Journal of Plant Pathology最新文献

Several fungicide products with metalaxyl-chlorothalonil as the active ingredients are available in the Mexican market. Applying products containing this mixture of molecules is a common method that farmers choose to prevent damage caused to crops by Phytophthora capsici. Despite the efficacy of the mixture of metalaxyl-chlorothalonil in controlling the growth of this pathogen, their intensive use could contribute to the development of multidrug-resistant strains. Additionally, the dynamics of resistance to commercial metalaxyl-chlorothalonil-based fungicides and the virulence of P. capsici during continuous exposure are yet to be studied in detail. In this study, four continuous generations of P. capsici were exposed to two concentrations (5 and 100 μg·mL⁻¹) of a commercial fungicide containing metalaxyl-chlorothalonil as the active ingredients. Changes in morphology, growth, and virulence were observed after the first interaction with the fungicide. However, in further generations exposed to the same amount of the product, the morphology and growth of P. capsici were partially restored, whereas its virulence was completely re-established. These results indicate a rapid adaptation to the metalaxyl-chlorothalonil mixture and highlight the importance of using different methods to control P. capsici and prevent the development of more virulent and multidrug-resistant strains.

One of the most well-known vegetables used by the majority of the population worldwide, known as tomato (Solanum lycopersicum), is affected by wilt disease caused by Fusarium oxysporum f. sp. lycopersici (FOL), mainly in the tropics. In the current scenario, a residue-free management approach using a biological control agent is being explored to address the invasion of phytopathogens. This investigation assessed the ability of Trichoderma asperellum (Tv1) to reduce pathogen growth and promote plant growth. A dual culture assay demonstrated that Trichoderma asperellum Tv1 inhibited the growth of the pathogen mycelia by up to 79.63%, and volatile organic compounds (VOCs) emitted by the antagonist inhibited FOL to a maximum of 61.48% of the MGI. An oil-based (OB) formulation was developed using a spore suspension of Tv1 with improved shelf life (3.22 × 10⁸ cfu/ml on the 120th day). Compared with those in the control treatment, significant improvements in vegetative parameters such as germination percentage (100%), root length (8.12 cm) and shoot length (5.58 cm) were observed by the roll towel method upon seed treatment (5 ml/kg) with the OB formulation. There was a minimum wilt disease incidence in tomatoes, up to 19.34% (T8), which was recorded in comparison with that in the inoculated control (T12) (64.75%). Overall, Trichoderma asperellum Tv1 was proven to be an effective biocontrol agent against Fusarium wilt disease in tomato. This study revealed a reduction in mycelial growth of the pathogen caused by mycoparasitism and VOCs under laboratory conditions and wilt disease incidence in a glasshouse study in response to treatment with the biocontrol agent Tv1. With this viewpoint, this approach could be considered a promising environmentally safe approach for managing wilt disease in tomatoes.

Since the beginning of 2023, an outbreak of Fusarium wilt-like symptoms on lettuce (Lactuca sativa L.) has been observed in Lam Dong province, Vietnam. Wilting consistently combined with yellow leaves, root rot and stunted growth are common symptoms of infected plants. Thirty-one fungal isolates were recovered from symptomatic lettuce plants and identified based on morphological and molecular characteristics (rDNA internal transcribed spacer (ITS) and the translation elongation factor (TEF-1α) gene sequences) as F. oxysporum (51.6%), F. incarnatum-equiseti species complex [FIESC: F. compactum (16.1%) and F. sulawesiense (3.2%)], and Plectosphaerella cucumerina (29.0%). The composition of these fungi varied between locations, with co-infection by P. cucumerina and Fusarium spp. observed in lettuce plants from the same field. Pathogenicity tests showed that all isolates were pathogenic to lettuce, causing reduced seed germination, induced collar rot, and decreased seedling survival and mass. Notably, F. oxysporum isolates caused collar rot earlier, significantly reducing seedling survival and indicating faster disease progression than P. cucumerina and FIESC. Additionally, there was wide variation in virulence and specialization of isolates at different stages of seedling growth: P. cucumerina L0311 primarily reduced seed germination, while F. oxysporum L0911 and L0331 strongly inhibited seedling growth. These findings suggest a shift in the pathogenic roles of the isolates during seed germination and seedling growth, with potential variation continuing post-nursery. This work is the first to report on the population and virulence profile of fungi causing lettuce wilt in Vietnam, providing essential insights for quarantine measures, disease monitoring, and management strategies.

The virulence spectrum of leaf rust of barley (Puccinia hordei Otth.) has not been studied in India so far. This is a first study to design a system of pathotype nomenclature and know the virulence structure of pathotypes of P. hordei in India. All the available near-isogenic lines (NILs) of Rph genes, lines with known Rph genes, and other barley accessions including promising Indian barley cultivars were screened using 328 P. hordei isolates from different parts of India, Bhutan, and Nepal. Using a binomial system of nomenclature, 11 distinct pathotypes of P. hordei occurring in India were identified and named. A grouping of pathotypes in the 328 leaf rust samples analyzed since 1999, it was evident that pathotype H2 followed by H3, H7, H4 and H1 were the most predominant pathotypes. Based on the molecular studies, all the pathotypes were distinct and fell into three groups (A, B, and C). Group A further clustered into two subgroups A1 (4 pathotypes) and A2 (2 pathotypes). The virulence phenotype and molecular genotype based distinction of P. hordei pathotypes will help in the precise screening of barley germplasm and the identification of rust-resistant lines. The establishment of an Indian differential system for the designation of P. hordei isolates will also help in monitoring the shift in virulence patterns, predominance, and emerging of new pathotypes in the future and will help scientists of other countries to make comparisons with their virulences.

The complete nucleotide sequence of a Chinese isolate C12B1 of grapevine Pinot gris virus (GPGV) from a ‘Beta’ grapevine was determined by small RNA sequencing. The size of the C12B1 genome was 7259 nucleotides (nt) without the poly (A) tail. Sequence identities of C12B1 with other GPGV isolates ranged from 79.13 to 97.52%. Phylogenetic analysis based on complete genome sequences of the global GPGV isolates indicated GPGV isolates are divided into three major groups and five subgroups within group 3, with the C12B1 isolate felled within subgroup 3a of group 3. Moreover, an infectious cDNA clone of the GPGV isolate C12B1 was generated using the seamless assembly approach. The infectious clone was then inoculated to Nicotiana occidentalis 37B and grapevine plants. Inoculated Nicotiana plants showed leaf chlorotic mottling symptoms and RT-PCR and transmission electron microscopy analysis confirmed successful infection. Additionally, the inoculated Beta grapevine plants also exhibited mild chlorotic mottling and ring spot symptoms. This study represents the first complete genome sequence of GPGV in China and the successful production of an infectious cDNA clone of a divergent GPGV isolate. These findings are a foundation for further research on the interaction between GPGV and its plant hosts.

Sugarcane white leaf disease associated with sugarcane white leaf (SCWL) phytoplasma is an important disease in sugarcane resulting in significant losses in production in Asian countries including the major regional producing countries of India and Thailand. In this study the morphological and biochemical traits in SCWL phytoplasma infected sugarcane plants, both asymptomatic (AS) and symptomatic (S1-S3) and their corresponding to phytoplasma loads, were investigated. This study found that as symptom development progressed, cane statues including plant height, leaf length, and leaf width, were reduced and corresponded with declines in both chlorophyll and dietary fiber content. Total soluble solids (TSS) were less in AS cane plants, being 16.83 ± 1.0 °brix compared to 20.58 ± 1.6 °brix in healthy plants, declining further with the progression of symptoms. This feature could be potentially used in the identification of AS sugarcanes. Phytoplasma titres increased from 2.36E + 05 copies/µg plant DNA in AS infected leaves, peaking at 1.20E + 08 copies/µg plant DNA in S3 infected leaves, before declining in severely (S4) infected leaves. AS infected plants also exhibited a peak in total phenolic compounds. By tracking the development of symptoms in sugarcane white leaf disease and the corresponding increases in titres of SCWL phytoplasma, decline in chlorophyll and dietary fiber, decrease in TSS, and a peak in total phenolic compounds at the asymptomatic stage, this study confirmed that SCWL phytoplasma significantly impacts the sugarcane host plants as early as the AS stage, this stage is potentially the focus point for early detection and interventions for controlling proliferation SCWL disease.

Cowpea is subject to attacks by a wide range of plant pathogens including bacteria, fungi, viruses, and nematodes. In this study, a field survey was conducted in cowpea growing regions of El-Minya Governorate of Egypt including Minya, Beni Mazar and Maghagha districts for leaf and pod spot disease. Our results revealed that the disease was present in all surveyed fields with the highest disease incidence and severity found in Minya District. For the first time in Egypt, the causal agent of the disease was determined to be Periconia igniaria based on morphology of the fungal isolates, internal transcribed spacer sequence homology to a P. igniaria strain, and fulfillment of Koch’s postulates. To explore control measures, zinc oxide (ZnO) and magnesium oxide (MgO) nanoparticles (NPs) were synthesized biologically using green coffee extract. Both NPs were characterized, and their formulations confirmed using scanning electron microscopy and the energy spectrum dispersion analysis. The biosynthesized ZnO- and MgO-NPs were demonstrated to have antifungal activity against in vitro mycelium growth of P. igniaria at all tested concentrations from 25 to 200 ppm, and ZnO NPs were more effective than MgO NPs at the same concentration. When 100 ppm of ZnO NPs was tested in planta, it significantly reduced disease incidence and severity in detached cowpea leaves and pods under laboratory conditions, and in cowpea plants under greenhouse conditions. Our results demonstrated that the biosynthesized ZnO NPs have great potential to be developed into an effective and eco-friendly control method against cowpea disease caused by P. igniaria.

Penicillium digitatum Sacc is a common postharvest pathogen affecting lime fruits. It causes significant losses in postharvest lime production. An emerging alternative to chemical control is the use of environmentally friendly such as edible and biodegradable films and packaging. The goal of the current study was to test different concentrations of Aloe vera gel (5, 15, 25, 50, 75, and 100% v/v), tea tree oil coating (0.5, 1, 2.5, 5, and 10% v/v), and their combination for controlling P. digitatum in vitro. The results revealed that specific concentrations of Aloe vera gel (75% and 100% v/v), tea tree oil (2.5, 5, and 10% v/v), and Aloe vera gel (25%) + tea tree oil (1%) v/v showed the highest inhibitory effect against the pathogen. The most effective concentrations of Aloe vera gel (75%), tea tree oil (2.5%), and Aloe vera gel (25%) + tea tree oil (1%) were evaluated against the green mold disease of lime under natural infection through storage period (0, 7, 14, 28 days). Compared to the control group, all edible layers demonstrated a significant delay and reduced in disease severity percentage throughout the storage periods. However, coating lime fruits with a combination of Aloe vera gel (25%) + tea tree oil (1%) successfully prevented the green mold disease of lime fruits over 28 days. The impact of these coatings was evaluated on lime fruit quality maintenance (weight loss, firmness, juice weight, total soluble solids, total acidity, pH, vitamin C, lipid peroxidation content, total phenols, total flavonoid, and total protein) over 28 days of storage during the 2021 and 2022 seasons. All treatments improved fruit quality through the storage period compared with untreated fruits. Treated lime fruits with Aloe vera gel (25%) + tea tree oil (1%) exhibited slight reductions in weight loss and juice weight compared to alternative treatments as an average of the two successive seasons. Simultaneously, this treatment improved fruit firmness, vitamin C levels, total phenols, total flavonoid, and total protein when contrasted with other treatments as an average of the two studied seasons. These findings show that the combination of Aloe vera gel and tea tree oil coatings enhances the shelf life and maintains the quality of lime fruits. They can also be used as an environmentally acceptable, chemical-free alternative treatment to preserve the postharvest quality of lime fruit.