Tropical Plant Pathology最新文献

Angular leaf spot caused by Pseudocercospora griseola is one of the most common diseases of bean-grown areas in the world. Knowing the genetic structure of the pathogens enables the development of disease control strategies. The purpose of this study was to analyze genetic variability and population structure of 63 Pseudocercospora griseola isolates collected from greenhouses in Black Sea region of Türkiye. Twenty-seven iPBS and thirty-six SCoT primers were assessed to visualize genetic variation among isolates, and four primers from each marker were used for the entire study. The mean percentage of resolving power per primer was 1.10 and 0.73 for iPBS and SCoT markers, respectively. The dendrogram obtained from the combined dataset of both marker systems divided the isolates into two main groups with a genetic similarity of 92%, which is partially associated with the geographical origin of the isolates. The dendrogram of Nei's genetic distances separated the Zonguldak population from all other populations. Karabük and Bartın were grouped, while Ordu and Giresun departed from these populations. STRUCTURE analysis supported with the highest mean value of Ln likelihood (ΔK = 4; LnP(K) = -432.0) the distribution of P. griseola populations based on the Nei’s dendrogram. The mean genetic differentiation (G_ST) among all populations was a high level at 0.429, but there was a low level of gene flow (N_M) at 0.665. AMOVA analysis showed that 58% of genetic variation was between the isolates within populations, and 42% was among populations. iPBS and SCoT markers were tested for the first time to assess intraspecific variation among the isolates of P. griseola. Both methods were easy to use and gave us detailed and consistent information about the genetic diversity of P. griseola. The results from the study proved that these markers are useful and effective tools in analyzing the genetic structure of P. griseola.

Guar (Cyamopsis tetragonoloba) is an annual crop from which guar gum, a valuable biopolymer in industry, is extracted. The crop is affected by Alternaria spp. causing leaf spots. Accurate identification of the causal agent and semi-automated quantification are important in improving disease management. The objective of this study was to identify the causal agent of leaf spot in Guar, as well as to design an indirect tool using images to quantify severity and identify symptomatic plants. Guar plants showing leaf spot symptoms were collected in fields in Guasave, Sinaloa, Mexico, and fungal isolates were obtained from symptomatic leaves. A representative isolate was characterized by morphology, as well as phylogenetic analysis using partial sequences of three genes (tef1-α, gapdh, and rpb2). Subsequently, using photographs of healthy and diseased leaves with different levels of severity, a six-class scale was designed to represent severity using traditional, semiautomated, and automated image analysis methods such as ImageJ, segmentation using the pliman library of R, and fitting of a convolutional neural network model to detect diseased plants, quantify and classify the areas affected by the disease. The fungus Alternaria alternata was associated with the disease and was characterized. Image analysis methods allowed for the semi-automation of severity quantification by reducing the time and cost involved in the evaluation and with greater accuracy and precision with respect to visual methods.

Bacterial diseases significantly impact wheat production worldwide, leading to yield losses ranging from 10 to 40% under diverse climatic conditions. This study aimed to investigate the genomic diversity of bacterial species associated with foliar lesions on wheat in Argentina. Forty foliar lesions from ten plants were collected and a total of forty strains were isolated. Five pathogenic bacterial species were isolated from the lesions, and their genomes were sequenced and assembled. Species identities were confirmed through average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) comparisons with type species. The isolated species were identified as follows: Pantoea ananatis ARGTR 1–1 (98% ANI, 82% dDDH), Curtobacterium flaccumfaciens pv. flaccumfaciens ARGTR 5–2 (98% ANI, 90% dDDH), Xanthomonas translucens pv. undulosa ARGTR 7–1 (100% ANI, 99% dDDH), Clavibacter tessellarius ARGTR 8–1 (98% ANI, 97% dDDH), and Pseudomonas syringae pv. atrofaciens ARGTR 9–1 (99% ANI, 91% dDDH). It was notable that Xanthomonas translucens pv. undulosa ARGTR 7–1 and Clavibacter tessellarius ARGTR 8–1 were isolated from the same plant. This study provides a comprehensive phylogenetic analysis and whole-genome data of these bacterial pathogens, establishing a basis for omics-based approaches to explore genetic diversity and virulence mechanisms. These findings would contribute to the development of strategies aimed at improving wheat health and productivity in the presence of bacterial diseases.

Anthracnose, caused by Colletotrichum spp. is one of the most devastating disease of strawberry. Identification of strawberry resistance to anthracnose has been a priority in strawberry breeding programs. Here, a total of 34 strawberry genotypes were evaluated for resistance to Colletotrichum gloeosporioides using detached leaf assay. Following C. gloeosporioides inoculation, the activities of defense enzymes such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), superoxide anion (•O₂⁻) accumulation, and expression of pathogenesis-related 1 (PR1) and plant defending 1.2 (PDF 1.2) genes were examined. Two genotypes were resistant (R), seven moderately resistant (MR), thirteen susceptible (S), and twelve highly susceptible (HS). Fragaria nilgerrensis Schlech. and F. mandschurica were resistant to C. gloeosporioides, while F. vesca ‘Hawaii 4’ and Fragaria × ananassa cv ‘Miaoxiang No. 3’ were highly sensitive to the pathogen. Furthermore, the leaves of F. nilgerrensis, displayed more •O₂⁻ production and cell death than ‘Miaoxiang No. 3’ following pathogen inoculation. The activities of defense enzymes such as CAT, POD, and SOD in F. nilgerrensis and F. mandschurica were higher than in “Hawaii 4” and ‘Miaoxiang No. 3’. Following inoculation, PR1, PR5, PDF1.2, and coronatine insensitive 1 gene showed high expression levels in F. nilgerrensis, F. mandschurica, ‘Hawaii 4’, and ‘Miaoxiang No. 3’. This work provides insights into the response of different strawberry genotypes to C. gloeosporioides infection in and will help breeders in selecting strawberry germplasm for disease-resistant breeding programs.

Historically, Fusarium wilt of banana (FWB) caused by Fusarium oxysporum f. sp. cubense (Foc) has rendered hectares of banana unusable in Central and South America. In 2019, tropical race 4 (TR4), the most virulent race of Foc, was detected in South America and its spread to the main banana-producing regions is a matter of time. This study investigates the spatio-temporal dynamics of FWB caused by subtropical race 4 (SR4) and its relationship with environmental features, aiming to provide a basis for epidemiologically-based mitigation actions to contain TR4. One banana cv. ‘Maçã’ (AAB) field was established in 2017 in Minas Gerais, Brazil. Bimonthly assessments of incidence were conducted between 2017 to 2020. Weather variables were also recorded. The spatial pattern was studied using quadrat- and distance-based methods. Temporal analyses were based on epidemiological models fitted to disease progress curves. Average values of weather variables were estimated for intervals of 2-, 4-, 6-, and 8-weeks before a given assessment date seeking for any correlation with FWB incidence and absolute disease progress rate. The first foci were detected six months after planting and were randomly distributed across the field The spatial pattern changed to aggregated when FWB incidence increased (maximum of 43%). The FWB progress curve had a sigmoidal-shape and the Gompertz model provided the best description of the temporal dynamic of FWB. Increases in the rate of progress of FWB were correlated with precipitation four weeks before the evaluation. Mitigation actions based on the spatio-temporal epidemiology of SR4 in highly susceptible cultivars might contribute to prevent total crop losses and the expansion of FWB into non-infested regions.

Rotylenchulus reniformis poses a significant threat to cotton crops in the Brazilian Cerrado, particularly when grown consecutively with soybeans. This nematode has not only become a concern for cotton but has also led to considerable damage in soybean crops, emphasizing the need for effective nematode control in both agricultural settings. The aim of this study was to combine genetic control with the application of biological nematicides, as seed treatment, to manage R. reniformis under greenhouse conditions. Two soybean cultivars, TMG 4182 and Fibra, resistant and susceptible, were used and the biological nematicides used included Purpureocillium lilacinum, Trichoderma harzianum + T. asperellum + Bacillus amyloliquefaciens, B. subtilis + B. licheniformis, and B. firmus. Inoculation with 800 R. reniformis occurred in the cotyledonary stage, with evaluations conducted at 72 and 76 days after inoculation for Experiments 1 and 2, respectively. Nematodes were extracted from the soil and roots, calculating the reproduction factor (RF). The combination of biological nematicides with resistant cultivars did not yield substantial benefits in controlling reniform nematodes in soybean but safeguarding resistant cultivars through the application of chemical or biological nematicides is important to mitigate inoculum pressure on resistance genes. In addition, biological nematicides evaluated in this study did not improve soybean plant development and we concluded that managing reniform nematodes in soybean necessitates the integration of diverse control measures to effectively address the challenges posed by this nematode's impact on crops.

The cassava common mosaic virus (CMV) is a pathogen that affects cassava plants. The complete genome sequence of a CsCMV isolate was obtained from cassava plants in São Paulo state, Brazil. Subsequent field surveys across multiple counties revealed a high prevalence of CsCMV, ranging from 67 to 100%. Phylogenetic analysis demonstrated two distinct genetic groups of CsCMV isolates in São Paulo, with the Brazilian isolate closely related to isolates from the United States and China. Considering that cassava is propagated vegetatively, the high incidence of CsCMV highlights the need to establish programs to obtain virus-free propagation materials.

In 2020, the potyvirus passiflora virus Y (PaVY) was reported infecting soybean in Brazil. Considering its recent detection, little is known about the incidence of the virus in soybean-producing regions and if PaVY can be transmitted through seeds. The objectives of this study were to evaluated the reaction of soybean cultivars to PaVY infection (isolate PaVY-Br), assess the occurrence of PaVY in soybean crops in São Paulo state and investigate aspects related to its seed transmission and host range. An average, 40% of the seeds produced by infected plants exhibited symptoms of coat mottling. PaVY was not detected in 1219 seedlings originated from 811 non-mottled and 408 mottled seeds produced by PaVY-Br-infected soybean plants. The potyvirus was detected, by RT-PCR, on 9.8% of mottled and 37.7% of non-mottled seeds. PaVY-Br infected Canavalia ensiformis, Gossypium hirsutum, Nicotiana benthamiana, Phaseolus vulgaris, Raphanus sativus, and Vigna unguiculata, expanding the host range of this isolate. PaVY was not detected in 800 soybean samples collected from fields of this crop in 12 municipalities from São Paulo state during the crop seasons of 2021/2022 and 2022/2023. Overall, the results demonstrated high susceptibility of soybean cultivars mechanically inoculated with PaVY-Br, a low incidence of PaVY in soybean fields in the major producing regions of the state of São Paulo and that transmission of PaVY-BR through soybean seeds is unlikely.

Clubroot of crucifers caused by the soil-borne pathogen Plasmodiophora brassicae is a very destructive disease worldwide. The pathogen survives for many years in soil as resting spores (RS), which are formed in large numbers within the clubbed roots. RS can accumulate in the soil when brassicas are repeatedly grown, leading to increased levels inoculum for subsequent crops. The rapid spread of the pathogen in all cruciferous vegetable production areas in Colombia put the economy of farmers and the availability of these foods in the local market at risk. DNA-based techniques can be useful in determining the presence and concentration of pathogen in soil, making them valuable diagnostic tools for disease management and decision-making. Although the presence and the concentration of P. brassicae spores in soils from cruciferous producing areas in Colombia were determined using qPCR technique in 2017, to our knowledge no other works have addressed the use of diagnosis tools for management of clubroot in the country. No symptoms of clubroot were observed in horticultural areas in the Nariño department according to the mentioned report, despite finding pathogen DNA in the soil samples. However, significant yield losses caused by clubroot have been reported in Nariño since 2020, and many farms are currently growing alternative crops such as potato, carrot, and non-cruciferous crops because of the high P. brassicae pressure. To assess the risk of growing cruciferous crops, this work aims to validate the qPCR technique to detect and quantify P. brassicae in soil samples from the field. We used a model bioassay of pathogenicity test with various concentrations of P. brassicae and with a known susceptible cultivar of broccoli to standardize the methodology. Soil samples from horticultural fields were analyzed to validate the protocol. The bioassay allowed us to determine that a low concentration of 10 spores g⁻¹ is enough to cause disease symptoms in the host and a concentration of 10² spores of P. brassicae is the limit of detection by the qPCR technique. In the presence of the host, the RS concentration of P. brassicae in the soil increased between five and nine times in a single cycle, demonstrating the high rate of propagation of the pathogen. The Nariño department had the highest pathogen concentrations compared to Cundinamarca and Boyacá departments, which was associated to the lack of risk assessments, control measurements and the consecutive growing of susceptible cruciferous crops in infected fields.

Fusarium wilt of banana (FWB) caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc) is a widely distributed disease that generates devastating losses in banana production. Foc belongs to the Fusarium oxysporum species complex (FOSC) which includes several evolutionary lineages. Nine of them are pathogenic to banana such as F. phialophorum, F. grosmichelli, F. duoseptatum and the most aggressive F. odoratissimum tropical race 4 (TR4). No control method has been successfully implemented to manage FWB, then enhancing the potential of management approaches can avoid or delay disease epidemics and reduce disease severity. Here we determined the antifungal effect of different plant-based extracts against Foc in vitro, and whether the combination of cinnamon (Cinnamomum zeylanicum) extract and Bacillus tequilensis EA-CB0015 cyclic lipopeptides had an additive effect against different Foc lineages in vitro and against FWB in banana plants in greenhouse. We found, from 17 plant-based natural extracts, that cinnamon was highly active against Foc strain IB (race 1). Furthermore, cinnamon and cyclic lipopeptides inhibited different strains of various evolutionary lineages of Foc belonging to race 1 and TR4, and their combination increased in 1.4-fold the effect of the single extracts in vitro. Our results showed that soil concentration of F. odoratissimum TR4-II5 decreased by 1000-fold when treated with the combination of 488 mg L⁻¹ cinnamon and 128 mg L⁻¹ lipopeptides in a soil microcosm system after 5 days of incubation, followed by a partial population recovery after 21 days. In greenhouse experiments, the combination reduced external but not internal FWB symptoms, and cinnamon extract had a significant impact on internal plant symptoms. Taken together, the effect of cyclic lipopeptides with cinnamon extract on Foc supports their function towards delaying the effect of disease progression and suggests that the combination enhances the effect of the single extracts.