Evaluation of four whole-plant inoculation methods to analyze the pathogenicity of Erwinia amylovora under quarantine conditions

Four methods were tested to assess the fire-blight disease response on grafted pear plants. The leaves of the plants were inoculated with Erwinia amylovora suspensions by pricking with clamps, cutting with scissors, local infiltration, and painting a bacterial suspension onto the leaves with a paintbrush. The effects of the inoculation methods were studied in dose-time-response experiments carried out in climate chambers under quarantine conditions. A modified Gompertz model was used to analyze the disease-time relatiobbnships and provided information on the rate of infection progression (rg) and time delay to the start of symptoms (t0). The disease-pathogen-dose relationships were analyzed according to a hyperbolic saturation model in which the median effective dose (ED50) of the pathogen and maximum disease level (ymax) were determined. Localized infiltration into the leaf mesophile resulted in the early (short t0) but slow (low rg) development of infection whereas in leaves pricked with clamps disease symptoms developed late (long t0) but rapidly (high rg). Paintbrush inoculation of the plants resulted in an incubation period of medium length, a moderate rate of infection progression, and low ymax values. In leaves inoculated with scissors, fire-blight symptoms developed early (short t0) and rapidly (high rg), and with the lowest ED50 and the highest ymax

Effects of leaf wetness duration and temperature on infection of Prunus by Xanthomonas arboricola pv. pruni

Xanthomonas arboricola pv. pruni is the causal agent of bacterial spot disease of stone fruits and almond. The bacterium is distributed throughout the major stone-fruit-producing areas of the World and is considered a quarantine organism in the European Union according to the Council Directive 2000/29/EC, and by the European and Mediterranean Plant Protection Organization. The effect of leaf wetness duration and temperature on infection of Prunus by X. arboricola pv. pruni was determined in controlled environment experiments. Potted plants of the peach-almond hybrid GF-677 were inoculated with bacterial suspensions and exposed to combinations of six leaf wetness durations (from 0 to 24 h) and seven fixed temperatures (from 5 to 35°C) during the infection period. Then, plants were transferred to a biosafety greenhouse, removed from bags, and incubated at optimal conditions for disease development. Although leaf wetness was required for infection of Prunus by X. arboricola pv. pruni, temperature had a greater effect than leaf wetness duration on disease severity. The combined effect of wetness duration and temperature on disease severity was quantified using a modification of the Weibull equation proposed by Duthie. The reduced-form of Duthie's model obtained by nonlinear regression analysis fitted well to data (R = 0.87 and R2adj = 0.85), and all parameters were significantly different from 0. The estimated optimal temperature for infection by X. arboricola pv. pruni was 28.9°C. Wetness periods longer than 10 h at temperatures close to 20°C, or 5 h at temperatures between 25 and 35°C were necessary to cause high disease severity. The predictive capacity of the model was evaluated using an additional set of data obtained from new wetness duration-temperature combinations. In 92% of the events the observed severity agreed with the predicted level of infection risk. The risk chart derived from the reduced form of Duthie's model can be used to estimate the potential risk for infection of Prunus by X. arboricola pv. pruni based on observed or forecasted temperature and wetness durationMinisterio de Educación, Ciencia y Deporte (AGL2013-41405-R, FPU13/04123) of Spain (https://www.mecd.gob.es/). University of Girona (SING12/13, MPCUdG2016/085) (www. udg.edu). European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement number 613678 (DROPSA

Basis for a predictive model of Xanthomonas arboricola pv pruni growth and infections in host plants

Xanthomonas arboricola pv. pruni (Xap) is the causal agent of bacterial spot disease of stone fruits and almond. The bacterium is considered a quarantine pathogen in Europe and it has become a new and emerging threat for European crops. As the disease is strongly influenced by the weather, a forecasting model that predicts Xap infections based on climatic conditions could be implemented in stone fruit integrated pest management. The objective of this work was to constrain the basis for the development of a predictive model of Xap growth and infections, determining the effects of pathogen, host and climatic parameters on infection and disease development. A non-pathogenic specialization of Xap and cross-infection among host species was observed, although strains isolated from peach were the most virulent in peach leaves. Xap was able to infect unwounded leaves and it was observed that the presence of wounds on the leave surface did not favour Xap penetration in peach leaves. Otherwise, the water condition of plants played an important role in Xap infections and disease development in peach. The presence of water congestion and leaf wetness 48 h before inoculation favoured Xap infections and the duration of leaf wetness after inoculation was directly correlated to disease severity. Temperature and leaf age had a significant effect on Xap infections. Temperatures above 20°C favoured Xap infections, which were basically produced in young leaves; whereas severity was significantly lower at temperatures below 15°C and in mature leavesSupported by research grants BR 2013/31 from University of Girona and FPU13/04123 from Spain MECD, and the projects AGL2013-41405-R from Spain MINECO and the European Union Seventh Framework (FP7 / 2007-2013) under the agreement n°613678 (DROPSA

Evaluation of a Reduced Copper Spraying Program to Control Bacterial Blight of Walnut

Walnut blight, caused by Xanthomonas arboricola pv. juglandis, is currently controlled in western Europe through a standard schedule of seven applications of sprayed copper from bud break until harvest. A reduced spray schedule, with the last four applications omitted, was compared to the standard program in experimental plots for 3 years. Bacterial population levels in the spring were not significantly different between trees subjected to reduced sprays and those subjected to the standard schedule, but in summer they were higher in the trees that received fewer sprays compared with the standard program. However, disease control on nuts was similar or even better with the reduced spraying program than with the standard program, with the additional economic benefit of four fewer copper applications. After 3 years of using the reduced spray program, the amount of copper accumulated in the soil was significantly lower (about half) than that found in the soil where the standard spray program was implementedWe thank M. Milagros López for help at the beginning of the project and for providing us with a collection of strains of X. arboricola pv. juglandisinfo:eu-repo/semantics/publishedVersio

Interacció Pseudomonas syringae pv. syringae-perera. Factors determinants i activitat de diversos fosfonats en el desenvolupament de la malaltia

Blast of pear caused by Pseudomonas syringae pv. syringae is one of the bacterial disease that limit pear production throughout the world. Symptoms are characterized by blast of buds and blossoms wich causes significant loss of fruit production, and necrotic spots on leaves or fruits. Control of bacterial blast of pear with chemicals is difficult and is based on copper compounds and antibiontics. However, its use is limited by the low efficacy, phytotoxicity to the plant or emerging resistance of the pathogen. The activity of several phosphonates (fosetil-Al, potassium phosphonate, etephon and fosfomycin) for control of P. syringae pv. syringae infection on pear was determined in this work, and laboratory models for studying P. syringae pv. syringae-pear interaction were developedPseudomonas syringae pv. syringae és un bacteri que ha estat descrit com agent causant de diverses malalties en més de 200 especies vegetals. En perera causa la necrosi bacteriana, que afecta la majoria de zones productores de pera del món, provocant un debilitament dels arbres i una disminució de la productivitat. En el treball que es presenta s'ha determinat l’activitat de diversos fosfonats (fosetil-AI, fosfonat potàssic, etefon i fosfomicina) en el control de la infecció per P. syringae pv. syringae en perera. Per això s'han desenvolupat models d'estudi de la interacció P. syringae pv. Syringae-perera i s'han determinat els factors que afecten la interacció. Aquests models de laboratori, com que han permès conèixer aspectes concrets de la interacció hoste-patogen i definir de forma clara el tipus d'interacció, s'han aplicat a l'estudi de l'activitat dels fosfonats en la interacció P. syringae pv. syringae -perera i en el control de la malalti

Effects of Leaf Wetness Duration, Temperature, and Host Phenological Stage on Infection of Walnut by Xanthomonas arboricola pv. juglandis

Bacterial blight, caused by Xanthomonas arboricola pv. juglandis, is a significant disease affecting walnut production worldwide. Outbreaks are most severe in spring, and closely tied to host phenology and weather conditions. Pathogen infections are mainly observed in catkins, female flowers, leaves, and fruits. In this study, the effect of wetness duration and temperature on walnut infections by X. arboricola pv. juglandis was determined through two independent experiments conducted under controlled environmental conditions. The combined effect of both climatic parameters on disease severity was quantified using a third-order polynomial equation. The model obtained by linear regression and backward elimination technique fitted well to the data (R2 = 0.94 and R2adj = 0.93). The predictive capacity of the forecasting model was evaluated on pathogen-inoculated walnut plants exposed to different wetness duration–temperature combinations under Mediterranean field conditions. Observed disease severity in all events aligned with predicted infection risk. Additionally, the relationship between leaf and fruit age and the disease severity was quantified and modelled. A prediction model, which has been referred to as the WalBlight-risk model, is proposed for evaluation as an advisory system for timing bactericide sprays to manage bacterial blight in Mediterranean walnut orchards

Biocontrol of Stemphylium vesicarium and Pleospora allii on Pear by Bacillus subtilis and Trichoderma spp.: Preventative and Curative Effects on Inoculum Production

Trials under controlled and field conditions were conducted to establish the effect of strategies of application of biological control agents (BCAs) in the reduction of Stemphylium vesicarium and Pleospora allii inoculum production on pear leaf debris. Six BCAs based on different strains of Trichoderma spp. (Tr1, Tr2) and Bacillus subtilis (Bs1, Bs2, Bs3 and Bs4) were evaluated. Two strategies were tested in controlled experiments: application before (preventative strategy) or after (curative strategy) pear leaf debris colonization by S. vesicarium, evaluating the growth inhibition and sporulation of S. vesicarium and the pseudothecia production of P. allii. When the BCAs were applied preventatively, the efficacy of treatments based on B. subtilis was higher than those based on Trichoderma spp. in controlling the pathogen colonization, but that of controlling the inoculum production of S. vesicarium and P. allii was similar. However, when the BCAs were applied curatively, Trichoderma based products were more effective. In field trials, Trichoderma spp. Tr1 and B. subtlilis Bs1 produced a consistent 45–50% decrease in the number of S. vesicarium conidia trapped compared to the non-treated control. We conclude that Bacillus subtilis Bs1 and Trichoderma spp. Tr1 and Tr2 can be expected to reduce fungal inoculum during the pear vegetative period by at least 45–50%. Additionally, Trichoderma spp. Tr1 and Tr2 have the potential to reduce the fungal overwintering inoculum by 80% to 90%.</jats:p