European Journal of Plant Pathology最新文献

Abstract

Fusarium wilt, caused by Fusarium oxysporum f. sp. passiflorae (FOP), stands out as an obstacle to the production of Passiflora edulis Sims. Little is known about the interaction of FOP with substrates and pH ranges that can be used in the development of management strategies or selection for resistance in Passiflora spp. Thus, the effect of different soil: manure or soil: coconut fiber ratios with pH ranging from acidic to alkaline on the production of FOP propagules was evaluated. The experiment was carried out in a completely randomized design, using four soil: manure or soil: coconut fiber ratios (5:0, 5:2, 5:4, 5:6 (v:v)). Each mixture’s pH was adjusted from 4.2 to 8.0 (soil: manure) or 4.2 to 9.7 (soil: coconut fiber). The production of microconidia, macroconidia, chlamydospores and colony forming units was evaluated at 3, 7, 14, 21 and 28 days after substrate infestation. The greatest number of propagules was registered in the groups treated with the highest proportions of manure or coconut fiber. The use of manure, regardless of the pH range, provided increases of 98%, 48%, and 13% in the number of colony forming units, microconidia and chlamydospores, respectively, in relation to the spores produced in substrates using coconut fiber. However, the production of macroconidia was 66% higher when fiber was used. Chlamydospore production was not affected by substrate pH, unlike other propagules with greater activity at slightly acidic, neutral or alkaline pH. The use of soil plus cattle manure in the ratios 5:4 or 5:6 with a pH between 5.1 and 8.0 was associated with the highest production of FOP propagules.

Essential oils (EOs) are plant natural products typically composed of a complex mixture of molecules, many of them recognized for their antibacterial potential. EOs have different benefits in contrast to synthetic agrochemicals, like no persistence on the environment, compatibility with classical biocontrol agents and natural enemies, and no toxicity for most non-target organisms. The aim of this work was to evaluate the antibacterial effect of lemon (Citrus limon) and orange (Citrus sinensis) EOs and their combinations with mint (Mentha x piperita) or oregano (Origanum vulgare) EOs against Streptomyces scabiei, the main causal agent of the potato common scab. The EOs were characterized by GC-MS. The antibacterial activity of citrus EOs and combinations were evaluated using the broth microdilution method and the effect of the EOs on the S. scabiei envelope was analyzed by scanning electron microscopy. The lowest EO antibacterial concentrations were obtained for the combination of lemon and mint EOs, mixed in equal quantities. The application of this combination of lemon EO on S. scabiei cultures caused cell envelope damage, causing changes in the superficial hyphae anatomy and narrowing their thickness. Additionally, orange EO efficacy was enhanced in combination with oregano EO, suggesting that this binary mixture could improve their utilization as bactericidal agents against S. scabiei. These results position citrus EOs and some of their combinations as promising sustainable alternatives for potato common scab control.

South Africa is the largest producer of macadamias in the world, producing an estimated 61,288 tons nut-in-shell in 2022. In order to ensure the sustainability of the industry, it is important that research focuses on the control and eradication of economically important pests and diseases. Macadamia trees in the Mpumalanga Lowveld of South Africa have for some time shown severe chlorosis, which coincides with a significant drop in production, with losses of up to 60% being recorded. The disease has since been coined Macadamia Chlorosis Disease (MCD). In an attempt to determine whether MCD may be associated with a virus, high-throughput Illumina sequencing was performed on RNA extracted from both diseased and healthy trees collected from farms in Mpumalanga. Subsequent data analyses could not link a specific virus to MCD, however, reads spanning the full genome of a novel virus belonging to the Orthotospovirus genus were obtained. An RT-PCR assay was optimized for the detection of this virus and subsequent surveys linked the virus to ringspot symptoms which are commonly observed on different macadamia cultivars. The virus has to date been identified from orchards in Mpumalanga, Limpopo and KwaZulu-Natal. Other viruses described in the genus are known to cause severe crop losses and it is therefore important that the virus, provisionally named macadamia ringspot-associated virus (MRSV), be further studied to determine whether association with this virus can lead to yield losses, and whether appropriate control strategies must be implemented to prevent the spread of MRSV.

Abstract

Botrytis cinerea is the causal agent of gray mold disease affecting Paeoniaceae plants. The present study focuses on the potential of Bacillus amyloliquefaciens Mdgb15 as a promising biological control agent toward B. cinerea. The strain Mdgb15 showed the highest inhibition rate (55.56%) among all the strains tested against B. cinerea growth and was effective in controlling tree peony gray mold in detached leaves. A conventional PCR with three specific primer pairs detected lipopetides substance synthesis genes of Mdgb15. The results revealed that Mdgb15 had srfAA, fenA and ituD genes, which resulted in the production of surfactin, fengycin and iturin. An accurate qRT-PCR protocol with specifically designed primers was developed to characterize the expression of lipopeptide synthesis gene of Mdgb15. The qRT-PCR analysis revealed that the expression of the ituD and fenA genes in Mdgb15 was significantly up-regulated during the coculture with B. cinerea. Subsequently, the lipopeptides were extracted by acid precipitation of culture filtrate of Mdgb15 and were separated by Sephadex Gel chromatography. Three separated fractions exhibited strong antifungal activity against B. cinerea, and were identified as bacillomycin D by MALDI-TOF-MS analysis. This study has demonstrated that B. amyloliquefaciens Mdgb15 is a future potential new biocontrol agent for controlling tree peony gray mold disease. It suggests that the antifungal mechanisms of Mdgb15 may be at least partially associated with its ability to secret bacillomycin D.

Production of volatile organic compounds (VOCs) is one of the modes of actions of Trichoderma spp. They inhibit pathogenic fungi/bacteria, promote plant growth, and also affect interactions of plants with pathogens. However, the study of VOCs emitted by Trichoderma species associated with olive roots and its benefits are still limited. In the present study, two strains of Trichoderma collected from olive grove soil were evaluated for their antagonistic activity against five strains of Verticillium dahliae named (Vd1 to Vd5) by indirect confrontation assay. In addition, identification and quantification of volatile compounds produced by each strain were assessed through gas chromatography-mass spectrometry (GC–MS). The extraction of metabolites was performed from filtrates using liquid–liquid extraction. Extracts obtained were taken for analysis through GC–MS. Results of indirect confrontation assay showed a high inhibitory activity against V.dahliae. Trichoderma asperellum (T4) and Trichoderma harzianum (T12) exhibited an average inhibition rate of 64.49% and 61.59% respectively. Besides, 98 volatile compounds were detected through GC–MS analysis, including important volatile compounds with antifungal activities, such as D-limonene, octadecanoic acid methyl ester, hexadecanoic acid, toluene, phenylethyl alcohol, benzene derivatives, several phenolic isomers, citral, eicosane and 13-docosenamide. Other volatile compounds revealed antibacterial activity, providing growth promotion, or antioxidant activity, such as oleic acid. Importantly, 7-epi-nemorosone was detected for the first time as new molecule produced by Trichoderma harzianum (T12). This molecule provides anticancer and antioxidant activity. Overall, these strains with various activities are considered as excellent source for discovery of bioactive molecules with eventual application in different biological fields. However, they could be beneficial mainly for suppressing plant pathogens and stimulation of plant growth.

Xanthomonas citri subsp. citri is a plant bacterium that causes citrus canker, an important disease in several citrus-growing areas. Due to its relevance, this pathosystem has been frequently investigated, requiring suitable protocols of inoculation for symptom reproduction. This study aimed to evaluate the effect of the concentration of X. citri and the duration of the moisture chamber period on the incidence and severity of citrus canker symptoms under greenhouse conditions. Inoculum concentrations ranging from 10⁰ to 10⁸ cfu/mL were evaluated using both infiltration and spray-inoculation methods. The effect of the moisture chamber on the development of citrus canker lesions was assessed for 24 or 48 h before and/or after inoculation. The minimum concentrations required to infect 100% of the inoculated leaves using infiltration and spray-inoculation were 10⁴ and 10⁷ cfu/mL, respectively. Intermediate severity levels, e.g., 3.2 to 11.4 and 2.5 to 6.7 lesions/cm², were observed using 10³ – 10⁴ cfu/mL for infiltration and 10⁶ – 10⁷ cfu/mL for spray-inoculation. This severity level is suitable when the number of lesions in a given treatment needs to be determined. Conversely, lower or higher inoculum concentrations resulted in severities either extremely low, with no or very few lesions, or excessively high, with coalesced lesions forming a large necrotic area, respectively. A moisture chamber period of 24 h after spray-inoculation was sufficient for reproducing citrus canker lesions under greenhouse conditions. Suitable inoculum concentrations and the use of a moisture chamber after spray-inoculation of X. citri are critical for the successful reproduction of citrus canker symptoms.

Fusarium wilt of tomato is a destructive disease worldwide, causing economic losses every year. In this research, a biological method was used to control the disease. Metabolite solution of Trichoderma harzianum was used for green synthesis of zinc oxide nanoparticles (ZnO-NPs) from zinc nitrate (ZnNO₃), and GC/MS analysis of metabolite was performed. Then, the antifungal activity of the synthesized ZnO-NPs was evaluated in vitro and in vivo conditions. Results were compared to different concentrations of Iprodione+Carbendazim (Rovral-TS®) fungicide. Synthesized ZnO-NPs were characterized using ultraviolet-visible spectrometry (UV-Vis), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). UV-Vis spectra showed an intense peak at 339 nm. X-ray diffraction pattern showed the crystalline nature of the ZnO-NPs. FTIR revealed various functional groups including phenols, ketones, aldehydes, aliphatic and primary amines, nitriles, alkanes and alkynes in synthesized ZnO-NPs. The size of the ZnO-NPs was determined to be in the range of 25–60 nm. Based on atomic absorption spectroscopy, the foliar application of synthesized ZnO-NPs led to acceptable level of zinc concentration in the leaves and it can be useful to compensate zinc deficiency. Some growth factors showed relative improvement compared to the control and some of them were not significantly different. Complete inhibition of mycelia growth of F. oxysporum was observed in 100 µg/ml concentration of ZnO-NPs in vitro conditions and disease severity was significantly reduced in vivo conditions, indicating that green synthesized ZnO-NPs gave better results in low concentration than the fungicide.

Polyprobes have great potential for simultaneous multipathogen detection and have been successfully used for detecting a large number of plant viruses and/or viroids in a single assay. However, how the length of the polyprobe or the position of the corresponding single probes within them influence their sensitivity has not been previously addressed. In this study, we have developed three polyprobes with the capacity to detect 9 (poly9), 12 (poly12) or 21 (poly21) viruses representing the least prevalent common viruses, the most prevalent viruses or a combination of both types of viruses, respectively, affecting pepper crops. By using known amounts of complementary transcripts and serially diluted extracts from different individually infected pepper plants, we observed that, overall, the detection limit of poly12 and poly21 polyprobes was 5 times and 25/125 times lower than that of the single probes, respectively. An exception was the detection of cucumber mosaic virus and tomato mosaic virus, which were better detected by using poly21 than poly12, possibly due to the more central position of these two probes within the corresponding polyprobes. The analysis of 85 field samples using both poly12 and poly21 also revealed more positives samples with the former, confirming, in general, a higher detection limit for poly12 than poly21. The optimal polyprobe size and temperature for efficient polyvalent virus and/or viroid detection using this technology are discussed.

The production of chickpea, an important legume grown all over the world, is severely constrained by ascochyta blight, which can cause up to a 100% yield loss. The most reliable, economical, and effective management techniques for this disease is fungicide treatments and host plant resistance. The objectives of the present study were to evaluate chickpea varieties and fungicide application intervals against chickpea ascochyta blight epidemics; identify the most effective fungicide application time interval; and determine the association of ascochyta blight incidence and severity with yield and yield components of chickpea. The study was carried out in two hotspot regions (Dhera and Dugda) during the main growing seasons of 2020 and 2021. Three chickpea varieties (Dhera, Habru, and Mariye) and four fungicide spray schedules (Mancozeb 80% WP at a rate of 2.5 a.i. kg/ha) were utilized as treatments, and they were treated up until the crop reached full physiological maturity. Twelve treatments were set up in a factorial arrangement with three replicates using a randomized complete block design (RCBD). Both the Gompertz model and the logistic model were used to assess dependent variables under various treatments. For the disease progres rate under various treatments, the slope of the regression line was determined. The results of the data analysis revealed considerable variations between the treatments. Fungicide application time schedule, varieties, and their interactions had substantial effects on ascochyta blight. The Mariye variety had the highest incidence (100%) and severity (70.68%) of ascochyta blight, with 100% yield loss seen from untreated plots, whereas the Dhera variety experienced the lowest incidence (6.35%) and severity (11.01%) following fungicide management on the 7th day of the interval. The analysis of the means revealed that applying fungicide at intervals of 7 and 14 days was an effective strategy to reduce the severity, incidence, and AUDPC of ascochyta blight. This strategy led to the highest yield of seeds per pod, pods per plant, and grain yield when compared to the untreated plots and the plot treated at a 21-day interval. To handle polycyclic outbreaks of the disease successfully, both the logistic and Gompertz models were used. The study's extent of variety resistance was enough to control the disease in two cropping seasons and locations. This investigation led us to the conclusion that a program to control ascochyta blight of chickpea in Ethiopia may include the integration of fungicides and resistant varieties. Additionally, methods for integrated management of the Ethiopian ascochyta blight on chickpeas must be developed.

Huanglongbing (HLB) is a devastating citrus disease that causes significant financial losses in the citrus industry. However, there is no cure by current control strategies. Damaged soils were observed in citrus orchards; root lesions and nematodes were observed in HLB-affected citrus tree roots. Bacillus subtilis (B. subtilis) makes a great contribution to pathogen control and has the potential to control HLB. Purpureocillium lilacinum (P. lilacinum) and Trichoderma harzianum (T. harzianum) can kill pathogenic organisms such as nematodes and Phytophthora spp. to protect roots. Restoration of the damaged soils and improvement of citrus root growth through the introduction of soil amendments and biocontrol agents (containing B. subtilis, P. lilacinum, and T. harzianum) may provide an efficient approach to controlling HLB. Results revealed that soil properties such as soil pH and organic matter content were improved. After three months of combination treatment of soil amendment and biocontrol agent through root drenches, the citrus grew new roots and its leaves changed from yellow to green. The percentage of HLB-positive citrus trees—Orah, Tangerine, and Navel Orange—decreased from 90 to 0%, 87.5% to 21.88%, and 81.25% to 0% over three years, respectively. Furthermore, the productivity of HLB-affected orchards was restored, and both production and quality saw significant improvement. These results suggested that combining soil remediation and biocontrol improved soil quality and protected citrus root growth, thus effectively controlling HLB.