Journal of Phytopathology最新文献

Pseudomonads produce a wide array of antimicrobial compounds including 2,4-diacetylphloroglucinol (DAPG), which possess a broad-spectrum antagonistic effect against phytopathogens. Rhizospheric soil samples were collected from the Solanaceous crops for isolation of fluorescent pseudomonads (FPs). Out of the 32 fluorescent bacterial isolates, 21 showed antagonistic activity against Ralstonia solanacearum (NAIMCC-B-01630) with the highest zone of inhibition at 38.33 mm. Among them, 11 bacterial isolates depicted the production of DAPG in Kings' B medium. DAPG production was detected by TLC and quantified through HPLC analysis. Moreover, the bacterial isolate OD13 exhibited higher DAPG production. Further, the presence of the DAPG-encoding phlD gene within the size of 629 bp and 725 bp was also validated through amplification. These bacterial isolates belonged to the genera Pseudomonas as confirmed by morpho-physiological characterization using the VITEK 2 system. The higher DAPG-producing bacterial isolate was identified as Pseudomonas aeruginosa by polyphasic approach with GenBank accession number OQ781265. Thus, the DAPG-producing rhizospheric Pseudomonas strains can be used as biocontrol agents for bacterial wilt. However, field study is highly essential before its successful application.

In April 2023, leaf curl, crinkling symptoms were found on Conyza canadensis plants around tobacco fields located at Yuxi, Yunan province, China. PCR detection with genus-specific primers showed that symptomatic C. canadensis plants was infected by begomovirus. The full-length viral components and satellite molecules from the diseased C. canadensis (YN-2023) were obtained by enrichment of circular DNA with rolling circle amplification, restriction enzyme digestion, cloning, and DNA sequencing. The viral component (2, 750 nt, OR509733) shared the highest nt identity at 92.4% to tobacco leaf curl Yunnan virus isolate YN5741 (TbLCYNV-YN5741 [CN:Yn:Age:16], MN218671). A satellite molecule (1, 339 nt, OR509734) shared the highest nt identity at 86.5% to tobacco curly shoot betasatellite isolate Y115 (TbCSB-Y115 [CN:Yn:03], AJ457822). Another satellite molecule (1, 357 nt, OR509735) shared the highest nt identity at 94.2% to ageratum yellow vein Singapore alphasatellite (AYVSGA-[Singapore:1998], NC003414). Based on the threshold for classification of Begomovirus, Betasatellite, Alphasatellite, YN-2023 was a new strain of TbLCYNV and associated with TbCSB and AYVSGA. To our best knowledge, this is the first report that C. canadensis is a natural host of TbLCYNV.

Potato black dot became an increasingly severe disease in Inner Mongolia, mainly infecting tubers, causing silvery to brown lesions on tuber skin with poorly defined margins and forming black sclerotia later as a sign of skin blemish diseases which significantly affected the yield and fresh market. The C11 and E21 strains isolated from symptomatic tubers of Harqin and Dalate counties were both identified as Colletotrichum coccodes by morphological and molecular identification. Tubers showing silver or brown scurf and black dot on skin were consistent with symptomatic samples collecting from the field in pathogenicity test. This study for pathogenic identification ascertained a tricky disease of potato in Inner Mongolia of China which will lay the foundation for subsequent studies on disease control.

Spilosoma obliqua nucleopolyhedrovirus (SpobNPV) is known as a biocontrol agent against S. obliqua a polyphagous insect. Genome of an isolate designated as SpobMNPV was sequenced and found to have 136,141 bp, 139 putative open reading frames (ORFs) on both sense (48%) and anti-sense (52%) strands and 97.91% nucleotide similarity with Hyphantria cunea nucleopolyhedrovirus (HycuNPV). All the 38 core genes of baculoviruses were identified and validated in the SpobMNPV genome, which differed from SpobNPV–Manipur isolate in several aspects. In SpobMNPV genome, 7 h were found comprised of 2 to 16 repeated units of 67-bp at each site with an imperfect 30-bp palindrome near the centre in both orientations. Comparison of consensus palindrome sequences (hrcons) present in hrs with that of selected alphabaculovirus group I NPVs revealed them to be completely conserved at each side of the hrcons, that is 1-GxTTTxC-7 and 22-TxGxAAAxC-30. Based on phylogenetic analysis of 38 core genes, SpobMNPV was found closest to the HycuNPV in the group I alphabaculovirus. The complete genome of this isolate is being reported for the first time from North India. The information on genome analysis of SpobMNPV will be an addition to the available database on alphabaculoviruses and also accelerate research on SpobNPV as a component of integrated management of S. obliqua in many economically important crops.

Grey leaf spot (GLS), caused by Cercospora spp., has become a very important foliar disease for second-crop corn season, mainly in South America. Therefore, this study aimed to develop and validate a standard area diagram set (SADs) to estimate the severity of GLS and to apply the SADs established in this study to evaluate the efficacy of fungicides for GLS control in field trials. The SADs with nine levels of severity (0.5; 2; 5; 10; 20; 30; 40; 50 and 60%) improved accuracy, precision and reliability. To evaluate the control of GLS in corn, two experiments spraying chemical fungicides were conducted, one in Rio Verde (GO) (experiment A) and another in Chapadão do Sul (MS) (experiment B). Both experiments were conducted in randomized block design, with 10 treatments and four replicates. For the severity assessment, the SADs elaborated in this study was used. From this severity data over time, disease progress curves, area under the disease progress curve (AUDPC), and yield were obtained. Based on the AUDPC and yield values, all treatments differed from the control. The fungicide fluxapyroxad + pyraclostrobin + mefentrifluconazole had the highest value, giving 72.8% control efficacy and the highest yield maintenance of 43.5%. The other treatments had an intermediate control efficacy and yield. The SADs proposed here is a useful tool for improving visual assessments of GLS severity on corn leaves and fungicides can be used for integrated disease management.

Temperature and water potential are critical factors influencing the germination of Sporisorium scitamineum teliospores and subsequent crop infection. This paper reports on the effect of temperature, water potential and incubation time on S. scitamineum teliospore germination. A field trial was conducted to determine the influence of temperature and length of exposure to teliospores on smut incidence. A 200 μL aliquot of teliospore (1.5 × 10⁶ teliospores/mL) was cultured on water agar (WA) amended by potassium chloride (KCl) or sucrose. The plates were incubated across a range of temperatures and incubation times. For the field trial, sugarcane setts were inoculated and incubated at different temperatures and for varying incubation periods. The results demonstrated that germination decreased with declining water potential with either KCl or sucrose. The greatest germination (95.8%) occurred on unamended WA incubated at 30°C for 6 h. Even at the lowest water potential of −45 bars and 30°C, 50% teliospores were still able to germinate. These results indicate that 30°C is the optimum temperature for teliospore germination and that S. scitamineum may still germinate in fairly dry conditions. However, high temperatures (40°C), greatly reduce S. scitamineum germination. These results are consistent with field trial outcomes, which showed that the highest disease incidence (40.4%) occurred when temperature of inoculation was maintained at 30°C. On the other hand, the incidence was significantly reduced to 5.7% at 35°C. The results suggested consistent conditions for teliospore germination and sugarcane bud infection, with a temperature of 30°C being optimal for both.

Tobacco (Nicotiana tabacum L.) is one of the most important crops in southern Brazil, but little is known about the distribution and diversity of plant parasitic nematodes (PPNs). We surveyed the occurrence and diversity of PPNs in 36 tobacco-growing areas in southern Brazil as well as evaluated their relationship with 19 bioclimatic variables. For these purposes, extracted nematodes (from soil and roots) were identified based on morphological and biochemical traits and estimates of incidence and abundance were obtained, which were used to compute diversity indices. Furthermore, the relationship between taxa and diversity and the influence of bioclimatic variables were studied using principal component analysis (PCA) and generalized linear models (GLMs), respectively. We observed diversity across the sampled sites, with values varying from 0.03 to 1.22 and from 0.05 to 0.76 according to the Shannon-Wiener and Pielou's evenness indices, respectively. Seven genera of PPNs (Meloidogyne, Helicotylenchus, Tylenchus, Xiphinema, Pratylenchus, Paratylenchus and Mesocriconema) were identified, highlighting taxa with high incidence and abundance, such as Meloidogyne (100%; 1800 to 41,850 specimens/250 cm³), Helicotylenchus (100%; 50 to 9850 specimens/250 cm³), and Pratylenchus (86.1%; 50 to 1950 specimens/250 cm³). The PCA disclosed the major roles of Meloidogyne, Tylenchus, and Helicotylenchus in the structure of the PPN communities and their interplays. Among root-knot nematodes, Meloidogyne javanica, M. arenaria and M. incognita were the predominant species. Using GLMs, we found that average annual temperature and annual precipitation strongly influenced the abundance of PPNs as well as the diversity indices (p < .01), with negative and/or positive interactions. Collectively, our findings fill gaps in knowledge about the current impact of PPNs and provide insights into future scenarios, including for other host crops.

Diaporthe spp. (including their asexual Phomopsis states) are important plant pathogens found widely in different host plants, such as pathogens, endophytes or saprobes. In this study, a new species of Diaporthe causing fruit rot in kiwifruit, Diaporthe xiuwenensis sp. nov was isolated from kiwifruit with apparent soft rot symptoms during storage in Guizhou Province, China. Identification was made using morphology and comparison of DNA sequence data of the nuclear ribosomal ITS (internal transcribed spacer) + tef1 (translation elongation factor-1α) + tub2 (β-tubulin) + cal (calmodulin) + his (histone H3) gene regions. This study further described a new Diaporthe species and discussed its morphology and phylogenetic relationships with other Diaporthe species. Koch's postulates tests identified the causative agents of kiwifruit soft rot. The results of pathogenicity test showed that Diaporthe xiuwenensis sp. nov was pathogenic to kiwifruit, and the Koch's postulates were completed.

Fusarium crown rot (FCR) poses a significant threat to wheat crops, causing substantial grain loss and mycotoxin contamination. While chemical fungicides have been effective in controlling this disease, the need for environmentally friendly alternatives is paramount due to concerns about human health and fungicide resistance. This study delves into the efficacy of Pseudomonas plecoglossicida (NR_114226) as a plant growth-promoting and biocontrol agent against Fusarium graminearum (ON685926) and Fusarium pseudograminearum (ON687723). Greenhouse experiments demonstrated a significant reduction in disease severity by 66.06% through seed treatment with this rhizobacterial strain in soil already infested with fungal pathogens. Moreover, significant growth enhancement occurred in F. pseudograminearum-infected seedlings treated with P. plecoglossicida (F4 + P57), increasing plant height from 13.8 to 33.1 cm and root length from 9.56 to 19.62 cm, with notable improvements in fresh and dry weights. The study further validated these findings through enzymatic assays and analysis of synthesized secondary metabolites, including chitinase, protease, hydrocyanic acid, indole acetic acid, phosphate solubilization and siderophore production. These results strongly suggest that P. plecoglossicida has the potential to serve as an effective biocontrol agent against soilborne cereal pathogens.

Cacao (Theobroma cacoa L.) is an important tropical fruit tree used in chocolate production. Among the biotic problems interfering with fruit production, phytopathogenic fungi stand out. During a visit to cocoa production areas in the municipality of Medicilândia, Pará, Brazil (Amazon region), we observed cocoa fruits with dark lesions and greyish-white cottony mycelia growth. In order to determine the aetiological agent's identity, we extracted DNA and amplified part of the TEF-1α and RBP2 genes and compared them with sequences in GenBank using the BLASTn tool. Based on molecular results and phylogenetic analysis, the isolates were identified as Calonectria hawksworthii. Inoculations in cacao fruits showed symptoms after 6 days and were similar to those collected in the field, confirming the postulates. This study is the first report of Ca. hawksworthii causing cocoa bean rot worldwide.