Estimating inoculum production relative to percent leaf area infected and environmental conditions required for stimulating release ofEntomosporium mespiliconidia onAmelanchier alnifolia

Abstract

Amelanchier alnifolia, commonly known as saskatoon, is a fruit-bearing shrub native to the Canadian Prairies. Currently, production is limited by the fungal pathogen Entomosporium mespili. It was found that there is a positive linear relationship between the relative concentration of E. mespili conidia (X) and the percent of saskatoon leaf area that is infected (Y), as represented by the equation Y = 0.0534X. In a field study, initial disease symptoms appeared 5 d after the first precipitation event that occurred 1 d or more after the date of flowering. A splashdispersed-conidia trap was constructed and used to trap conidia within the canopy of a saskatoon plant and, in both years of this study, conidia were first trapped on the 184th day of the year, which coincided with the exponential increase of percent leaf area infected. Conidia were primarily released during the first 2 h of precipitation events. Information on inoculum production and release will eventually be integrated into a dynamic disease-forecasting model for entomosporium leaf and berry spot caused by E. mespili on saskatoon.Key words: entomosporium leaf and berry spot, Entomosporium mespili, inoculum production, percent leaf area infected, conidia release, Amelanchier alnifolia.Résumé : L'Amelanchier alnifolia, connu sous le nom d'amélanchier ou petite poire, est un arbuste fruitier originaire des Prairies canadiennes. Présentement, le champignon pathogène Entomosporium mespili en restreint la production. Une relation linéaire positive a été trouvée entre la concentration relative de conidies d'E. mespili (X) et le pourcentage de la surface foliaire infectée des amélanchiers (Y); cette relation est représentée par l'équation Y = 0,0534X. Lors d'une étude sur le terrain, les premiers symptômes de la maladie sont apparus 5 d après la première précipitation qui a suivi d'au moins 1 d la date de floraison. Un piège à conidies dispersées par éclaboussure a été construit et employé pour capturer les conidies à l'intérieur du feuillage d'amélanchiers et, lors des deux années de cette étude, les conidies ont d'abord été capturées au 184 e jour de l'année, lequel a coïncidé avec un accroissement exponentiel du pourcentage de la surface foliaire infectée. Les conidies étaient principalement relâchées au cours des deux premières heures des précipitations. L'information sur la production et le relâchement d'inoculum sera éventuellement intégrée à un modèle dynamique de prévision de la maladie pour la tache des feuilles et des fruits causée par l'E. mespili sur l'amélanchier.Mots clés : tache des feuilles et des fruits, Entomosporium mespili, production d'inoculum, pourcentage de la surface foliaire infectée, relâchement de conidies, Amelanchier alnifolia.Holtslag et al.: Entomosporium on saskatoon / conidial production / effect of environment and disease levels 378

The development of a dynamic diseaseforecasting model to controlEntomosporium mespilionAmelanchier alnifolia

“…Once the phenological stage of budbreak is reached, the disease-forecasting model awaits the first rain event occurring 1 d or more after the date of flowering, because this coincides with the beginning of the infection period (Holtslag et al 2003b). The date of flowering can be predicted using the phenological model, or observed visually and entered into the disease-forecasting model when more than 50% of the inflorescences in the orchard have reached the flowering stage of development.…”

“…Given that there is a direct relationship between the leaf area that is infected with entomosporium leaf and berry spot and inoculum production (Holtslag et al 2003b), an estimate of orchard inoculum potential can be made using a standardized protocol for disease assessment at the end of the growing season. This assessment has the potential to ensure that an unbiased estimate of the mean leaf area infected is calculated (Jones and Windels 1991).…”

“…1, module A). The regression equation originally developed to estimate E. mespili inoculum production on infected saskatoon leaves (Holtslag et al 2003b) was multiplied by a constant of 0.1 to reduce its value. This modified regression equation represented a measure of inoculum potential and was used to calculate the DPI for the first precipitation event that occurred after the start of the infection period.…”

“…Specific details on how phenological data were obtained and analyzed are provided in Holtslag (2003). Data on the relationship of disease to inoculum production was obtained from Holtslag et al (2003b), and the interaction between leaf-wetness duration and temperature is described in Holtslag et al (2003a).…”

“…Disease severity can increase rapidly during the growing season because of the pathogen's short incubation period and polycyclic nature (Sinclair et al 1987;van der Zwet and Stroo 1985). Disease development is dependent on microclimate (Holtslag et al 2003a), host susceptibility (Holtslag et al 2003a;Ronald et al 2001), and the production and release of inoculum (Holtslag et al 2003b). The necrotic angular lesions that form on leaves may eventually coalesce, causing the entire leaf to become chlorotic and abscise prematurely (Bains 2000).…”