RESUMEN
Isoprothiolane (IPT) resistance has emerged in Magnaporthe oryzae, due to the long-term usage of IPT to control rice blast in China, yet the mechanisms of the resistance remain largely unknown. Through IPT adaptation on PDA medium, we obtained a variety of IPT-resistant mutants. Based on their EC50 values to IPT, the resistant mutants were mainly divided into three distinct categories, i.e., low resistance (LR, 6.5 ≤ EC50 < 13.0 µg/mL), moderate resistance 1 (MR-1, 13.0 ≤ EC50 < 25.0 µg/mL), and moderate resistance 2 (MR-2, 25.0 ≤ EC50 < 35.0 µg/mL). Molecular analysis of MoIRR (Magnaporthe oryzae isoprothiolane resistance related) gene demonstrated that it was associated only with the moderate resistance in MR-2 mutants, indicating that other mechanisms were associated with resistance in LR and MR-1 mutants. In this study, we mainly focused on the characterization of low resistance to IPT in M. oryzae. Mycelial growth and conidial germination were significantly reduced, indicating fitness penalties in LR mutants. Based on the differences of whole genome sequences between parental isolate and LR mutants, we identified a conserved MoVelB gene, encoding the velvet family transcription factor, and genetic transformation of wild type isolate verified that MoVelB gene was associated with the low resistance. Based on molecular analysis, we further demonstrated that the velvet family proteins VelB and VeA were indispensable for IPT toxicity and the deformation of the VelB-VeA-LaeA complex played a vital role for the low IPT-resistance in M. oryzae, most likely through the down-regulation of the secondary metabolism-related genes or CYP450 genes to reduce the toxicity of IPT.
Asunto(s)
Ascomicetos , Magnaporthe , Oryza , Magnaporthe/genética , Tiofenos , Oryza/genética , Enfermedades de las PlantasRESUMEN
Biological control agent Bacillus subtilis formulated as Theia is registered for control of fungal and bacterial diseases of fruit crops. Combinations of Theia and strategic concentrations of two demethylation inhibitor (DMI) fungicides were investigated to explore potential synergisms. Bacteria were cultured in nutrient broth and combined with technical grades and two formulations of propiconazole (emulsifiable concentrate [EC] and wettable powder) and metconazole (EC and water-dispersible granule) at 0, 10, 50, 100, and 150 µg/ml of active ingredient. After cocultivation, the optical density (OD600) and colony forming units (CFU/ml) were evaluated. In contrast to EC formulations, the wettable powder or water-dispersible granule formulations at 10 or 50 µg/ml of both DMIs did not affect vegetative cell growth. The mixture of Theia and each formulated DMI at 50 µg/ml of active ingredient resulted in a significant reduction of Monilinia fructicola lesion development on apple, Colletotrichum siamense lesion development on cherry, and Botrytis cinerea lesion development on cherry. The combination of Theia with EC formulations showed weaker disease reduction due to antagonism. Only Theia plus non-EC formulated propiconazole and metconazole significantly reduced brown rot disease incidence of apple compared with the respective solo treatments and anthracnose disease incidence of cherry compared with the untreated control. Our results indicated that at least some DMI fungicides possess bactericidal effects depending on the formulation and concentration. The combination of Theia with a lower-than-label-rate concentration (50 µg/ml) of the DMI fungicides propiconazole and metconazole showed potential for synergistic effects, especially when non-EC formulations were used.
Asunto(s)
Bacillus subtilis , Botrytis , Frutas , Fungicidas Industriales , Enfermedades de las Plantas , Triazoles , Fungicidas Industriales/farmacología , Bacillus subtilis/efectos de los fármacos , Triazoles/farmacología , Enfermedades de las Plantas/microbiología , Enfermedades de las Plantas/prevención & control , Botrytis/efectos de los fármacos , Frutas/microbiología , Productos Agrícolas/microbiología , Colletotrichum/efectos de los fármacos , Colletotrichum/crecimiento & desarrollo , Ascomicetos/efectos de los fármacos , Ascomicetos/fisiología , Ascomicetos/crecimiento & desarrolloRESUMEN
Mixtures of fungicides with different modes of action are commonly used as disease and resistance management tools, but little is known of mixtures of natural and synthetic products. In this study, mixtures of metabolites from the rhizobacterium Pseudomonas chlororaphis strain ASF009 formulated as Howler EVO with below-label rates (50 µg/ml) of conventional sterol demethylation inhibitor (DMI) fungicides were investigated for control of anthracnose of cherry (Prunus avium) caused by Colletotrichum siamense. Howler mixed with metconazole or propiconazole synergistically reduced disease severity through lesion growth. Real-time PCR showed that difenoconazole, flutriafol, metconazole, and propiconazole induced the expression of DMI target genes CsCYP51A and CsCYP51B in C. siamense. The addition of Howler completely suppressed the DMI fungicide-induced expression of both CYP51 genes. We hypothesize that the downregulation of DMI fungicide-induced expression of the DMI target genes may, at least in part, explain the synergism observed in detached fruit assays.
RESUMEN
Brown rot caused by Monilinia fructicola is one of the most important diseases affecting peach production in the southeastern USA. Management often involves the use of demethylation inhibitor (DMI) fungicides, but efficacy can be compromised due to overexpression of the MfCYP51 gene encoding the 14α-demethylase of the ergosterol biosynthesis pathway. This study aimed to investigate the influence of the biorational fungicide Howler EVO containing Pseudomonas chlororaphis ASF009 metabolites, on the expression of MfCYP51 in M. fructicola and associated synergy with a DMI fungicide for control of DMI-resistant strains. Mycelia from two DMI-sensitive and three DMI-resistant M. fructicola isolates were exposed or not to propiconazole (0.3 µg/ml), Howler (78.5 µg/ml), or the combination propiconazole + Howler for 6 h prior to RNA extraction. Real-time PCR indicated that Howler reduced the constitutive expression of MfCYP51 in DMI sensitive and two of three DMI-resistant isolates. Propiconazole-induced expression of the DMI target gene was significantly reduced by Howler and by the mixture of Howler plus propiconazole in all isolates. Detached fruit studies on apple revealed that the combination of Howler plus a reduced label rate of Mentor (50 µg/ml propiconazole) was synergistic against brown rot caused by a DMI-resistant isolate in high and low inoculum spore concentration experiments (synergy values of 40.1 and 4.9, respectively). We hypothesize that the synergistic effects against M. fructicola resistant to DMI fungicides based on MfCYP51 gene overexpression can be attributed to reduced 14α demethylase production due to transcription inhibition, which may necessitate fewer DMI fungicide molecules to arrest fungal growth. The use of Howler /DMI mixtures for brown rot control warrants further investigation because such mixtures could potentially allow for reduced DMI fungicide use rates in the field without compromising yield or increased resistance selection.
RESUMEN
Bacterial spot is one of the most serious diseases of peach caused by the pathogen Xanthomonas arboricola pv. pruni (XAP), leading to early defoliation and unmarketable fruit. The pathogen can overwinter in peach twigs and form spring cankers, which are considered the primary inoculum source for early season leaf and fruitlet infection. The amount of overwintering bacterial inoculum plays a critical role for the bacterial spot development, but no reliable quantification method is available. Thus, we developed a long-amplicon propidium monoazide (PMA)-quantitative PCR (qPCR) assay for specific detection of viable XAP cells. The optimized PMA-qPCR assay used 20 µM of PMAxx for pure bacterial suspensions and 100 µM for peach twig tissues. The Qiagen Plant Pro Kit with an additional lysozyme digestion step was the DNA extraction protocol that yielded the best detection sensitivity with the bacteria-spiked peach twig extracts. The PMA-qPCR assay was tested with different mixtures of viable and heat-killed XAP cells in pure bacterial suspensions and bacteria-spiked peach twig tissues. The results showed that this assay enabled sensitive, specific, and accurate quantification of viable XAP cells as low as 103 CFU/ml with the presence of up to 107 CFU/ml of dead XAP cells, while suppressing the amplification of DNA from dead cells. For mixtures of viable and dead cells, the PMA-qPCR results were linearly correlated with the predicted concentrations of viable XAP (R2 > 0.98). Thus, the PMA-qPCR assay will be a suitable tool for quantifying overwintering XAP population on peach trees.
Asunto(s)
Azidas , Enfermedades de las Plantas , Propidio , Prunus persica , Xanthomonas , Azidas/química , Xanthomonas/genética , Xanthomonas/aislamiento & purificación , Propidio/análogos & derivados , Propidio/química , Enfermedades de las Plantas/microbiología , Prunus persica/microbiología , Reacción en Cadena en Tiempo Real de la Polimerasa/métodos , ADN Bacteriano/genética , Árboles/microbiologíaRESUMEN
Xylella fastidiosa causes bacterial leaf scorch in southern highbush (Vaccinium corymbosum interspecific hybrids) and is also associated with a distinct disease phenotype in rabbiteye blueberry (V. virgatum) cultivars in the southeastern United States. Both X. fastidiosa subsp. fastidiosa and X. fastidiosa subsp. multiplex have been reported to cause problems in southern highbush blueberry, but so far only X. fastidiosa subsp. multiplex has been reported in rabbiteye cultivars in Louisiana. In this study, we report detection of X. fastidiosa in rabbiteye blueberry plants in association with symptoms of foliar reddening and shoot dieback. High throughput sequencing of an X. fastidiosa-positive plant sample and comparative analyses identified the strain in one of these plants as being X. fastidiosa subsp. fastidiosa. We briefly discuss the implications of these findings, which may spur research into blueberry as a potential inoculum source that could enable spread to other susceptible fruit crops in South Carolina.
Asunto(s)
Arándanos Azules (Planta) , Enfermedades de las Plantas , Xylella , Xylella/genética , Xylella/aislamiento & purificación , Xylella/fisiología , Arándanos Azules (Planta)/microbiología , Enfermedades de las Plantas/microbiología , South Carolina , Hojas de la Planta/microbiologíaRESUMEN
Emerging fungal pathogens have always been an issue of concern in southeastern U.S. strawberry production. In 2023, an unusual outbreak of Gnomonia leaf blotch occurred at one North Carolina (NC) and multiple South Carolina (SC) strawberry farms and marked the first report of its occurrence in SC. Molecular identification and phylogenetic analysis of isolates from multiple locations identified the fungus Gnomoniopsis fructicola as the causal agent. In vitro germination of G. fructicola progressed slowly and remained less than 40% even after 24 h of incubation. Similarly, germ tube growth was slow compared to other pathogens. Slow symptom development on strawberry leaves of young strawberry plants grown in the greenhouse started 5 weeks after inoculation. Once the pathogen established on greenhouse plants, leaf necrosis forming blotches was observed. The baseline sensitivity of G. fructicola isolates to commonly used chemical classes of fungicides was assessed. Propiconazole, cyprodinil, pyraclostrobin, and fludioxonil were highly effective in mycelial growth assays with EC50 values < 0.01 µg/ml. Iprodione and thiophanate-methyl were also effective with EC50 values ranging from 0.05 to 1.38 and 2.01 to 23.96 µg/ml, respectively. Fluopyram and fenhexamid were ineffective with EC50 values >100 µg/ml. Based on conversations with the producers, the disease outbreak was linked to transplants from the same nursery source. This study reports for the first time the presence of Gnomonia leaf blotch in South Carolina and provides valuable insights into chemical management options for G. fructicola.
RESUMEN
Sterol demethylation inhibitor (DMI) fungicides continue to be essential components for the control of brown rot of peach caused by Monilinia fructicola in the United States and worldwide. In the southeastern United States, resistance to DMIs had been associated with overexpression of the cytochrome P450 14α-demethylase gene MfCYP51 as well as the genetic element Mona, a 65 bp in length nucleotide sequence located upstream of MfCYP51 in resistant isolates. About 20 years after the first survey, we reevaluated sensitivity of M. fructicola from South Carolina and Georgia to propiconazole and also evaluated isolates from Alabama for the first time. A total of 238 M. fructicola isolates were collected from various commercial and two experimental orchards, and sensitivity to propiconazole was determined based on a discriminatory dose of 0.3 µg/ml. Results indicated 16.2, 89.2, and 72.4% of isolates from Alabama, Georgia, and South Carolina, respectively, were resistant to propiconazole. The detection of resistance in Alabama is the first report for the state. All resistant isolates contained Mona, but it was absent from most sensitive isolates. It was unclear if the resistance frequency had increased in South Carolina and Georgia. However, the resistance levels (as assessed by the isolate frequency in discriminatory dose-based relative growth categories) did not change notably, and no evidence of other resistance genotypes was found. Analysis of the upstream MfCYP51 gene region in the resistant isolate CF010 revealed an insertion sequence described for the first time in this report. Our study suggests that current fungicide spray programs have been effective against increasing resistance levels in populations of M. fructicola and suppressing development of new resistant genotypes of the pathogen.
Asunto(s)
Ascomicetos , Fungicidas Industriales , Triazoles , Estados Unidos , Fungicidas Industriales/farmacología , Ascomicetos/genética , GeorgiaRESUMEN
Conventional fungicides are used in IPM programs to manage fungal plant pathogens, but there are concerns about resistance development in target organisms, environmental contamination, and human health risks. This study explored the potential of calcium propionate (CaP), a common food preservative generally recognized as safe (GRAS) to control fungicide-resistant plant pathogens, mainly Botrytis cinerea, and botrytis blight in ornamentals. In-vitro experiments using mycelium growth inhibition indicated a mean EC50 value for CaP (pH 6.0) of 527 mg/L for six isolates of Botrytis cinerea as well as 618, 1354, and 1310 mg/L for six isolates each of Monilinia fructicola, Alternaria alternata, and Colletotrichum acutatum. In vitro efficacy tests indicated CaP equally inhibited mycelium growth of fungal isolates sensitive and resistant to FRAC codes 1, 2, 3, 7, 9, 11, 12, and 17 fungicides. CaP at 0.1% (pH 6.0-6.5) reduced infection cushion (IC) formation in vitro, botrytis blight on petunia flowers, and botrytis blight of cut flower roses with little to no visible phytotoxicity. Although higher concentrations strongly inhibited infection cushion formation, they did not improve efficacy and exhibited phytotoxicity. We hypothesize that high concentrations may create tissue damage that facilitates direct fungal penetration without the need for infection cushion and subsequent appressoria formation. This study indicates the potential usefulness of CaP for blossom blight disease management in ornamentals if applied at concentrations low enough to avoid phytotoxicity.
Asunto(s)
Fungicidas Industriales , Humanos , Fungicidas Industriales/farmacología , Botrytis , Flores , Enfermedades de las Plantas/prevención & control , Enfermedades de las Plantas/microbiología , Farmacorresistencia FúngicaRESUMEN
Methyl benzimidazole carbamate (MBC) fungicides were once widely used for brown rot (Monilinia fructicola) control of peach (Prunus persica (L.) Batsch) in the southeastern US, but their use was substantially reduced and often eliminated due to widespread resistance. In this study, 233 M. fructicola isolates were collected from major peach production areas in Alabama, Georgia, and South Carolina, and sensitivity to thiophanate-methyl was examined. Isolates were also collected from one organic and two experimental peach orchards. A discriminatory dose of 1 µg/ml was used to distinguish sensitive (S) and moderately sensitive (S-LR) isolates from low resistant phenotypes, while 50 and 500 µg/ml thiophanate-methyl concentrations were used to determine high resistant (HR) phenotypes. Sequence analyses were performed to identify mutations in the ß-tubulin target gene and detached fruit assays were performed to determine the efficacy of a commercial product against isolates representing each phenotype. Results indicated 55.7%, 63.5%, and 75.9% of isolates from Alabama, Georgia, and South Carolina, respectively, were S to thiophanate-methyl; 44.3%, 36.5%, and 21.4% were S-LR; no isolates were LR; and only 3 isolates (1.3%) from South Carolina were HR. No mutations in S or S-LR isolates were found, but HR isolates revealed the E198A mutation, an amino acid change of glutamic acid to alanine conferring high resistance. The high label rate of a commercial product containing thiophanate-methyl controlled brown rot caused by S and S-LR isolates in detached fruit studies but was ineffective against HR isolates. The combinations of thiophanate-methyl with azoxystrobin or isofetamid, when mixed together and applied in an experimental orchard 14 days preharvest, significantly reduced brown rot incidence on pre and postharvest commercially ripe fruit and efficacy was comparable to that of a grower standard fungicide. These results indicate that thiophanate-methyl may again be useful to peach growers in the southeastern US for brown rot and fungicide resistance management.
Asunto(s)
Fungicidas Industriales , Prunus persica , Tiofanato/farmacología , Fungicidas Industriales/farmacología , Sudeste de Estados UnidosRESUMEN
A new Neopestalotiopsis sp. was recently reported causing outbreaks of leaf spot and fruit rot on strawberry in Florida, Georgia, and South Carolina. In contrast to other Pestalotiopsis pathogens, the new species appears more aggressive and destructive on strawberry. Current chemical options for management are disease suppressive at best, and affected growers have been experiencing major yield losses. In this study, we developed a molecular method based on polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) for identification of the new Neopestalotiopsis sp. from strawberry. Isolates of the new Neopestalotiopsis sp. collected in Florida; isolates of N. rosae, N. honoluluana, N. ellipsopora, N. saprophytica, N. samarangensis, and P. rhododendri; and isolates from South Carolina suspected to be the new Neopestalotiopsis sp. were included in this study. This method is based on PCR amplification of a ß-tubulin gene fragment using a previously published set of primers (Bt2a and Bt2b), followed by use of the restriction enzyme BsaWI. The enzyme cuts the PCR product from the new Neopestalotiopsis sp. twice, yielding fragments of 290 base pairs (bp) and 130 and 20 bp in size, whereas fragments from other species are only cut once, yielding fragments of 420 and 20 bp. This method will aid research labs and diagnostic clinics in the accurate and fast identification of the aggressive Neopestalotiopsis sp. variant from strawberry.
Asunto(s)
Fragaria , Xylariales , Fragaria/genética , Polimorfismo de Longitud del Fragmento de Restricción , Xylariales/genética , Reacción en Cadena de la Polimerasa/métodos , FloridaRESUMEN
Gray mold in strawberry is caused by multiple species of Botrytis, including Botrytis cinerea, B. pseudocinerea, B. fragariae, and B. mali. The species B. cinerea and B. fragariae are widespread in production regions of the eastern United States and Germany, and their distinction is important for disease management strategies. Currently, the only way to differentiate these species in field samples is by PCR, which is time consuming, labor intensive, and costly. In this study, a loop-mediated isothermal amplification (LAMP) technique was developed based on species-specific NEP2 gene nucleotide sequences. The designed primer set specifically amplified B. fragariae DNA and no other Botrytis spp. (B. cinerea, B. mali, and B. pseudocinerea) or plant pathogens. The LAMP assay was able to amplify fragments from DNA extracted from infected fruit using a rapid DNA extraction protocol, confirming its ability to detect low amounts of B. fragaria DNA from field-infected fruit. In addition, a blind test was performed to identify B. fragariae in 51 samples collected from strawberry fields in the eastern United States using the LAMP technique. The B. fragariae samples were identified with a reliability of 93.5% (29 of 32), and none of the B. cinerea, B. pseudocinerea, or B. mali samples included in the test were amplified in 10 min. Our results show that the LAMP technique is a specific and reliable method for the detection of B. fragariae from infected fruit tissue and can help to control this important disease in the field.
Asunto(s)
Fragaria , Fungicidas Industriales , Estados Unidos , Botrytis/genética , Fragaria/genética , Reproducibilidad de los Resultados , ADN de Hongos/genéticaRESUMEN
Cytospora plurivora D.P. Lawr., L.A. Holland & Trouillas has been associated with recent premature peach tree decline in South Carolina, but very little is known about the pathogen or chemical control options. Ninety-three C. plurivora isolates were collected in 2016 and 2017 from 1-year-old peach wood and symptomatic scaffold limbs, respectively, from orchards in six towns in South Carolina. Six unique genotypes were identified based on substantial ITS1-5.8S-ITS2 sequence variability and classified G1 to G6. Three of the genotypes (G2, G3, and G6) were isolated in high frequency in multiple locations of both years. In addition to the genotypic variation, multiple phenotypes were observed between and within genotype groups. Species identity was determined using additional gene loci: ACT, TUB, and EF, and isolates were found to belong to C. plurivora for all genotype groups. All tested genotypes were sensitive to thiophanate-methyl (FRAC 1) but exhibited slightly lower sensitivity to propiconazole and difenoconazole (both FRAC 3). Boscalid, fluopyram (both FRAC 7s), azoxystrobin, and pyraclostrobin (both FRAC 11s) were ineffective in vitro at inhibiting mycelial growth of C. plurivora genotypes. Field inoculation of peach and nectarine trees revealed that all genotypes developed twig cankers with differences in virulence. G1 was most virulent, and G6 was least virulent. This study provides a link between the C. plurivora genetic variability and virulence and provides fungicide sensitivity information that could be used to improve disease management practices.
Asunto(s)
Ascomicetos , Fungicidas Industriales , Fungicidas Industriales/farmacología , Enfermedades de las Plantas , Ascomicetos/genética , Variación GenéticaRESUMEN
Glomerella leaf spot (GLS) and bitter rot (BR), caused by Colletotrichum spp., are major diseases on apple in southern Brazil. Among integrated pest management tools for disease management in commercial orchards, fungicides remain an important component. This study aimed to identify Colletotrichum spp. from cultivar Eva in Paraná state orchards; evaluate their in vitro sensitivity to cyprodinil, tebuconazole, iprodione, and fluazinam; and determine the baseline in vitro sensitivity of these isolates to benzovindiflupyr and natamycin. Most isolates belonged to Colletotrichum melonis and C. nymphaeae of the C. acutatum species complex. The two species varied in sensitivity to fluazinam and tebuconazole, but no variability was found for any other fungicide. The lowest 50% effective concentration (EC50) values of Colletotrichum spp. were observed for cyprodinil (mean EC50 < 0.02) and benzovindiflupyr (mean EC50 < 0.05); EC50 values were intermediate for fluazinam (mean EC50 < 0.33) and tebuconazole (mean EC50 < 0.14), and they were highest for natamycin (mean EC50 < 5.56) and iprodione (mean EC50 > 12). Cyprodinil and fluazinam are registered for use in Brazil for apple disease management but not specifically for GLS and BR. Tebuconazole is one of the few products registered for Colletotrichum spp. control in apples. In conclusion, flowers and fruitlets can serve as sources of inoculum for GLS and BR disease; C. acutatum was the predominant species complex in these tissues; cyprodinil and fluazinam applications may suppress GLS and BR; and benzovindiflupyr and natamycin warrant further investigation for GLS and BR disease control of apple due to comparably high in vitro sensitivity.
Asunto(s)
Colletotrichum , Fungicidas Industriales , Malus , Fungicidas Industriales/farmacología , Natamicina , Brasil , Enfermedades de las Plantas/prevención & controlRESUMEN
Colletotrichum species cause diseases on many plants and are among the 'top 10' fungal plant pathogens. Species of the C. gloeosporioides and C. acutatum complexes are particularly important because they infect temperate fruit crops, but their control relies largely on chemical fungicides. In this study, differences in intrinsic fungicide sensitivity were determined in vitro using isolates of the C. gloeosporioides sp. complex (C. fructicola, C. siamense, and C. tropicale) and the C. acutatum sp. complex (C. fioriniae and C. nymphaeae), which had never been exposed to fungicides. Mycelial growth of all isolates was sensitive to the QoI azoxystrobin, the SDHI benzovindiflupyr, and the new DMI fungicide mefentrifluconazole. The isolates of C. nymphaeae were highly sensitive to the phenylpyrrole fungicide fludioxonil. The isolates of C. gloeosporioides sp. complex were sensitive to the bis-guanidine fungicide iminoctadine-albesilate, whereas those of C. acutatum sp. complex were inherently insensitive. These results are valuable when sensitivity of field populations is monitored in resistance management. Although SDHI fungicides are largely not effective against diseases caused by Colletotrichum species, benzovindiflupyr controlled anthracnose disease of various crops such as kidney bean, garland chrysanthemum, and strawberry, caused by C. lindemuthianum, C. chrysanthemi, and C. siamense, respectively, demonstrating this fungicide to be unique among SDHIs and having a broad control spectrum against anthracnose. To help understanding the reason for differential activity of benzovindiflupyr and boscalid, sdhB gene sequences were analyzed but those of C. lindemuthianum, C. chrysanthemi, and C. scovillei revealed no known mutations reported to be responsible for SDHI resistance in other fungi, indicating that other mechanism(s) than target-site modification may be involved in differential sensitivity to benzovindiflupyr and boscalid, found in Colletotrichum species.
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Colletotrichum , Fragaria , Fungicidas Industriales , Fungicidas Industriales/farmacología , Enfermedades de las Plantas/microbiologíaRESUMEN
Bacterial spot of peach, caused by Xanthomonas arboricola pv. pruni, causes yield loss every year in southeastern U.S. peach orchards. Management is mainly driven by season-long applications of copper-based products, site location, and choice of cultivar. Although tolerance to copper has not been reported in X. arboricola pv. pruni in the United States, adaptation of populations from frequent use is a concern. We collected X. arboricola pv. pruni from shoot cankers, leaves, and fruit of cultivar O'Henry over 2 years from three conventional farms and one organic farm in South Carolina, one orchard per farm. The four farms had been using copper extensively for years to control bacterial spot. X. arboricola pv. pruni was isolated from four canker types (bud canker, tip canker, nonconcentric canker, and concentric canker) in early spring (bud break), as well as from leaf and fruit tissues later in the season at the phenological stages of pit hardening and final swell. X. arboricola pv. pruni was most frequently isolated from cankers of the organic farm (24% of the cankers) and most isolates (45%) came from bud cankers. X. arboricola pv. pruni isolates were assessed for sensitivity to copper using minimal glucose yeast agar and nutrient agar amended with 38 µg/ml or 51 µg/ml of Cu2+. Two phenotypes of copper tolerance in X. arboricola pv. pruni were discovered: low copper tolerance (LCT; growth up to 38 µg/ml Cu2+) and high copper tolerance (HCT; growth up to 51 µg/ml Cu2+). A total of 26 (23 LCT and 3 HCT) out of 165 isolates in 2018 and 32 (20 LCT and 12 HCT) out of 133 isolates in 2019 were tolerant to copper. Peach leaves on potted trees were sprayed with copper rates typically applied at the stages of delayed dormancy (high rate; 2,397 µg/ml Cu2+), shuck split (medium rate; 599 µg/ml Cu2+), and during summer cover sprays (low rate; 120 µg/ml Cu2+), and subsequently inoculated with sensitive, LCT, and HCT strains. Results indicated that the low and medium rates of copper reduced bacterial spot incidence caused by the sensitive strain but not by the LCT and HCT strains. This study confirms existence of X. arboricola pv. pruni tolerance to copper in commercial peach orchards in the southeastern United States, and suggests its contribution to bacterial spot development under current management practices.
Asunto(s)
Cobre , Enfermedades de las Plantas , Prunus persica , Xanthomonas , Agar , Cobre/farmacología , Enfermedades de las Plantas/microbiología , Enfermedades de las Plantas/prevención & control , Prunus persica/microbiología , South Carolina , Xanthomonas/efectos de los fármacosRESUMEN
The fungicide fludioxonil is one of the most effective single-site fungicides available for managing flower blight caused by Botrytis cinerea on fruit and ornamental crops. Although low and moderate levels of resistance to fludioxonil have been reported in the pathogen across the United States and Europe, high resistance has been reported only from greenhouses in China. In this study, two B. cinerea isolates with high resistance (half maximal effective concentration >100 µg/ml) to fludioxonil were detected on ornamental calibrachoa flowers grown in a greenhouse. These isolates exhibited stable resistance for >20 generations, produced symptoms on calibrachoa flowers sprayed with label rates of fludioxonil, and displayed in vitro fitness penalties with decreased mycelial growth (P < 0.0001) and sporulation (P < 0.0001) compared with sensitive isolates. Highly resistant isolates were identified as MDR1h, containing the ΔL/V497 deletion in mrr1. However, resistance levels and in vitro fitness parameter characteristics were not consistent with this phenotype. One isolate contained the mutation L267V between HAMP domains 1 and 2 of the Bos-1 gene, and both isolates exhibited high osmotic sensitivity and reduced glycerol accumulation in the presence of fludioxonil, indicating that high resistance of these isolates may be associated with the high-osmolarity glycerol mitogen-activated protein kinase pathway.
Asunto(s)
Botrytis , Fungicidas Industriales , Botrytis/genética , China , Dioxoles , Farmacorresistencia Fúngica/genética , Europa (Continente) , Flores , Fungicidas Industriales/farmacología , Enfermedades de las Plantas , PirrolesRESUMEN
Although Botrytis fragariae was only recently identified as a new Botrytis species that causes strawberry gray mold, its prevalence extends to many states of the eastern United States. Compared with B. cinerea, which is known to be the causal agent of gray mold on many crop plants including strawberry, B. fragariae appears to have specifically adapted to strawberry and exhibits distinct fungicide sensitivity. This is the first presentation of a high-quality genome assembly of B. fragariae with gene annotation based on sequence homology and deep transcriptome data. The genome sequence information from B. fragariae is expected to help reveal genomic features underlying its host specialization and evolution of distinct fungicide resistance and other novel pathogenicity mechanisms.
Asunto(s)
Fragaria , Fungicidas Industriales , Botrytis/genética , Fungicidas Industriales/farmacología , Enfermedades de las Plantas , Estados UnidosRESUMEN
Colletotrichum spp. cause devastating diseases in agricultural crops, including fruit crops. They can differ in host plant and plant organ specificity and even in fungicide sensitivity. In strawberry, members of the C. gloeosporioides species complex (referred to as C. gloeosporioides) primarily cause crown rot and those of the C. acutatum species complex (referred to as C. acutatum) primarily cause fruit rot. Fludioxonil is registered for use (in combination with cyprodinil; Switch 62.5WG in the US) in strawberry against anthracnose disease caused by Colletotrichum spp. In this study we examined the sensitivity of C. gloeosporioides (C. fructicola and C. siamense) and C. acutatum (C. nymphaeae and C. fioriniae) isolates from different hosts and different geographical locations in the US to fludioxonil and examined possible mechanisms of inherent fungicide tolerance. The dose response to fludioxonil of C. gloeosporioides isolates (including 4 isolates of C. theobromicola) revealed about 70% inhibition of mycelial growth at 1 mg/L that was maintained at 10 mg/L and 100 mg/L and lead to minimum inhibitory concentration (MIC) values >100 mg/L. In contrast, mycelial growth of C. acutatum isolates was completely inhibited at 1 mg/L. C. gloeosporioides isolates were also significantly less sensitive to iprodione. An investigation into possible mechanisms of C. gloeosporioides isolates tolerance to fludioxonil and iprodione revealed no evidence of OS-1 gene involvement. Isolates of both species complexes were equally sensitive to salt stress based on mycelial growth inhibition on potato dextrose agar amended with 2%, 4%, and 6% NaCl. In addition, orthologous amino acid alterations in OS-1 previously linked to fludioxonil resistance in Botrytis cinerea were not found in C. gloeosporioides or C. acutatum isolates. This study also showed limited in vitro inhibitory activity of cyprodinil against isolates of both species complexes (MIC values >100 mg/L) and unveils a potential weakness of the fludioxonil+cyprodinil premixture marketed as Switch 62.5WG against C. gloeosporioides species complexes.
Asunto(s)
Colletotrichum , Botrytis , Dioxoles , Enfermedades de las Plantas , PirrolesRESUMEN
In the European Union (EU), regulation of sterol demethylation inhibiting (DMI) fungicides is tightened due to their suspected endocrine disrupting properties. However, the new DMI fungicide mefentrifluconazole was reported to have high fungicidal activity with minimal adverse side effects. In addition, some evidence suggests inconsistent cross resistance between mefentrifluconazole and other azoles. In this study, mefentrifluconazole and other triazoles were examined for activity to select pathogens sensitive or resistant to DMIs using mycelial growth tests on fungicide-treated culture medium or spray trials using cucumber plants. Cross-resistance was confirmed for all of the fungal species tested but activity levels varied. The sensitivity of Monilinia fructicola from peach to mefentrifluconazole was higher compared to other DMIs. In contrast, the inhibitory activity of mefentrifluconazole was equal or slightly inferior compared to difenoconazole, tebuconazole, propiconazole in Colletotrichum spp., Alternaria alternaria sp. complex and Cercospora beticola isolated from peach and sugar beet, respectively. Similar tendencies (i.e. equal or slightly inferior activity and cross-resistance) were observed for cucumber powdery mildew (Podosphaera xanthii) resistant to triflumizole, myclobutanil, and difenoconazole. Despite cross-resistance to other DMIs, mefentrifluconazole is a promising fungicide for fungal disease control on peach and other crops, with a reportedly more favorable toxicity profile.