Australasian Plant Pathology最新文献

In Qinghai Province, China, the wild rose (Rosa multiflora Thunb) has been identified as a critical host for a virulent strain of Diaporthe eres, which is implicated in the causation of the catastrophic black mold disease. A plant specimen, manifesting intense symptoms indicative of black mold, underwent a meticulous diagnostic process. Employing a combination of morphological assessments and nucleotide sequencing of key genetic markers—Internal Transcribed Spacer (ITS), Translation Elongation Factor 1-α (TEF1-α), Tubulin 2 (TUB2), Histidine biosynthesis (HIS3), and Calmodulin (CAL)—the pathogenic fungus was unequivocally identified as Diaporthe eres. The reisolation of this strain, adhering to the principles of Koch’s postulates, substantiated its etiological role in the black mold disease affecting wild roses. This study represents the inaugural documentation of Diaporthe eres infection and its pathological consequences in wild roses within the Chinese context, providing critical insights into the pathogen’s potential impact on native vegetation and shaping prospective strategies for disease management.

Phosphite (HPO₃^2–) is an effective chemical treatment used to manage Phytophthora diseases in natural and horticultural environments. In New Zealand it is applied as a trunk injection to protect the threatened endemic foundation tree, Agathis australis (kauri), from the invasive pathogen P. agathidicida. It is applied as a foliar spray in natural ecosystems in Australia to protect against a range of Phytophthora-associated diseases and retain plant biodiversity and abundance. Foliar spray application could be a useful method for broad area treatment and to protect isolated and difficult-to-reach stands of kauri, or in plant production settings. In this study, we assessed the efficacy of phosphite when applied as a foliar spray to inhibit P. agathidicida colonisation, the phytotoxicity response and whether the phosphite was translocated to the roots using two glasshouse experiments with 2- and 6-year-old kauri plants. The foliar phosphite treatment effectively reduced colonisation by P. agathidicida in the 2-year-old plants and elevated concentrations of phosphite in the roots of the 6-year-old plants were detected. Phytotoxicity increased with increasing phosphite concentration in both trials. The addition of the surfactant Du-Wett® reduced phytotoxicity for older leaves in the 6-year-old plants. In both assays, phytotoxicity symptoms were most severe on young leaves but had no effect on the production of fresh growth following treatment, suggesting that any ill effects were short-lived. This study indicates that phosphite foliar sprays may be an effective tool to manage kauri dieback under the appropriate circumstances.

Leaf spot disease poses a significant threat to cantaloupe (Cucumis melo L.) production in Vietnam due to its detrimental impact on yield, fruit quality, and economic profitability. Despite its importance, the causal agents and epidemiological patterns of the disease remain poorly understood. This study investigated the prevalence of leaf spot disease in three major cantaloup-growing regions in southern Vietnam, including Binh Duong, Tay Ninh, and Ho Chi Minh City, and further identified the responsible pathogens. Disease monitoring revealed that disease incidence (DI) ranged from 15 to 22% during fruit maturation at 50 days after planting. Additionally, the disease severity index (DSI) varied from 6.33 to 11.89, highlighting the necessity of pathogen identification to develop effective disease management strategies. Through morphological characterization, molecular analysis of ITS, tub, and TEF1α gene regions, and pathogenicity tests following Koch’s postulates, two fungal pathogens were identified: Nigrospora sphaerica (N1) and Curvularia lunata (N2). Pathogenicity studies confirmed their high virulence, with both pathogens causing significant disease symptoms by 11 days post-inoculation, consistent with Koch’s postulates. This study represents the first report of these pathogens causing leaf spot disease in cantaloupe in Vietnam, providing crucial insights for developing effective disease management strategies in the region.

Resistance-inducing compounds represent a novel strategy for managing plant diseases. This study investigated the efficacy of benzothiadiazole (BTH) in mitigating cucumber damping-off disease through seed pretreatment under greenhouse conditions. The expression patterns of defense genes (PR1, PAL1, and LOX) were assessed at multiple time points (0, 24, 48, and 72 h) post-pathogen inoculation via qPCR. Disease index analysis revealed a significant reduction in disease severity in the 100 μg/ml BTH treatment group (43.33% disease index) compared with the untreated control group (100% disease index). Following BTH treatment, rapid and robust upregulation of the LOX and PAL1 genes was observed shortly after inoculation, peaking at 72 h and significantly differing from the control levels. Elevated LOX expression indicated that BTH-induced resistance was mediated through the JA signaling pathway. Conversely, PR1 gene expression did not differ significantly between BTH-treated and control plants. These findings underscore BTH as a promising, straightforward, and environmentally safe approach for managing cucumber damping-off disease. This study contributes insights into plant defense mechanisms and highlights BTH’s potential for use in sustainable agricultural practices aimed at enhancing crop protection and productivity.

In March 2024, onion fields at ICAR-DOGR Pune, India, displayed basal rot symptoms averaging 10–15% disease incidence. The pathogen Fusarium equiseti was isolated, identified, and confirmed through sequencing Tef1-α gene primers. Pathogenicity was tested fulfilling Koch’s postulates and the pathogen was re-isolated. To the best of our knowledge, this represents the initial documented occurrence of F. equiseti causing basal rot of onion bulbs in India, emphasizing the necessity of developing management strategies for this pathogen.

Salvia japonica essential oil (SJEO) is a natural active substance that has been widely used in medicine and food preservation. However, the antifungal mechanism of SJEO against plant pathogens is not well understood. This study examined the antifungal activity of SJEO against Fusarium oxysporum (F. oxysporum). The results demonstrated that SJEO significantly inhibits the mycelial growth and conidial germination of F. oxysporum in a dose-dependent manner. Scanning electron microscopy (SEM) confirmed that SJEO induces mycelial shrinkage, deformation, and rupture. Moreover, SJEO treatment substantially reduced the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), with decreases of 82.49%, 82.82%, and 58.38%, respectively, in the EC₅₀-treated group compared to the control group at 60 h. In contrast, the levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) were significantly elevated. SJEO also increased the permeability of the cell membranes of F. oxysporum, which led to the reduction of the cell contents. Additionally, SJEO at the EC₅₀ concentration significantly decreased the activities of endo-1,4-β-glucanase (EG), polygalacturonase (PG), and pectin lyase (PL) by 18.66%, 40.62%, and 80.19%, respectively, compared to the control group at 60 h. Blight in Pinus sylvestris var. mongolica was significantly reduced following SJEO treatment (p < 0.05). In summary, SJEO disrupts cellular redox balance and intensifies lipid peroxidation in cell membranes, leading to increased membrane permeability and ultimately cell death, and reduces the pathogenicity of F. oxysporum. These findings indicate that SJEO holds promise as a novel fungicide for controlling blight in Pinus sylvestris var. mongolica.

Stalk and bulb decay of garlic (Allium sativum L.) was observed in commercial fields in Jiroft County, Kerman Province, Iran. The causal agent was isolated from symptomatic plants and identified as Rahnella perminowiae based on its morphological and biochemical characteristics and confirmed by specific primers and sequence analysis of 16S rRNA, gyrB and atpD genes. The pathogenicity of the isolates was confirmed twice through inoculation experiments on garlic and onion leaves and bulbs, which resulted in the reproduction of symptoms and re-isolation of R. perminowiae. This is the first report of stalk and bulb decay of garlic caused by R. perminowiae.

During field surveys in 2022-23, phytoplasma diseases were a significant threat to the major flower crops of Andhra Pradesh, India, causing substantial economic losses. In this study, symptoms of phytoplasma were observed in three predominant flower crops of Andhra Pradesh: marigold, crossandra, and jasmine. Samples were collected from major flower growing areas of the state and subjected to PCR assays using universal P1/P7, R16F2n/R2 primers for amplification of the 16 S rRNA gene and gene-specific SecAfor2/Rev3 primers for amplification of a part of the secA gene. The 16 S rRNA gene sequence identity percentage based on Blast and in silico RFLP analysis of PCR-amplified phytoplasma 16 S rDNA was used to identify and classify them into sub-groups. The restriction profiles generated by digestion with 17 restriction endonucleases, showed that phytoplasma strains infecting marigold were highly uniform with members of ‘Candidatus Phytoplasma asteris’ (16SrI-B) and the phytoplasma strains infecting crossandra and jasmine were uniform with members of ‘Candidatus Phytoplasma australasiaticum’ (16SrII-D) subgroup. These phytoplasma strains were not previously reported to infect any flower crops in the state. Marigold, crossandra and jasmine are therefore considered new hosts for the 16SrI and 16SrII group phytoplasmas in Andhra Pradesh. In addition, this study also identified some new disease symptoms in marigold plants in addition to previously known ones.

Typical anthracnose symptoms were observed on leaves and fruit of achachairu (Garcinia humilis) in a producing region in Pernambuco, Brazil. The fungi were isolated from necrotic lesions on leaves and fruit to identify the causal agent and subjected to morphological and phylogenetic characterization. Based on these analyses, the species C. theobromicola and C. siamense were identified. The pathogenicity test confirmed that these two species are the causal agents of anthracnose on G. humilis. This is the first report of C. siamense and C. theobromicola causing anthracnose on leaves and fruits of G. humilis worldwide. Here, we also report these two species as pathogens on the fruit of G. brasiliensis (bacupari).