Australasian Plant Pathology最新文献

Phytophthora pathogens are responsible for causing disease in a range of environments, including natural, urban, nurseries and horticultural settings, and can be cryptically spread when present as inoculum in infected soil media. By evaluating the survival of Phytophthora inoculum in soil substrates without plants, their potential to be spread cryptically could be better understood. We tested the ability of Phytophthora multivora to survive in and be dispersed from sterile potting mix, forest soil and sand in the absence of plants when introduced as zoospores. We found that P. multivora zoospores readily encysted and survived in the potting mix for up to 76 days. The encysted zoospores were dispersed from the inoculated potting mix pots by overhead watering for up to 49 days. Zoospore cysts accumulated in the bottom sections of the potting mix pots as they were washed downward with each watering event. In contrast, P. multivora did not survive and persist in the sterile sand and forest soil substrates well. At 28 days-post-inoculation, only 10.1% of the destructively harvested replicates were positive with baiting for both sand and soil, while 100% of the potting mix reps were positive. The results raise concerns about the cryptic dispersal of inoculum during restoration projects especially from potting mix and show that zoospore cysts can contribute to the longer-term survival of Phytophthora inoculum. The potential presence of cryptic Phytophthora inoculum in nursery plants should be considered when sourcing plants for restoration projects to avoid inadvertently spreading soil-borne Phytophthora diseases.

All intracellular pathogens, including plant viruses, rely heavily on host cell organelles and metabolites for successful infection and multiplication. During infection, many viruses trigger changes in the host cellular structure, leading to the development of inclusion bodies that typically harbour viral structural and functional proteins. Identifying these inclusion bodies has become an essential diagnostic feature for specific viral infections. Viral inclusions form in various types, differing in location, size, contents, and potential functions. Viruses use these inclusion bodies to ‘house’ a complex mixture of proteins from both the virus and the host cell, aiding in virus replication, translation, and movement within and between cells. These aggregated structures may also serve to shield viral functional complexes from the host defence machinery responsible for viral degradation. This review provides comprehensive information on the existing and recent advances in the ultrastructural changes caused by plant viruses. These ultrastructural changes include the formation of viral inclusion bodies, modifications to the cell cytoskeleton components, endomembrane systems, and various cell organelles. Consequently, this review highlights the strategies used by viruses to replicate, hijack host cell machinery, and disseminate within plant cells.

This study reports the first occurrence of Schizophyllum commune causing wood rot and dieback in almond trees in Uzbekistan. Severe symptoms, including cankers, twig dieback, and extensive wood decay, were observed in a commercial orchard in Ortacirçik, Tashkent, affecting approximately 35% of the trees. The pathogen was isolated and identified using morphological and molecular techniques targeting ITS and LSU regions of rRNA, with pathogenicity confirmed through Koch’s postulates. This study underscores the need for integrated management strategies, including early detection and mitigation practices, to address the challenges posed by wood-decay pathogens and highlights the importance of further research on the epidemiology and resistance mechanisms of S. commune.

A. brassicae (Berk) Sacc. is an important necrotrophic fungal pathogen causing black leaf spot disease in crucifers. Seed can serve as a potential source of inoculum for the transmission of A. brassicae in mustard; however, silique -to-seed transmission of pathogen, the favoring environmental conditions along with the detection threshold for seed were not characterized empirically. So, the objectives of this study were to (i) determine the effect of environmental variables in disease appearance in field conditions in correlation with impact on yield, for this purpose mustard seeds were sown on different sowing date starting from 1st Oct to 19th Nov. at weekly interval; (ii) evaluate the effect of natural silique infection on silique-to-seed transmission of A. brassicae, for this purpose the seeds collected from naturally infected silique were analysed for pathogen recovery (iii) implications of the survival of A. brassicae in stored seeds at different temperature, for this purpose the collected mustard seeds were stored at varied temperature ranges; (iv) evaluate the detection threshold in stored seeds before next sowing season through PCR. The results indicate that development of Alternaria blight was favored by a mean maximum and minimum temperature between 29.0 and 20.9 °C and 11.3 to 6.9 °C respectively with an average relative humidity of more than 80% leading to earliest appearance of symptom in 98 days after sowing (DAS). A silique to seed transmission of approximately 42.6% was recorded for A. brassicae in the seeds collected from silique lot showing 65% disease severity. The stored seeds were monthly checked for pathogen recovery till six months and pathogen recovery of 19.6% and 13.8% was observed in stored seeds in Sep’24(before sowing) at 10ºC and 20ºC respectively while there was no recovery of pathogen in seeds stored at room temperature in Agar plate method. A specific fragment of ~ 400 bp was amplified by PCR using the specific primers and detection limit of 10gm seed at 30.00% silique infestation level and of 1gm at 65.00% silique infestation level was observed in stored seeds.

Rice production is threatened by various pathogens, including plant-parasitic nematodes like those from the genus Hirschmanniella, which can significantly reduce its yield. This study focuses on the morphological and molecular characterisations of Hirschmanniella mucronata associated with rice cultivation in Red River Delta in Vietnam. Morphological analysis revealed that while the three populations of H. mucronata from different regions exhibited some morphometric differences, their overall morphology was consistent with previous data. Morphometric variations were observed and confirmed by Cluster and MDS (Multidimensional Scaling) analyses, indicating possible regional or environmental influences on their morphology, emphasising the need for integrated approaches for accurate nematode identification. Molecular analyses based on D2–D3 of 28 S region identified three distinct clades within H. mucronata sequences. The Vietnamese sequences showed high identity (99.0–99.7% in 28 S and 99.88–99.97% for 18 S regions) to those from Cambodia. However, in 28 S tree, Chinese sequences (KR780066 and MW424471) displayed significant genetic divergence from all other sequences of H. mucronata, suggesting potential cryptic speciation or misidentification. The genetic diversity observed within H. mucronata underscores the complexity of its taxonomy and highlights the importance of using comprehensive identification methods. Additionally, our analysis showed that 18 S sequences of H. mucronata from Vietnam are 100% identical to each other and highly identical to those of H. mucronata available in GenBank (KP179330 and KP179332), differing by only 1–2 bp (99.88–99.97% identity). This study provides robust evidence for the presence of H. mucronata in Vietnam and calls for a reconsideration of previous identifications. This study also provided, for the first time, molecular data and SEM pictures of H. mucronata from Vietnam, facilitating the identification of this species.

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.