Journal of Phytopathology最新文献

Dieback disease is one of the constraints to cocoa production in Indonesia. A newly identified dieback symptom has been observed in cocoa farms in East Luwu since 2015 and later observed in Luwu, Pinrang, Enrekang and Soppeng Regency, South Sulawesi. The potential causal agent identity was determined using morphological characteristics, DNA sequences, and phylogenetic analyses. A total of four fungal isolates out of seven isolates that were recovered from diseased stems morphologically resembled Lasiodiplodia species. ITS and EF1α sequencing confirmed that three of the Lasiodiplodia isolates were Lasiodiplodia theobromae, and one isolate was Lasiodiplodia pseudotheobromae. The aggresiveness of all fungal isolates and control was further determined by a leaf disk assay. Experiments showed that L. theobromae isolate CAS0321 was the most aggressive isolate in a leaf disk assay, while other Lasiodiplodia isolates, Fusarium isolates and Diaporthe isolate, were less aggressive. L. theobromae isolate CAS0321 was further used for a pathogenicity test on cocoa seedlings. Two months after inoculation, L. theobromae isolate CAS0321 caused elongated streaks on seedling stems with dark brown to black streaking of vascular tissues similar to that observed in natural infections. This is the first report of a virulent isolate of L. theobromae associated with cocoa dieback in Sulawesi.

Pestalotiopsis guepinii is a pathogenic fungus that causes grey blight on Camellia pitardii. In this study, we investigated the enzyme activity and kinetics of these cell-wall-degrading enzymes (CWDEs) produced by Pestalotiopsis guepinii in both C. pitardii leaves and culture medium. Our enzyme activity experiments revealed that the activities of xylanase, pectin methyl-galacturonase (PMG), β-1,4-endoglucanase (Cx), and β-glucosidase were high in both C. pitardii leaves and culture medium. These enzymes played a significant role in the pathogenic process. However, the activity of laccase was found to be very low and had a minor impact on the pathogenic process. Furthermore, our enzyme dynamics experiments demonstrated that the optimal reaction temperature for PMG and Cx was 50°C, while for β-glucosidase and xylanase, it was 60°C. The optimal reaction pH for Cx, β-glucosidase, and xylanase was 5.0, whereas for PMG, it ranged from 5.0 to 6.0. This indicates that these four enzymes prefer acidic conditions. Moreover, we observed that the activities of Cx, PMG, and xylanase decreased with increasing reaction time. On the other hand, the activity of β-glucosidase initially increased sharply and then decreased slowly. The maximum reaction rates of the four cell-wall-degrading enzymes were ranked as follows: xylanase > PMG > β-glucosidase > Cx. Additionally, the affinities of these enzymes with substrates were ranked as follows: PMG < Cx < xylanase < β-glucosidase.

In late summer 2022 and 2023, powdery mildew symptoms were found on female plants of hemp (Cannabis sativa) growing in a private garden in Hradec nad Moravicí (Silesia, Czech Republic). On the upper sides of the leaves, white powdery colonies were observed which coalesced and finally covered the whole leaf surface. The stems and flowers were not affected. Microscopic examination revealed the formation of asexual (anamorphic) states characterized by conidiophores forming catenescent conidia (Euoidium type), but with two types of conidia, viz., ellipsoid to ovoid or doliiform conidia with fibrosin bodies (resembling conidia of Podosphaera spp.), and ellipsoid to doliiform conidia without fibrosin bodies (resembling conidia of Golovinomyces spp.). Molecular genetic analyses confirmed co-infections in the studied hemp samples by two powdery mildew species, viz., Podosphaera macularis and Golovinomyces ambrosiae, which represent first records from the Czech Republic, as well as Europe and in the world. The authors discuss the latest information and ideas regarding this pathosystem.

Phelipanche aegyptiaca (Pers.) Pomel, commonly known as Egyptian broomrape, is an obligate root parasite, infesting solanaceous crops mainly in Mediterranean countries. Certain antagonistic fungi could be effectively used as a biocontrol agent for this parasitic plant. In this study, three fungal isolates (F1, F2 and F3) were obtained from P. aegyptiaca seeds covered with mycelium. The isolates were characterized based on morphological features and ITS and TEF sequence analysis. They were classified as belonging to Fusarium fujikuroi with a sequence similarity of 99.80% and 100%, respectively. The pathogenicity of the isolates on P. aegyptiaca and tomato were determined. In a P. aegyptiaca seed assay, all isolates allowed seed germination with delayed radicle development. Disease severity among the isolates ranged from 40%–70% on the basis of radicle necrotic area. The F1 isolate caused more than 40% disease on the spiders and tubercles in a polyethylene bag assay. The average of the total of spider and tubercle mortality caused by the F1 isolate was 63.5% at 9 days after inoculation. Moreover, the F1 isolate was considered non-pathogen on tomato with 6.66% disease severity after root inoculation. To the best of our knowledge, this is the first report of F. fujikuroi on P. aegyptiaca seed. Pending further development, the F1 isolate could have potential for the biocontrol of P. aegyptiaca in the future.

Colletotrichum truncatum, the predominant fungal species associated with soybean anthracnose, is responsible for significant losses in this crop. Chemical control via fungicide application is the most effective strategy for the control of soybean foliar diseases. However, the increasing incidence of anthracnose in some regions of Brazil indicates that current chemical control is not effective against anthracnose. In this study, we evaluated the fungicide sensitivity of C. truncatum genetic lineages to the fungicides azoxystrobin, thiophanate-methyl, difenoconazole, and fludioxonil using isolates representing two important regions of soybean production in Brazil. We characterized the molecular resistance to the quinone-outside inhibitors (QoI), methyl benzimidazole carbamates (MBC), and demethylation inhibitor (DMI) fungicide groups based on amino acid sequences of the cytochrome b (cytb), β-tubulin gene (β-tub), and P450 sterol 14a-demethylases (CYP51) genes. Multiple resistance of C. truncatum isolates to QoI and MBC was observed associated with mutation points in the β-tub (E198A and F200Y) and cytb (G143A). Alternatively, low EC₅₀ values were found for fludioxonil and difenoconazole indicating high efficacy. Analysis of C. truncatum genomes revealed two potential DMI targets, CYP51A and CYP51B, and higher genetic variability in the CYP51A gene. A positive correlation was found between genetic differentiation of C. truncatum populations and fungicide sensitivity (Student's t-test <0.001). To our knowledge, this is the first report of multiple resistance to QoI and MBC fungicides in C. truncatum in Brazil.

Traditionally, apricot trees suffering from bacterial canker disease caused by Pseudomonas syringae pv. syringae were treated in orchards through the application of antibiotics or copper-based drugs. However, considering the disadvantages of the long-term use of chemical pesticides and antibiotics, there has been an increasing interest in phages, which have a lytic effect on bacteria, as biopesticides in recent years. In this study, we conducted a comprehensive examination of phage TE, isolated from wastewater in Turkey, from this perspective. Through scanning electron microscopy and phylogenetic analysis, we classified phage TE as belonging to the order Caudovirales and the family Strabovoridae. The phage TE exhibited a robust host lysis efficiency, with 280 infectious phage particles produced per bacterial cell in just 15 min. In experimental trials, treatment with phage TE resulted in an impressive 82% inhibition of bacterial canker disease in apricot leaves, highlighting its effectiveness as a phage therapy agent. Furthermore, phage TE exhibited long-term stability when stored at 4°C without cryoprotectant and displayed tolerance to a wide temperature (−20°C to 50°C) and pH (2–12) range but its tolerance to UV-C was very low. The genome and bioinformatics analyses of P. syringae phage TE have identified distinct protein level differences between other phages of the same species, despite sharing similarities at the nucleotide level. These findings suggest the potential use of phage TE as a biocontrol agent, offering a promising solution to control apricot bacterial canker.

Pink root disease (PRD) caused by Setophoma terrestris is a major disease in onion-producing regions. The fungus primarily infects onion, but occasionally causes disease on other plant species such as cereals, corn, cucurbits, pepper, spinach, and soybean. In this study, we analysed the efficacy of three commercially available fungicides at low dose in two successive years (2020–2021) in the field. These included Priaxor Xemium Brand (fluxapyroxad + pyraclostrobin) at 1.0 or 1.5 L/ha, Lamardor 400 FS (propiconazole + tebuconazole) at 2.5 kg/ha, and Rovral TS (iprodione) at 5.0 kg/ha applied via soil surface irrigation, and also Priaxor as foliar application (1.0 L/ha) against PRD on three onion cultivars: white, red, and yellow. All fungicides were applied thrice within 3-week intervals from the onset of PRD (mid-February), and fungicidal efficacy was determined 2 weeks prior to harvest (mid-May). The lowest PRD severity was recorded for Priaxor 1.5 L/ha at 9.5%, followed by Lamardo at 10.1%, and the remaining treatments compared with the untreated control at 47.7% severity. The highest production (per 100 bulbs) was recorded for Priaxor 1.5 L/ha with 7.36 kg, followed by Lamardo with 6.86 kg and the remaining treatments compared with untreated at 4.33 kg. When treatment effects on soil enzymes were examined prior to harvest, there was no substantial change in urease activity, whereas soil application of Priaxor increased alkaline phosphatase activity by 50% and decreased acidic phosphatase by 42% compared with the untreated control. Our data indicated that fungicides have subtle differences in efficacy profiles, which may translate to improved management against PRD.

Cassava mosaic disease (CMD) causes significant losses in cassava production in Africa. The disease is caused by several cassava mosaic geminiviruses (CMGs) and spread through the use of infected plant materials. The infected plants remain infected throughout their vegetative lifecycle as the disease cannot be controlled by standard plant protection measures. Therefore, it is important to develop inexpensive field-based methods that can be easily adopted by small-scale farmers to sanitize geminiviruses-infected stem cuttings used as planting material. This study aimed at eliminating CMGs from infected cassava stem cuttings by use of salicylic acid (SA), hydrogen peroxide (H₂O₂) and hot water (HW) treatments. Eight varieties of CMD-infected stem cuttings were pretreated with SA (1.25, 2.5 and 5 mM), H₂O₂ (0.5%, 1.0% and 1.5%) or hot water (50 and 55°C) at different exposure times before establishment in the glasshouse for evaluation of subsequent plant growth and geminivirus detection. Based on the cassava varieties used for the different treatments, treatment with hot water at 50°C for 5 min and 1.0% H₂O₂ for 12 h were the most effective in eliminating CMGs with an efficiency of 81.7% and 77.8%, respectively. Salicylic acid at a concentration of 5 mM for 6 h eliminated the viruses in 65.1% of the cuttings. The methods tested herein have the potential for producing planting materials with significantly reduced CMD risk for smallholder farmers and the cassava industry to meet their increasing demand. It could also contribute to the global exchange of germplasm for conservation and breeding programs.

Two members of the Araceae broadly cultivated as ornamentals, namely Epipremnum aureum (common name golden pothos or, in Brazil, jiboia) and Zantedeschia aethiopica (common name arum lily or, in Brazil, copo-de-leite), were observed bearing Cercospora leaf spots. The former is a very common garden plant, whereas the latter is an important crop for the flower industry. An examination of the fungus associated with the disease on each plant revealed a very similar morphology which suggested that those might be conspecific. A polyphasic taxonomic study, including phylogenetic analyses based on act, cal and his3 sequences, was conducted. Both isolates from the two aroids were found to belong to the Cercospora apii complex, but were genetically distinct. Cercospora sp. Q was identified as the etiological agent of the leaf spots on E. aureum, whereas the fungus on Z. aethiopica was found to belong to Cercospora sp. G. Inoculations confirmed the pathogenicity of both isolates to their original hosts, and cross-pathogenicity assessments revealed that both isolates were capable of infecting both E. aureum and Z. aethiopica. The limited morphological and pathological distinction between the fungi on these two hosts reflects the continued difficulty in the taxonomic treatment and species delimitation for Cercospora sp. G, Cercospora sp. Q, as well as other provisional code-based Cercospora spp., and other components of the broad C. apii s. lat. complex. The name Cercospora richardiicola (as C. richardiaecola) was mistakenly used for the fungus on Z. aethiopica in earlier publications and this has been corrected herein.

Corynespora leaf fall disease caused by the fungus Corynespora cassiicola is a major leaf disease of Hevea brasiliensis, the commercial source of natural rubber. Different clones of H. brasiliensis show varying levels of sensitivity towards different strains of C. cassiicola. The genetic mechanism behind the differential sensitivity of H. brasiliensis clones has to be identified in order to develop clones resistant to wider range of C. cassiicola strains. The available information on the sensitivity of H. brasiliensis clones is based on the observation of natural infection or infection of detached leaves. In the present study, the sensitivity of seven H. brasiliensis clones towards two strains of C. cassiicola belonging to two different races was determined using a more precise method by artificial infection of the plants under controlled conditions. Strain CLN 16 was found to be more virulent compared with CSB 16, as it induced more severe symptoms in a shorter period. Among the four different stages of leaves, Stage II leaves with copper brown to apple green colour showed higher sensitivity to both strains followed by Stage III leaves with apple green appearance. Among the clones, RRIM 600 had a higher susceptibility towards CSB 16; however, it was the most resistant clone towards CLN 16. Clone PB 350 showed the highest susceptibility towards CLN 16 whereas RRIM 928 showed the highest resistance towards CSB 16. The present study provides a platform for further studies leading to the development of H. brasiliensis clones with resistance towards wider range of C. cassiicola strains.