Blight Research Articles

Exogenously applied silver nanoparticles (AgNPs) differentially affect bacterial blight disease control in twenty-seven wheat cultivars

The bacterial blight of wheat is an important global disease causing a significant decline in crop yield. Nanotechnology offers a potential solution for managing plant diseases. Therefore, this research aimed to investigate the effectiveness of silver nanoparticles (AgNPs) in controlling bacterial blight in 27 locally grown wheat cultivars. The study examined the impact of AgNPs at three distinct time points: 1, 3, and 5 days after the onset of the disease. Biochemical assay revealed that one day after applying the disease stress, the Inia cultivar had the highest amount of soluble protein (55.60 μg.g−1FW) content in the treatment without AgNPs. The Azadi cultivar, without AgNPs treatment, had the lowest amount of soluble protein content (15.71 μg.g−1FW). The Tabasi cultivar had the highest activity of the superoxide dismutase (SOD) (61.62 mM.g−1FW) with the combination treatment of AgNPs. On the other hand, the Karchia cultivar had the lowest SOD activity (0.6 mM.g−1FW) in the treatment of disease without AgNPs. Furthermore, three days after the application of stress, the Mahdavi cultivar had the highest amount of soluble protein content (54.16 μg.g−1FW) in the treatment of disease without AgNPs. The Niknejad cultivar had the highest activity of the SOD (74.15 mM.g−1FW) with the combined treatment of the disease without AgNPs. The Kavir cultivar had the lowest SOD activity (1.95 mM.g−1FW) and the lowest peroxidase (POX) activity (0.241 mM g−1FW min−1) in the treatment of the disease with AgNPs. Five days after exposure to stress, the Mahooti cultivar had the highest SOD activity (88.12 mM.g−1FW) with the combined treatment of the disease with AgNPs, and the Karchia cultivar had the lowest SOD activity (2.39 mM.g−1FW) in the treatment of the disease with AgNPs. Further, the results indicated that exposure to AgNPs could improve the antioxidant properties of wheat seeds in blight-infected and disease-free conditions in some cultivars.

Efficacy of Bacillus atrophaeus strain RS36 and Priestia megaterium strain RS91 with Partially Reduced Fertilization for Bacterial Leaf Blight Suppression in Rice Seedlings

Efficacy of Bacillus atrophaeus strain RS36 and Priestia megaterium strain RS91 with Partially Reduced Fertilization for Bacterial Leaf Blight Suppression in Rice Seedlings

First Report of Leaf Blight of Osmanthus fragrans Caused by Diaporthe eres in China.

Osmanthus fragrans is an evergreen garden tree species, with high ecological, social, and economic benefits (Lan et al. 2023), which is widely planted in Guizhou Province. From late April to June 2023, a leaf blight disease was observed on O. fragrans in a bauxite mining area in Qingzhen City, with an incidence of ~50%. Symptoms first appeared at the leaf tip or margin, as irregular brown spots, which gradually coalesced into dark brown patches until the leaves withered and fell off. Symptomatic leaves were collected and surface disinfected with 2% NaClO for 30 s, 75% ethanol for 30 s, rinsed 3 times in sterile ddH2O, air-dried and placed on potato dextrose agar (PDA) medium and incubated at 25°C for 7 d. Fungal colonies on PDA of 9 similar obtained isolates were white, with at least one concentric ring. The reverse was light yellow and gradually turned brown. At 12 d, the pycnidia on PDA was gray to black, spherical or conical, with a diameter of 305.15 μm (n=20). The conidial horns oozed out from pycnidia after 25 d of incubation on Pinus massoniana needles. The alpha conidia were unicellular, fusiform, hyaline, had a guttule at each end, and measured 6.24 ± 0.10 μm × 2.48 ± 0.04 μm (n=50). No beta or gamma conidia were observed. The morphological characteristics were likely to Diaporthe spp. (Gomes et al. 2013). DNA of isolates GH02, GH06 and GH08 was extracted. The internal transcribed spacer region (ITS) and partial sequences of translation elongation factor 1-alpha (TEF1-α), calmodulin (CAL), beta-tubulin (TUB2), and histone H3 (HIS) genes were amplified with primers ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R, CAL228F/CAL737R (Carbone and Kohn, 1999), βt2a/βt2b and CYLH3F/H3-1b (Crous et al. 2004; Glass and Donaldson, 1995), respectively. The sequences of ITS, TEF-1α, TUB2, CAL and HIS were deposited in GenBank (GH02: PP813499, PP813844, PP813846, PP813848 and PP813850; GH06: PP813500, PP813845, PP813847, PP813849 and PP813851; GH08: PP507168 and PP529956 to PP529959). BLAST results showed the sequences of GH08 were highly identical to sequences of Phomopsis mahothocarpi (NR147522 [ITS], 527/530), P. mahothocarpi (MW700277 [TEF-1α], 367/372), D. eres (OR885862 [TUB], 513/513), D. celeris (ON221721 [CAL], 484/486), and D. eres (OP968956 [HIS], 477/477). A phylogenetic tree constructed with MEGA X using Neighbor-Joining algorithm (Felsenstein, 1985) indicated the isolate GH02, GH06 and GH08 separated from D. eres CBS 297.77 previously reported from O. aquifolium in Netherlands, as well as D. osmanthi and D. fusicola from O. fragrans in China (Gomes et al. 2013; Long et al. 2019; Si et al. 2021). Based on these results, the three isolates were identified as D. eres (Chaisiri et al., 2021). The isolate GH08 was deposited in the Forest Protection Laboratory, Guizhou University. To confirm pathogenicity, spore suspensions (1×105 spores/mL) of GH08 were sprayed on healthy detached leaves (n=10) and leaves of 3-year-old potted O. fragrans seedlings (n=8). An equal volume of sterile water was sprayed for the control. Then they were placed at 20°C and 70-80% RH. Similar leaf blight symptoms appeared after 5 and 15d on the inoculated leaves and seedlings, respectively. The re-isolated fungus, was identical to D. eres based on morphological and molecular analysis, thus fulfilling Koch's postulates. To our knowledge, this is the first report of D. eres causing leaf blight of O. fragrans in China, supporting a basis for developing effective methods to manage this disease.

First Report of Bacterial Leaf Blight Disease of Rice Caused by Pantoea ananatis in Yunnan Province, China

First Report of Bacterial Leaf Blight Disease of Rice Caused by <i>Pantoea ananatis</i> in Yunnan Province, China

Gray mold disease on bottle gourd caused by Cladosporium tenuissimum in China.

Bottle gourd [Lagenaria siceraria (Mol.) Stand] is a widely cultivated succulent crop species. In December 2022, a serious bottle gourd disease occurred in the protected vegetable planting base of Xingguo County, Ganzhou City, Jiangxi Province, China, with 85% of the 2,100 plants having gray mold disease-like symptoms, including gray spots on the infected fruit. They quickly expanded at suitable temperature and humidity, forming a gray mold layer with inward depressions, which spread to the fruit stem causing watery rot, and the flesh turned black and started to rot. To isolate the pathogen, fruits of the diseased plants were surface-disinfected with 75% ethanol for 30 s, immersed in 0.1% HgCl2 for 1min, rinsed thrice with sterile water, and cultured on a potato-dextrose agar (PDA) medium at 28°C. Mycelia from the diseased tissue were subcultured on fresh PDA medium to obtain pure cultures. After incubation at 25°C for 7 days, olive-green colonies (~2.5mm·d-1) developed. Cultures developed numerous elliptical and limoniform conidia measuring 2.69~9.79 μm to 2.10~5.92 μm (average 5.62×3.12 μm) (n=20). The morphological characteristics of the pathogen resembled those of Cladosporium spp. Fungal genomic DNA was extracted, and the internal transcribed spacer (ITS), partial translation elongation factor-1 alpha (TEF-1α), and actin (ACT) regions were amplified with primers ITS1/4, TEF-728F/986R, and ACT-512F/783R, respectively, and sequenced (Bensch et al. 2012; Jo et al. 2018). Basic Local Alignment Search Tool analysis (BLAST) revealed that the ITS (accession no. OQ186729), ACT (OQ240962), and TEF-1α (OQ240963) sequences of isolate hjt4 shared the highest similarity (99-100%) with those of Cladosporium tenuissimum (accessions no. OM232068, OM256530, OM256526) (Duccio et al. 2015). A phylogenetic tree of the isolate hjt4 and its close relatives within Cladosporium was constructed using the MEGA X neighbor-joining method. The pathogen was identified as C. tenuissimum based on morphological and molecular characteristics. A specimen (JXAU-H2022982) was deposited at the Herbarium of the College of Agronomy, Jiangxi Agricultural University. To confirm its pathogenicity, seven-day-old healthy bottle gourd fruits were disinfected with 75% ethanol, 1 mm-deep wounds were made with sterilized scalpels, and the plants were inoculated with PDA plugs (0.8 cm in diameter) containing actively growing mycelia of isolate hjt4. Plants inoculated with sterile PDA plugs served as controls. Each group contained three fruits, and the experiment was performed in triplicate. All fruits were incubated in a biochemical incubator at 28°C. After 3 days, the fruit surface shrank, and the flesh turned to a black colour and rotten, which rapidly spread to the branches. Control fruits did not develop any symptoms. Reisolated colonies showed the same morphological traits as those of the inoculation isolates, whereas no target colonies were isolated from the control fruits. The pathogen was previously reported to cause leaf blight disease in Coriandrum sativum (Zhou et al. 2022) and sooty spots on Cape gooseberry (Miyake et al. 2022), among others. To our knowledge, this is the first report of gray mold disease caused by C. tenuissimum on bottle gourd in China. The findings provide an important foundation for monitoring and controlling the spread of this disease.

Comparative analysis on natural variants of fire blight resistance protein FB_MR5 indicates distinct effector recognition mechanisms

FB_MR5 is an NLR protein identified from wild apple species Malus × robusta 5 conferring disease resistance to bacterial fire blight. FB_MR5 (hereafter MrMR5) recognizes the cysteine protease effector EaAvrRpt2 secreted from the causal agent of bacterial fire blight, Erwinia amylovora. We previously reported that MrMR5 is activated by the C-terminal cleavage product (ACP3) of Malus domestica RIN4 (MdRIN4) produced by EaAvrRpt2-directed proteolysis. Here, we show that MbMR5 from a wild apple species Malus baccata share 99.4% amino acid sequence identity with MrMR5. Surprisingly, transient expression of MbMR5 in Nicotiana benthamiana showed auto-activity in contrast to MrMR5. Domain swap and mutational analyses revealed that one amino acid polymorphism in the MbMR5 CC domain is critical in enhancing auto-activity. We further demonstrated that MrMR5 carrying seven amino acid polymorphisms present in MbMR5 is not activated by MdRIN4 ACP3 but recognizes AvrRpt2 without MdRIN4 in Nicotiana benthamiana. Our findings indicate that naturally occurring polymorphisms of MR5 natural variants can confer its cell death-inducing activity and the effector recognition mechanism likely due to altered compatibility with RIN4.

Diversity of Calonectria species from leaves and soils in diseased southern China Eucalyptus plantation

Calonectria leaf blight (CLB) is one of the best-known diseases of Eucalyptus spp., particularly in Asia and South America. Recently, typical symptoms of leaf and shoot blight caused by Calonectria spp. Were observed in a Eucalyptus plantation in the YunNan Province of southwestern China. Isolations were made from diseased leaves and top soil collected below the diseased trees to determine the causal agent of the disease and to consider the distribution characteristics of the Calonectria species. This resulted in 417 isolates, of which 228 were from leaves and 189 were from soil. Based on comparisons of DNA sequences for the act (actin), cmdA (calmodulin), his3 (histone H3), rpb2 (the second largest subunit of RNA polymerase), tef1 (translation elongation factor 1-alpha) and tub2 (β-tubulin) gene regions, as well as morphological characteristics, 11 Calonectria species were identified. These included Calonectria aciculata (0.7 %), Ca. colhounii (1.2 %), Ca. eucalypti (10.6 %) and Ca. honghensis (43.2 %) in the Ca. colhounii species complex, and Ca. aconidialis (15.3 %), Ca. asiatica (9.8 %), Ca. hongkongensis (1.0 %), Ca. ilicicola (6.0 %), Ca. kyotensis (0.5 %), and Ca. yunnanensis (11.3 %) in the Ca. kyotensis species complex. In addition, a novel species, accounting for 0.5 % of the isolates, was discovered and is described here as Ca. dianii sp. nov. in the Ca colhounii species complex. Most (99.1 %) of the isolates collected from the leaves resided in the Ca. colhounii species complex and a majority (95.8 %) of those from the soils were in Ca. kyotensis species complex. These results suggest that Calonectria spp. in the Ca. colhounii species complex infecting leaves might be adapted to that niche and that those in the Ca. kyotensis species complex are better adapted to a soil habitat.

First report of two Pantoea species causing bacterial leaf blight on wheat in the United States.

Wheat (Triticum aestivum) is an important crop worldwide, contributing to about one third of the global caloric intake. In June 2021, leaves with bacterial blight symptoms, including yellow and necrotic lesions running parallel to veins, were found in several fields across five counties in eastern Colorado (Weld, Morgan, Sedgwick, Baca, and Kit Carson). Plants exhibiting these symptoms were scattered throughout fields, but symptoms appeared consistent across counties. To determine the causal agent and complete Koch's postulates, a 1 cm2 symptomatic leaf area was excised and macerated in 0.5 mL of sterilized water from four field samples. The lysate was spread on yeast extract dextrose calcium carbonate medium (YDC agar, 1% yeast extract, 2% dextrose, 2% calcium carbonate, 1.5% agar) to isolate bacteria. Single colonies of yellow, mucoid morphology were selected and streaked on new YDC plates. Isolate genomic DNA was extracted (Zymo Research Quick-DNA Fungal/Bacterial Miniprep Kit, #D6005), and ~30 ng of gDNA was used to amplify the 16S rRNA, gyrB, and rpoB genes of all four isolates (Barret et al., 2015; Delétoile et al., 2009; Krawczyk et al., 2020; Ogier et al., 2019). Amplified PCR products were cleaned (Zymo DNA Clean & Concentrator kit, #D4033) and Sanger sequenced, and all sequences have been deposited in NCBI (16S rRNA: OR707336, OR707337, OR707338, OR707339), (gyrB: PP407951, PP407952, PP407953, PP407954), (rpoB: PP407955, PP407956, PP407957, PP407958). A BLAST search against whole genomes identified one isolate from Kit Carson county (CO314) and two isolates from Baca county (CO316 and CO317) as Pantoea agglomerans with 100% identity for the 16S rRNA, gyrB, and rpoB genes, and one isolate from Weld county (CO315) was 100% identical to Pantoea allii for all three genes. To complete Koch's postulates and confirm Pantoea sp. as the causal disease agents, isolates were grown as lawns on DifcoTM Nutrient Agar (NA) medium (48h, 28℃), suspended in 10 mM MgCl2 using a final optical density of 0.1 (~109 colony forming units per milliliter (CFU/mL)), and syringe-infiltrated into the entire leaf area of 10-day-old wheat seedling leaves (var. Hatcher). Treatments of 10mM MgCl2 and a field isolate that does not cause symptoms, identified as Pseudomonas synxantha by 16S rRNA and gyrB sequencing, were negative controls. Inoculated wheat plants were transferred to a growth chamber (22℃, 90% relative humidity). Symptoms developed 14 days post inoculation (dpi), with the most severe appearing 21 dpi. Each of the four Pantoea isolates were re-isolated from symptomatic leaves by grinding them in a Tissue Lyser II (Qiagen) with two metal beads and diluting with 0.4 mL of sterile water. A 20 µL sample of each isolate was plated on NA (24h, 28℃). The colonies appeared phenotypically identical to the original isolates, and Sanger sequencing confirmed the identities of the isolates. To our knowledge, this is the first report of P. agglomerans causing disease in wheat in the United States, and the first report of P. allii as a wheat disease-causing agent. This report is consistent with previous communications showing P. agglomerans causing wheat disease in China (Gao et al., 2023), and P. ananatis in Poland (Krawczyk et al., 2020). The growing numbers of reports of Pantoea spp. as pathogens in recent years suggests increasing novel disease emergence on cereals worldwide.

DPP: A Novel Disease Progression Prediction Method for Ginkgo Leaf Disease Based on Image Sequences

Ginkgo leaf disease poses a grave threat to Ginkgo biloba. The current management of Ginkgo leaf disease lacks precision guidance and intelligent technologies. To provide precision guidance for disease management and to evaluate the effectiveness of the implemented measures, the present study proposes a novel disease progression prediction (DPP) method for Ginkgo leaf blight with a multi-level feature translation architecture and enhanced spatiotemporal attention module (eSTA). The proposed DPP method is capable of capturing key spatiotemporal dependencies of disease symptoms at various feature levels. Experiments demonstrated that the DPP method achieves state-of-the-art prediction performance in disease progression prediction. Compared to the top-performing spatiotemporal predictive learning method (SimVP + TAU), our method significantly reduced the mean absolute error (MAE) by 19.95% and the mean square error (MSE) by 25.35%. Moreover, it achieved a higher structure similarity index measure (SSIM) of 0.970 and superior peak signal-to-noise ratio (PSNR) of 37.746 dB. The proposed method can accurately forecast the progression of Ginkgo leaf blight to a large extent, which is expected to provide valuable insights for precision and intelligent disease management. Additionally, this study presents a novel perspective for the extensive research on plant disease prediction.

Association between molecular markers and resistance to bacterial blight using binary logistic analysis

The most effective strategy for managing wheat bacterial blight caused by Pseudomonas syringae pv. syringae is believed to be the use of resistant cultivars. Researching the correlation between molecular markers and stress resistance can expedite the plant breeding process. The current study aims to evaluate the response of 27 bread wheat cultivars to bacterial blight disease in order to identify resistant and susceptible cultivars and to pinpoint ISSR molecular markers associated with bacterial blight resistance genes. ISSR markers are recommended for assessing a plant's disease resistance. This experiment is focused on identifying ISSR molecular markers linked to bacterial blight resistance. After applying the bacterial solution to the leaves, we performed sampling to determine the infection percentage in the leaves at different intervals (7, 14, and 18 days after spraying). In most cultivars, the average leaf infection percentage decreased 18 days after spraying on young leaves. However, in some cultivars such as Niknegad, Darab2, and Zarin, leaf infection increased in older leaves and reached up to 100% necrosis. In our study, 12 ISSR primers generated a total of 170 bands, with 156 being polymorphic. The primers F10 and F5 showed the highest polymorphism, while the F7 primer exhibited the lowest polymorphism. Cluster analysis grouped these cultivars into four categories. The resistant group included Qods, Omid, and Atrak cultivars, while the semi-resistant and susceptible groups comprised the rest of the cultivars. Through binary logistic analysis, we identified three Super oxide dismutase-related genes that contribute to plant resistance to bacterial blight. These genes were linked to the F3, F5, and F12 primers in regions I (1500 bp), T (1000 bp), and G (850 bp), respectively. We also identified seven susceptibility-associated genes. Atrak, Omid, and Qods cultivars exhibited resistance against bacterial blight, and three genes associated with this resistance were linked to the F3, F5, and F12 primers. These markers can be used for screening or transferring tolerance to other wheat cultivars in breeding programs.

Occurrence of Neopestalotiopsis clavispora Causing Leaf Blight on Acer oblongum in China.

Acer oblongum is native to Southwest China and is also distributed in Nepal and Northern India. It is an excellent garden ornamental tree species, suitable for solitary planting in courtyards and parks. From June to August 2022, severe leaf blight occurred on A. oblongum in Baihe Wetland Park (32°5'42" N, 112°28'13" E) in Nanyang City, China. The foliar disease rate reached 59% (n=100). Early signs were yellow spots on the leaves, mainly on the middle and edge parts. Then, the lesions gradually expanded, became amorphous, and turned yellowish brown, eventually led to necrosis on leaves and branches. Twenty diseased leaves were collected and the junction areas between infected and healthy tissues were cut into 5 x 5 mm2 pieces. The collected plant materials were sterilized in 75% ethanol and 1% NaClO for 30 s and 1 minute, respectively, followed by rinsing in sterile water, and placing on a potato dextrose agar (PDA) plate supplemented with 50 µg ml-1 streptomycin at 25 °C for 3 days. Colony edges were cut and transferred to new PDA plates for purification culture. A total of 18 purified fungal strains were obtained, which showed similar phenotypes in morphological characteristics. All colonies had spread radially with wavy surfaces, and dense cream to white aerial hyphae. After 14 days in culture, black fruiting bodies appeared. Conidia were fusiform to slightly clavate, with five cells and two or three setae, 4.2 to 7.9 μm × 17.5 to 25.4 μm in diameter (n = 100). The apical and basal cells and setae were colorless, three median cells were brown, and the middle cell was dark brown. Morphological characteristics of all 18 strains were consistent with the genus description of Neopestalotiopsis spp. (Maharachchikumbura et al. 2014). Further molecular identification showed that the ITS region sequences of all strains have extremely high homology with Neopestalotiopsis spp. The β-tubulin gene (TUB), and the translation elongation factor 1-alpha gene (TEF1) were amplified for molecular identification (Shu et al. 2020). The sequences of three representative strains (FE-05, 09, 16) from different regions were deposited in GenBank with accession Nos. OQ867279, OQ867288, OQ867289 (ITS), OQ870207, OQ870208, OQ870209 (TUB), and OQ870204, OQ870205, OQ870206 (TEF1). BLASTn analysis of these sequences showed 99 to 100% identity to Neopestalotiopsis clavispora strains (OK655673, MZ648263 for ITS, ON000362, MZ286974 fr TUB, MH423941, MK512481 for TEF1). These morphological features and molecular identification indicated that the pathogen has the same characteristics as N. clavispora. Pathogenicity was tested on ten healthy 3-month-old seedlings using the three representative strains through in vivo experiments. For each strain, the conidial suspension (106 conidia ml-1) in absorbent cotton balls (50 µl of inoculum) were inoculated onto the healthy leaves of two seedlings, while a total of two other plants were served with sterile water as a blank control. The plants were potted in a climate incubator at 28°C and a relative humidity of approximately 90%. Symptoms consistent with natural lesions were observed on the inoculated leaves after 5 days while the control plants remained healthy. The strains of N. clavispora were reisolated from the symptomatic inoculated leaves, fulfilling Koch's postulates. N. clavispora is known to cause disease in a variety of plants in China, such as Dendrobium officinale (Cao et al., 2022), Fragaria ananassa (Shi et al., 2022), and Garcinia mangostana (Qiu et al., 2019). To the best of our knowledge, this is the first report of N. clavispora causing leaf blight on A. oblongum in China. The yellowing and falling off of leaves would seriously affects the garden landscape. It is necessary to further clarify the host range of the pathogen to select appropriate landscape matching plants in future planning.

Management of Bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae through Integrated approach in western undulating zones of Odisha

Management of Bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae through Integrated approach in western undulating zones of Odisha

Characterization and Fungicide Sensitivity of Phaeosphaeriopsis obtusispora That Causes Marginal Leaf Blight in Agave hybrid H.11648.

Sisal is an important tropical cash crop in southern China. Unfortunately, it is threatened by various diseases. In 2022, a new disease tentatively named marginal leaf blight disease (MLBD) was first observed in sisal fields across Guangxi and Guangdong provinces, with an incidence rate ranging from 13% to 30%. In this work, to isolate and identify the pathogens causing MLBD, sisal leaves exhibiting the typical MLBD symptoms were collected, and nine strains were obtained. Pathogenicity tests, morphological observations, and phylogenetic analyses confirmed that two strains, namely 22GX1-3 and 22GD1-4, identified as Phaeosphaeriopsis obtusispora, were the causative pathogens of MLBD. Further investigations into the biological characteristics of P. obtusispora showed that its mycelia exhibited optimal growth on PDA medium, with the most favourable temperature and pH being 25 °C and 7.0, respectively. The mycelia could grow in temperatures ranging from 10 °C to 32 °C but ceased at 35 °C. Lactose and yeast extract powder were also identified as the optimal carbon and nitrogen sources, respectively. Additionally, the effectiveness of various control agents was assessed on a single strain, 22GX1-3. Among the twelve fungicides tested, difenoconazole was proven the most effective, with an EC50 value of 0.5045 µg/mL. To our knowledge, this is the first report for sisal MLBD caused by P. obtusispora. Our results provide crucial pieces of information for the development of effective management strategies to control sisal MLBD caused by P. obtusispora.

First Report of Erwinia aphidicola Causing Bulb Rot of Onion in Chile.

During the 2021-22 and 2022-23 seasons (December to February), onion plants (Allium cepa L.) showing decay, leaf blight, chlorosis and water soak lesions were collected in Central Chile. Five symptomatic plants were sampled from 20 different onion fields. Brown rot of the external scales was observed in bulbs from two fields: one planted with the cv. Campero (20 ha; O'Higgins Region), and another with cv. Marenge (2 ha; Metropolitan Region). The disease incidence in these fields ranged from 2% to 5%. Isolations were carried out from symptomatic leaves and bulbs from these fields on King's B medium, resulting in small white colonies with smooth margin. Three isolates were selected, two from first field (QCJ3A & QCJ2B), and one from second field (EPB1). A preliminary identification based on 16S rRNA sequences was conducted. BLAST analyses of strains QCJ3A, QCJ2B and EPB1 (GenBank Accession No. PP345601 to PP345603) against the NCBI Database resulted in a match with strains (GenBank Accession No. ON255770.1 and ON255825.1) isolated from infected bulbs in Texas, USA identified as Erwinia spp. (Khanal et al. 2023), with 100% coverage and 100% identity (707 bp out of 707). To evaluate the pathogenicity of these three strains, onion bulbs were inoculated (Guajardo et al. 2023). Toothpicks previously immersed in a bacterial suspension at ~ 108 colony forming units (CFU)/mL were pricked at a 4 cm depth into the shoulders of onion bulbs bought from commercial store and incubated at room temperature. Bulbs inoculated with sterile water served as negative control. A known onion bulb rotting bacterial strain of Dickeya sp. was used as a positive control. At the end of the incubation period (20 days), bulbs were opened longitudinally across their inoculation site, showing that the external scales had a brown color. Negative control remained asymptomatic. Strains were re-isolated from damaged tissue and identified as Erwinia sp. This assay was repeated three times with the same results. For further identification, genomic DNA extraction was carried out using the Blood & Cell Culture DNA Kit (Qiagen), and genome sequencing was performed in the Illumina HiSeq 2500 platform. The Whole Genome Shotgun project for strains QCJ3A, QCJ2B and EPB1 have been deposited at DDBJ/ENA/GenBank under the accession JBANEI010000000, JBANEJ010000000 and JBANEK010000000. The average nucleotide identity (ANI) values were 99.6% (EPB1), 98.2% (QCJ2B), and 99.6% (QCJ3A) and DNA-DNA hybridization (dDDH) values were 96.9% (EPB1), 83.7% (QCJ2B), and 97.1% (QCJ3A), when compared with the type strain Erwinia aphidicola JCM 21238 (GenBank accession No. GCF_014773485.1). The three strains were deposited in the Chilean Collection of Microbial Genetic Resources (CChRGM). Erwinia aphidicola has been previously described causing diseases in common bean (Phaseolus vulgaris) and pea (Pisum sativum), in Spain (Santos et al. 2009) and in pepper (Capsicum annuum) in China (Luo et al. 2018). Its close relative E. persicina has been reported causing bulb rot in onion in Korea (Cho et al. 2019) and garlic in Europe (Galvez et al. 2015). To our knowledge, this is the first report of E. aphidicola causing a bulb rot of onion in Chile. Although the distribution and prevalence of this bacterium in Chilean agroecosystems is not known, it can be a potential cause of losses in onions and other crops such as beans, peas, and peppers. Additional studies should be conducted to determine the host range of Chilean Erwinia aphidicola strains.

Novel sources of resistance to bacterial leaf blight in the USDA Brassica rapa collection

Bacterial leaf blight (BLB), caused by Pseudomonas cannabina pv. alisalensis (Pcal), is a devastating disease that has spread worldwide over the past twenty years. Pcal can infect all Brassica crops and leads to yield losses of Brassica leafy greens across the Southeastern US every year. There are no commercial cultivars of turnip greens with resistance to Pcal and no effective bactericides available. We report the first identification of resistant sources in Brassica rapa L. against bacterial leaf blight, caused by Pcal. The USDA accessions of B. rapa (275 accessions) were screened through multiple tests in greenhouse trials. The three commercial cultivars tested exhibited an intermediate response across all tests and re-tests. Three accessions (Ames 7572, PI 649171, and PI 649183) with significant resistance were identified in the B. rapa germplasm collection. The identified accessions are an important source for development of B. rapa cultivars resistant to Pcal and introgression of the resistant loci into B. napus cultivars.

Hybridizing Long Short-Term Memory and Bi-Directional Long Short-Term Memory Models for Efficient Classification: A Study on Xanthomonas axonopodis pv. phaseoli (XaP) in Two Bean Varieties

This study was conducted on Xanthomonas axonopodis pv, which causes significant economic losses in the agricultural sector. Here, we study a common bacterial blight disease caused by the phaseoli (XaP) bacterial pathogen on Üstün42 and Akbulut bean genera. In this study, a total of 4000 images, healthy and diseased, were used for both bean breeds. These images were classified by AlexNet, VGG16, and VGG19 models. Later, reclassification was performed by applying pre-processing to the raw images. According to the results obtained, the accuracy rates of the pre-processed images classified by the VGG19, VGG16 and AlexNet models were determined as 0.9213, 0.9125 and 0.8950, respectively. The models were then hybridized with LSTM and BiLSTM for raw and pre-processed images and new models were created. When the performance of these hybrid models was evaluated, it was found that the models hybridized with LSTM were more successful than the simple models, while the models hybridized with BiLSTM gave better results than the models hybridized with LSTM. In particular, the VGG19+BiLSTM model attracted attention by achieving 94.25% classification accuracy with pre-processed images. This study emphasizes the effectiveness of image processing techniques in agriculture in the field of disease detection and is important as a new dataset in the literature for evaluating the performance of hybridized models.

Salicylic acid application against bacterial blight resistance in Xa21-introgression Thai rice cultivar ‘Phitsanulok 2’

Rice cultivar ‘Phitsanulok 2’ (‘PSL2’) is popularly grown in lower-northern Thailand, because it has good agricultural traits with high-quality and high-yield grains. However, one significant limitation of rice ‘PSL2’ is its susceptibility to bacterial blight (BB) disease caused by bacteria &lt;i&gt;Xanthomonas oryzae&lt;/i&gt; pv. &lt;i&gt;oryzae (Xoo)&lt;/i&gt;, leading to considerable yield losses. Effort approaches have been used to enhance the BB resistance of rice ‘PSL2’ by introducing the resistance gene &lt;i&gt;Xa21&lt;/i&gt; and using salicylic acid (SA). Thus, the objective of this study was to determine the effects of SA application on BB disease reduction in rice cultivars (‘PSL2’, ‘IRBB21’, and backcrossed lines ‘PSL2-&lt;i&gt;Xa21’&lt;/i&gt; in BC&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;6&lt;/sub&gt;) after&lt;i&gt; Xoo&lt;/i&gt;16PK002 inoculation, compared to a mock treatment control. The results showed that the SA-pretreated rice (2mM) exhibited significantly induced upregulation of the &lt;i&gt;Xa21&lt;/i&gt; gene expression before the &lt;i&gt;Xoo&lt;/i&gt;16PK002-infected rice cultivars ‘IRBB21’ and ‘PSL2-&lt;i&gt;Xa21&lt;/i&gt;-BC&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;6&lt;/sub&gt;’. Additionally, the SA-pretreated rice ‘PSL2-&lt;i&gt;Xa21&lt;/i&gt;-BC&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;6&lt;/sub&gt;’ demonstrated significant suppression of &lt;i&gt;Xoo&lt;/i&gt;16PK002 proliferation (from 1.4 to 2.4-fold reduction), compared to the H&lt;sub&gt;2&lt;/sub&gt;O pretreatment. Similarly, the SA-pretreated rice ‘PSL2-&lt;i&gt;Xa21&lt;/i&gt;-BC&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;6&lt;/sub&gt;’ exhibited increased resistance against BB disease, i.e. reduced lesion lengths (10.0-10.9 cm at 14 DAI and 24.6-28.0 cm at 21 DAI), compared to the water pretreatment (16.8-18.0 cm at 14 DAI and 34.9-35.1 cm at 21 DAI). In summary, the application of the SA-pretreatment in the rice introgression lines ‘PSL2-&lt;i&gt;Xa21&lt;/i&gt;-BC&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;6&lt;/sub&gt;’ resulted in improved defense mechanisms against bacteria &lt;i&gt;Xoo&lt;/i&gt;16PK002 through reduced appearance of symptoms and inhibited &lt;i&gt;Xoo&lt;/i&gt; multiplication.

Setosphaeria turcica, the Maize Leaf Blast Pathogen: Current Status and Infection Mechanisms

The fungal pathogen Setosphaeria turcica causes northern corn leaf blight (NCLB) in maize, sorghum, and related grasses. NCLB is a serious fungal foliar disease of cultivated maize that causes devastating yield losses. S. turcica infects maize leaves by means of a specialized cell, the appressorium, but the regulatory mechanisms that underlie appressorium-mediated infection remain largely unknown. Many regulatory pathways and a large number of genes have been described in S. turcica, and many of these genes have been cloned. Characterization of such disease-related genes is important for understanding the biological mechanisms of interaction between pathogen and host and can guide the development of strategies for disease control. There is a significant level of concern regarding the possible dissemination of the S. turcica pathogen to regions where NCLB is not presently prevalent. This scenario is of considerable concern and necessitates immediate research intervention. The present review brings together information on the epidemiology and infection mechanisms of S. turcica.

First report of maize leaf blight disease caused by Pantoea stewartii subsp indologenes in Kerman Province, Iran

In 2020, a newly emerged leaf blight disease on maize crops was observed in the Kerman province of Iran. Further surveys during 2020–2022 revealed that SC704, Hector, and PL711 were the most affected maize cultivars, with 2–10% disease incidence. Yellow-pigmented colonies were isolated from symptomatic plants on nutrient agar, and Koch's postulates were fulfilled. The causative agent was determined to be Pantoea stewartii subsp indologenes based on phenotypic testing, nucleotide sequencing analysis of the 16S rRNA gene, and step-down PCR tests using P. stewartii subspecies-specific primer sets.

Registration of ‘AuSable’ navy bean

Abstract‘AuSable’ (Reg. no. CV‐358, PI 705150) navy bean (Phaseolus vulgaris L.), developed by Michigan State University AgBioResearch was released in 2023 as an early‐mid season, disease‐resistant, upright, short‐vine bean cultivar with excellent dry down. AuSable was developed with the pedigree breeding method to the F4 generation followed by pure line selection for disease, agronomic, and quality traits. In 6 years of field trials, AuSable yielded 3073 kg ha−1, flowered in 46 days, and matured in 95 days on average. Plants averaged 45 cm in height, with a lodging resistance score of 1.7 and seed size of 22 g 100 seed−1. AuSable combines high yield potential with early midseason maturity in a navy bean seed type. AuSable has outyielded ‘Merlin’ by 17% across 6 years and matured 3 days earlier. It exhibits uniform dry down equivalent to ‘Vigilant’ and is well adapted to the intensively managed, narrow row, direct‐harvested production systems where beans are typically grown in Michigan and the Upper Midwest. AuSable possesses resistance to Bean common mosaic virus, is resistant to anthracnose races 7 and 73, has shown moderate tolerance to white mold, and was as tolerant to post emergence damping off caused by Rhizoctonia solani as other navy beans. It is susceptible to common bacterial blight. The seed size of AuSable (22 g 100 seed−1) is most similar to ‘Valiant’ and slightly smaller than ‘Liberty’ (23 g 100 seed−1). Seed of AuSable meets industry standards for packaging and canning quality in the navy bean seed class.