Australasian Plant Pathology最新文献

Root-knot nematodes (RKNs-Meloidogyne spp.) are among the most significant plant-parasitic nematode genera, causing substantial yield losses in vegetable production. Chemical control remains a primary management option due to its rapid effect and ease of application. However, environmental and human health concerns necessitate more strategic use of pesticides, including integration of compounds already registered for other pests or diseases. This study evaluated the nematicidal efficacy of five systemic or translaminar pesticides—abamectin, emamectin benzoate, spirotetramat, spinosad, and fluopyram—currently used for various disease and pest control in tomato production, when applied via foliar and soil routes against Meloidogyne incognita. Soil applications of fluopyram achieved greatest efficacy, reducing gall formation by 98.4% and egg mass production by 99.2% compared to controls. Notably, foliar applications of fluopyram—not previously reported for nematode management—also provided some suppression (33.2% and 36.0% reductions in galls and egg masses, respectively). Spirotetramat demonstrated specific selectivity, permitting gall formation but achieving substantial egg mass suppression via both soil (98.4%) and foliar (23.9%) applications, effectively breaking the reproductive cycle. Soil-applied abamectin and emamectin benzoate showed moderate efficacy (70.6% and 41.5% gall reduction, respectively), while foliar applications and all spinosad treatments were ineffective. These controlled climate chamber findings suggest that fluopyram and spirotetramat, already integrated into tomato production programs for fungal and insect pest management, may provide supplementary nematode control without additional applications. However, given the inherent limitations of this controlled-environment study (e.g., small pots and sterilized soil), field validation is necessary before recommending these strategies in practice.

Sagittaria virus A (SgVA) is reported for the first time in Sagittaria subulata in aquarium stock in New Zealand. The potyvirus monoclonal antibody PTY-1 and RT-PCR with published SgVA primers detected the virus in four of four vegetatively propagated samples from the national supplier. The virus was not detected in water surrounding the plants nor in seven monocotyledonous or two dicotyledonous plant species used in host range studies. SgVA sequences include motifs necessary for aphid transmission and therefore aphid transmission may occur in wetland habitats.

Endofungal and endohyphal bacteria live inside fungal vegetative or reproductive structures, whereas mycelium-associated bacteria may include bacteria attached to or residing within fungal mycelia. These bacteria can protect fungal hosts from mycophagous organisms and influence fungal interactions with plants. In this study, mycelium-associated bacteria (MAB) were recovered from the mycelium of Pythium aphanidermatum, which causes damping-off disease in several vegetable crops, including cucumber, tomato, and cabbage. Four bacterial strains, designated as PyEB1, PyEB2, PyEB3, and PyEB4, were isolated from Py. aphanidermatum mycelium. Based on 16S ribosomal RNA gene sequences, these MAB isolates were assigned to Pseudomonas, with closest GenBank matches to P. yamanorum (PyEB1), P. brenneri (PyEB2), and P. gessardii (PyEB3 and PyEB4). The cell-free culture supernatant of Pseudomonas sp. PyEB1 induced wilting in tomato seedlings under in vitro conditions, while soil inoculation with the bacterium caused visible chlorosis and stunting. Gas chromatography-mass spectrometry analysis tentatively identified Advastab 405, by library matching, as the predominant component in the hexane extract of the culture supernatant of Pseudomonas sp. PyEB1. Live cultures of PyEB1 reduced recoverable metalaxyl in liquid medium by up to 79.7%. To the best of our knowledge, this is the first report of metalaxyl degradation potential by MAB derived from Py. aphanidermatum.

Citrus quick decline (CQD) is an emerging disorder threatening citrus orchards in southern Iran. The disease causes rapid wilting, leaf desiccation, and death of trees within weeks, leading to significant yield losses. Despite extensive surveys, no known pathogen had been consistently associated with this syndrome. Using next-generation sequencing (NGS), a novel betacytorhabdovirus, tentatively named citrus quick decline-associated virus (CQDaV), was identified in citrus trees showing decline symptoms in Kerman Province. The viral genome displayed the canonical betacytorhabdovirus genome organization (3′-N-P-P3-M-G-L-5′). Phylogenetic analysis based on the complete L protein sequence placed the virus within the genus Betacytorhabdovirus, with Glycyrrhiza betacytorhabdovirus 1 as its closest recognized relative. The presence of CQDaV was confirmed by reverse transcription quantitative PCR in some symptomatic trees but was absent in healthy controls. This study reports the molecular characterization of a novel betacytorhabdovirus infecting citrus, which was found to be associated with symptomatic trees showing rapid decline in southern Iran.

Elsinoe perseae, the causal agent of avocado scab disease, is a high-priority biosecurity threat to the Australian avocado industry. Symptom-based diagnosis is unreliable, and morphological identification is hindered by the slow growth of Elsinoe species on artificial media and the absence of a sexual reproductive stage in the field and in axenic culture. Consequently, a rapid and reliable molecular diagnostic tool capable of detecting the pathogen directly from infected fruit or leaf tissue is essential. In this study, we developed a quantitative PCR (qPCR) assay targeting two genomic regions: the internal transcribed spacer 1 (ITS1) region of the rDNA and the RNA polymerase II subunit B (rpb2) gene. The assay can be applied in either singleplex or duplex formats. Both the ITS- and rpb2-targeted assays consistently detected E. perseae DNA from pure cultures. However, detection in infected avocado leaf and fruit tissues was primarily driven by the ITS assay, whereas the rpb2 assay exhibited reduced sensitivity, likely reflecting differences in copy number between multicopy rDNA regions and the single-copy rpb2 gene. No cross-reactivity was observed against other Elsinoe species or common fungal pathogens of avocado. High analytical sensitivity was achieved, with reliable detection of both targets at concentrations of 10³ copies/µL of synthetic gBlocks dsDNA and 0.1 ng/µL of genomic DNA, using a conservative threshold of Ct ≤ 30. Assay performance was unaffected by minor variations in qPCR reagents and instrument platforms. This assay provides a rapid, sensitive, and highly specific diagnostic tool for biosecurity applications, supporting accurate detection, surveillance, and early response to potential incursions of E. perseae.

Among the various pathogens that cause sugar beet root rot, Rhizoctonia solani is one of the most destructive species globally. This pathogen causes damping-off and root rot during field growth and storage, leading to crop yield losses; therefore, the development of environmentally friendly prevention and control strategies targeting this organism is urgently needed. This study aimed to evaluate, through laboratory and greenhouse experiments, the biological control potential of Bacillus subtilis against the sugar beet root rot pathogen R. solani, and to investigate their plant growth-promoting properties. Pathogenicity tests revealed that all tested fungal isolates were capable of infecting sugar beet plants and causing root rot symptoms. Among them, isolate KA 3 showed the highest percentage of damping-off and root rot severity. Therefore, the most aggressive isolate was selected for subsequent antagonistic and greenhouse experiments. This study employed the dual culture method for in vitro screening. The 15 Bacillus strains isolated from the sugar beet rhizosphere exhibited varying levels of antagonistic activity. Among them, B. subtilis strain K 2 had the strongest activity, with a mycelia inhibition rate of 62.51% against R. solani. Under greenhouse conditions, B. subtilis isolate K2 reduced disease severity from 95.5% in the infected control to 22.4%, corresponding to 76.5% disease suppression, while isolate K5 reduced disease severity to 32.3% (66.2% suppression). In addition, treatment with B. subtilis can significantly promote the growth of infected plants, increasing fresh, dry, root, and root dry weight of sugar beet plants. Furthermore, B. subtilis treatment significantly increased total phenolic and flavonoid contents in sugar beet plants. This study proposes that Bacillus subtilis is a promising biocontrol agent and plant growth promoter, which can be incorporated into integrated disease management (IDM) programs for the sustainable prevention and control of sugar beet root rot.

Black rot disease, caused by the seed-borne bacterial pathogen Xanthomonas campestris pv. campestris (Xcc), reduces cabbage yield, featuring V-shaped chlorotic lesions along leaf margins. In December 2024, typical black rot symptoms were observed on cabbage plants in Churamonkathi Union, Jessore District, Bangladesh. Bacteria isolated from symptomatic leaf tissues on King’s medium B base agar were consistent with Xcc based on morphological and biochemical characteristics. Pathogenicity was confirmed by Koch’s postulates, with characteristic symptoms reproduced on healthy cabbage plants 7–14 days after inoculation (DAI). These pathogenic isolates were consolidated as Xcc by Xcc-specific primers (Xcc_53F/R). Subsequently, race determination using race-specific primers revealed that all pathogenic isolates belonged to race 1, as the primer pair Xcc_R2_89.2 F/R produced a 1523 bp amplicon. Partial 16S rRNA gene sequencing of one representative isolate and phylogenetic analysis confirmed its identity as Xcc. This study provides the morpho-molecular confirmation and race detection of Xcc race 1 causing black rot on cabbage in Bangladesh, where the pathogen was previously reported only from mustard seeds without detailed characterization. The findings will facilitate the development of effective disease management strategies for sustainable cabbage production in the country.

Graphical Abstract

Peach powdery mildew caused by Podosphaera pannosa (Wallr.: Fr.) de Bary (syn. Sphaerotheca pannosa) is a major fungal disease in peach orchards of Iran. During the 2023–2024 growing seasons, a commercial orchard planted with the local cultivar ‘Zafarani’, with a history of severe powdery mildew infection, located in the Zayandeh Rood region, was selected to evaluate the integrated effects of green pruning and fungicide applications on disease management. Two fungicide mixtures were tested: pydiflumetofen + difenoconazole (Miravis Duo^® SC, 20%), applied at 0.0002 (2 ml/10 L), and kresoxim-methyl + boscalid (Collis^® SC, 20/10%), applied at 0.0003 (3 ml/10 L), respectively. The experiment was arranged as a randomized complete block design with six treatments and five replicates, including an untreated control, green pruning alone, individual fungicide applications, and combined fungicide and green pruning treatments. Fungicides were applied five weeks after full petal fall, while green pruning in the combined treatments was performed one day prior to fungicide application. The treatments significantly affected disease incidence and severity on both leaves and fruits (P ≤ 0.01). The highest disease incidence was recorded in the untreated control (71.6%), whereas the lowest incidence was observed in Miravis Duo^® combined with green pruning (1.8% on leaves and 0.4% on fruits). Fruit disease severity in the combined treatment (Miravis Duo^® application plus green pruning) was significantly reduced to less than 0.005, compared to approximately 1.7 in the control group. The integrated use of green pruning and Miravis Duo^® demonstrated a statistically supported synergistic effect. The interaction term in the two-way ANOVA (fungicide × green pruning) was significant (p < 0.01), confirming that the combined treatment produced a greater reduction in disease severity than either factor alone. Under field conditions in the Zayandeh Rood region, this combined strategy reduced fruit disease severity to < 0.005, compared with 1.7 in the untreated control, corresponding to an approximately 99% reduction in disease incidence.