 in Nassir city of Beni Suef Governorate. Laboratory studies indicated that the highest percentage of spores germination was 33% at temperatures 18 o C and the lowest was 3% at 12 o C, while no spores germinated at 10 o C., the relative humidity percentages 100% and 95% were the most suitable for the highest germination percentage (35% and 33%). The effect of light and dark hours interval (12 hours of light and 12 hours of darkness) was the most suitable for the highest percentage of spores germination (30%). Pathogenicity test by detached leaves method explained that the sporangiophores of P. belbahrii appeared after two days from infection and the severity increased until the 4 th day when the whole leaf was infected. Pathogenicity test under greenhouse condition revealed that P. belbahrii severity and incidence reached (96.6 and 100%, respectively) 7 days post-inoculation in case of sowing basil (Baladi cv.) by seeds while in case of using transplants the disease severity and incidence reached (91.4 and 100%, respectively) at 10 days post-inoculation. The varietal reaction of some basil cultivars to BDM under greenhouse showed that Lemon Basil O. americanum var. citriodorum had the lowest disease severity and incidence (11.0% and 21.6%).
... Furthermore, it can reduce virulence. These effects have been proven for Alternaria alternata (Hubballi et al. 2010), Aspergillus carbonarius (Cheong et al. 2016), Botryodiplodia theobromae (Alam et al. 2001), Botrytis cinerea (Canessa et al. 2013, Zhu et al. 2013Schumacher et al. 2014;Caires et al. 2015), Bremia lactucae (Nordskog et al. 2007), Colletotrichum acutatum (Yu et al. 2013), Cryptonectria parasitica (Hillman et al. 1990), Fusarium graminearum (Beyer et al. 2004), Fusarium verticillioides (Velmurugan et al. 2010), Magnaporthe oryzae (Lee et al. 2006), Peronospora belbahrii (Cohen et al. 2013), Phakopsora pachyrhizi (Li et al. 2010), Plasmopara viticola (Rumbolz et al. 2002) and Puccinia hemerocallidis (Mueller and Buck, 2003;Dong and Buck, 2011). ...
Light is essential for plant life. It provides a source of energy through photosynthesis and regulates plant growth and development and other cellular processes, such as by controlling the endogenous circadian clock. Light intensity, quality, duration and timing are all important determinants of plant responses, especially to biotic stress. Red light can positively influence plant defence mechanisms against different pathogens, but the molecular mechanism behind this phenomenon is not fully understood. Therefore, we reviewed the impact of red light on plant biotic stress responses against viruses, bacteria, fungi and nematodes, with a focus on the physiological effects of red light treatment and hormonal crosstalk under biotic stress in plants. We found evidence suggesting that exposing plants to red light increases levels of salicylic acid (SA) and induces SA signalling mediating the production of reactive oxygen species, with substantial differences between species and plant organs. Such changes in SA levels could be vital for plants to survive infections. Therefore, the application of red light provides a multidimensional aspect to developing innovative and environmentally friendly approaches to plant and crop disease management.
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... Control of BDM has primarily relied on the frequent use of a limited number of fungicides [5], which has led to the evolution of fungicide-resistant strains [7,8]. Deploying fans to reduce humidity during nocturnal periods [9], nocturnal illumination of basil plants [10], or solar heating during daytime [11], has been shown to significantly suppress and reduce the disease, but these measures are associated with increased labor and/or material cost. Considering the scale of commercial farming and the desirability for low-maintenance growing options of home gardeners, the most effective BDM control strategy is to utilize disease-resistant varieties. ...
Sweet basil ( Ocimum basilicum ) is an economically important allotetraploid (2n = 4x = 48) herb whose global production is threatened by downy mildew disease caused by the obligate biotrophic oomycete, Peronospora belbahrii . Generation of disease resistant cultivars by mutagenesis of susceptibility (S) genes via CRISPR/Cas9 is currently one of the most promising strategies to maintain favored traits while improving disease resistance. Previous studies have identified Arabidopsis DMR6 (Downy Mildew Resistance 6) as an S gene required for pathogenesis of the downy mildew-causing oomycete pathogen Hyaloperonospora arabidopsidis . In this study, a sweet basil homolog of DMR6 , designated ObDMR6 , was identified in the popular sweet basil cultivar Genoveser and found to exist with a high copy number in the genome with polymorphisms among the variants. Two CRISPR/Cas9 constructs expressing one or two single guide RNAs (sgRNAs) targeting the conserved regions of ObDMR6 variants were generated and used to transform Genoveser via Agrobacterium -mediated transformation. 56 T0 lines were generated, and mutations of ObDMR6 were detected by analyzing the Sanger sequencing chromatograms of an ObDMR6 fragment using the Interference of CRISPR Edits (ICE) software. Among 54 lines containing mutations in the targeted sites, 13 had an indel percentage greater than 96% suggesting a near-complete knockout (KO) of ObDMR6 . Three representative transgene-free lines with near-complete KO of ObDMR6 determined by ICE were identified in the T1 segregating populations derived from three independent T0 lines. The mutations were further confirmed using amplicon deep sequencing. Disease assays conducted on T2 seedlings of the above T1 lines showed a reduction in production of sporangia by 61–68% compared to the wild-type plants and 69–93% reduction in relative pathogen biomass determined by quantitative PCR (qPCR). This study not only has generated transgene-free sweet basil varieties with improved downy mildew resistance, but also contributed to our understanding of the molecular interactions of sweet basil- P . belbahrii .
... Examples for this complexity are the light effects on Peronosporaceae (oomycetes), wide spread phytopathogens causing downy mildew in diverse agricultural plants. In these oomycetes, RL can inhibit sporulation, e.g., in Peronospora belbahrii, such that exposure to this light quality during night-time effectively inhibits damages to basil plants [26]. However, RL is also Table 1 Summary of photoreceptors types and number of genes encoding for the specified photoreceptors (as X) in plant-associated bacteria for which a role of light has been described; see Table S1 for the specific strains reported to increase the in-vitro germination capacity of Peronospora effusa that causes downy mildew in spinach [27]. ...
Bacteria and fungi of the plant microbiota can be phytopathogens, parasites or symbionts that establish mutually advantageous relationships with plants. They are often rich in photoreceptors for UVA–Visible light, and in many cases, they exhibit light regulation of growth patterns, infectivity or virulence, reproductive traits, and production of pigments and of metabolites. In addition to the light-driven effects, often demonstrated via the generation of photoreceptor gene knock-outs, microbial photoreceptors can exert effects also in the dark. Interestingly, some fungi switch their attitude towards plants in dependence of illumination or dark conditions in as much as they may be symbiotic or pathogenic. This review summarizes the current knowledge about the roles of light and photoreceptors in plant-associated bacteria and fungi aiming at the identification of common traits and general working ideas. Still, reports on light-driven infection of plants are often restricted to the description of macroscopically observable phenomena, whereas detailed information on the molecular level, e.g., protein–protein interaction during signal transduction or induction mechanisms of infectivity/virulence initiation remains sparse. As it becomes apparent from still only few molecular studies, photoreceptors, often from the red- and the blue light sensitive groups interact and mutually modulate their individual effects. The topic is of great relevance, even in economic terms, referring to plant-pathogen or plant-symbionts interactions, considering the increasing usage of artificial illumination in greenhouses, the possible light-regulation of the synthesis of plant-growth stimulating substances or herbicides by certain symbionts, and the biocontrol of pests by selected fungi and bacteria in a sustainable agriculture.
... The peer review history for this article is available at https://publo ns.com/publo n/10.1111/jph.12947. A sporulation index (0 -no sporulation, 1 -weak sporulation, 2moderate sporulation, 3 -dense sporulation) was calculated (Cohen et al., 2013). b Treatment differences were analysed via ordinal logistic regression. ...
Opium poppy, belonging to the family Papaveraceae, is grown for its alkaloid compounds of pharmaceutical value. Downy mildew caused by Peronospora somniferi and Pe. meconopsidis, substantially impacts crop production. The present study was conducted to identify the host range of Pe. somniferi and Pe. meconopsidis within selected weed and ornamental members of the Papaveraceae family. Nine Papaver spp., Meconopsis cambrica and a nonhost control (tomato, Solanum lycopersicum) were challenged with both pathogens under controlled glasshouse or laboratory conditions using infested soil or foliar applied sporangia as inocula. Peronospora somniferi and Pe. meconopsidis induced disease symptoms, including sporulation, in at least one trial for all tested species except for Pa. atlanticum and tomato. Species‐specific PCR testing of foliage of challenged plants confirmed infections by both pathogen species of symptomatic plants, identifying these as hosts. Positive PCR tests were also obtained from Pa. atlanticum plants for both pathogens. However, in the absence of pathogen sporulation structures as further evidence of infection, the host status of Pa. atlanticum remains inconclusive. Testing of seeds collected from Pe. somniferi and Pe. meconopsidis infected plants of Pa. somniferum, Pa. dubium, Pa. rhoeas and Pa. nudicaule showed presence of both pathogens, indicating likely ability for seed transmission in these species. We identified new hosts of these pathogens and discuss potential implications of these alternative hosts in pathogen survival, dissemination and epidemic initiation.
... Sporulation occurs in moisture saturated atmosphere at an appropriate temperature and often during the night, in the dark and in chlorotic lesions 5-15 days old [41]. In controlled greenhouse experiments, sporulation occurs 6-7 days post inoculations [37]. ...
... During the first 6 h, hyaline sporophores are formed and as they emerge from stomata gradually become dichotomously. In the subsequent 5 h, dark spores are produced on the tips of the sporophore branchlets (sterigmata) [41]. The light strongly inhibits spore formation, but not sporophore development and emergence through leaf stomata. ...
... The light strongly inhibits spore formation, but not sporophore development and emergence through leaf stomata. Yet, sporophores formed under the light are abnormal and unable to form spores. Cohen et al. in 2013 discovered that lightning during the second half of the night inhibits spore formation, and narrow band led illumination showed that red light (λmax 625 nm) was most inhibitory to spore formation comparing to blue light (λmax 440 nm) while in other oomycetes is quite the opposite [41]. They speculate that probably P. belbahrii has a different photoreceptor sensitive to red light. ...
... Peronospora belbahrii sporulate at night (Yarwood, 1937); however, sporulation can be inhibited if DM-infected leaves are exposed to sufficient amounts of broadband (Cohen et al., 1978;Yarwood, 1937) or narrowband light spectra (Cohen, 1976;Cohen et al., 2013;Patel et al., 2016) at night. Continuous nighttime light exposures ranging from 3.7 to 240 mmol · m -2 · s -1 have been shown to inhibit sporulation on DM-infected leaves (Cohen, 1976;Cohen andEyal, 1977, 1980;Cohen et al., 1978Cohen et al., , 2013Nordskog et al., 2007;Patel et al., 2016). ...
... Peronospora belbahrii sporulate at night (Yarwood, 1937); however, sporulation can be inhibited if DM-infected leaves are exposed to sufficient amounts of broadband (Cohen et al., 1978;Yarwood, 1937) or narrowband light spectra (Cohen, 1976;Cohen et al., 2013;Patel et al., 2016) at night. Continuous nighttime light exposures ranging from 3.7 to 240 mmol · m -2 · s -1 have been shown to inhibit sporulation on DM-infected leaves (Cohen, 1976;Cohen andEyal, 1977, 1980;Cohen et al., 1978Cohen et al., , 2013Nordskog et al., 2007;Patel et al., 2016). ...
... Considering the energy efficiency improvements available with many horticultural LED luminaires relative to the incumbent HID systems, they may also be cost-effective for controlling basil DM sporulation at night. Indeed, previous studies have shown that continuous nighttime exposures to broadband and narrowband spectra ranging from 3.7 to 240 mmol · m -2 · s -1 can suppress DM sporulation (Cohen, 1976;Cohen et al., 1978Cohen et al., , 2013Cohen and Eyal, 1977;Nordskog et al., 2007;Patel et al., 2016). These continuous nighttime light levels can further increase basil yields in healthy plants (Patel et al., 2018). ...
Lighting from red and blue light-emitting diodes (LEDs) is common for crop production in controlled environments. Continuous application of red or blue light at night has been shown to suppress sporulation by Peronospora belbahrii , the causal organism of basil downy mildew (DM), but the suppressing effects of intermittent applications of red and blue LEDs have not been thoroughly researched. This study examined the effects of red (λ max = 670 nm) and blue (λ max = 458 nm) LED top lighting, at two photosynthetic photon flux densities ( PPFD = ≈12 and ≈60 µmol·m ⁻² ·s ⁻¹ ), using continuous (10-hour) nighttime and two intermittent nighttime exposures, to suppress basil DM sporulation. The two intermittent treatments consisted of one 4-hour exposure and three 1.3-hour exposures spaced 3 hours apart. Continuous nighttime treatments with blue or red LED top lighting at ≈60 µmol·m ⁻² ·s ⁻¹ were able to suppress basil DM sporulation by more than 99%. At a given nighttime dose of light that did not completely suppress sporulation, continuous lighting was more effective than intermittent lighting, and for these partially suppressing doses, red LEDs were not significantly different from blue LEDs for suppressing sporulation. The present study showed that horticultural lighting systems using red and blue LEDs to grow crops during the day can also be used at night to suppress basil DM sporulation by up to 100%.
