Environmental Factors Influencing the Dispersal of Venturia inaequalis Ascospores in the Orchard Air

Abstract

U. S.

A method to monitor airborne Venturia inaequalis ascospores using volumetric spore traps and quantitative PCR

“…A direct comparison of the two methods in a trial orchard would be necessary to determine how the biosensor compares to qPCR detection limits. In this study, the total number of spores that was found during primary ascospore discharge was comparable to data from a study by Rossi et al (2001), in Northern Italy. Large variation in spore numbers is expected to occur between seasons, due to different environmental conditions leading to spore maturation and discharge (James and Sutton, 1982).…”

“…I8896; SigmaAldrich, St. Louis, MO, US) were used to swab daily spore samples from the VST disc, which were then transferred into 2-ml Eppendorf tubes, and frozen at − 20°C until DNA extraction. The number of ascospores observed per day was corrected for volume of air sampled (4.32 m 3 ) and therefore presents the cumulative average concentration of airborne ascospores m −3 of air, as previously described (Rossi et al 2001).…”

“…An infection risk index was calculated from this weather data by multiplying temperatures above 0°C with rain >0.2 mm/h from green tip until full bloom, to calculate the daily "Scab index" if uninterrupted rain periods occurred or maximum of two dry hours (Schwabe 1980a;Rossi et al, 2001). A threshold of >100 indicated a light, >150 medium and >225 a severe infection risk for the susceptible apple leaves.…”

“…Weather models combined with methods to monitor ascospore maturation and predict potential ascospore dose have been shown to be effective in predicting apple scab infection risk (MacHardy 1996;Gadoury et al 2004). Other studies have used spore traps to detect and quantify airborne V. inaequalis ascospores in Europe and Canada, some in comparison with prediction models (Giosue et al 2000;Rossi et al 2001;Ribbert, 2004Ribbert, , 2005Sholberg et al 2005;Carisse et al 2008). In other aerially dispersed plant pathogenic fungi, the inoculum pressure was used as a determining factor for fungicide application (Carisse et al 2005;Carisse et al 2011).…”

“…The two main construction types of traps available are the vacuum or volumetric spore trap (VST) and the rotating-arm impaction spore sampler (Rotorod; Hirst and Stedman 1961;Zuck and Caruso, 1984;Aylor 1993). The vacuum method has the advantage of collecting spores continuously through a rotating disc or on a roll of tape, therefore allowing the user to compare spores collected with weather data of the same time period (Rossi et al 2001). Previously it has been shown that ascospores were mainly discharged during daytime hours in rain events at a rate of up to 4250 spores h −1 per cubic metre air (MacHardy 1994;Warner and Braun 1992;reviewed in MacHardy 1996).…”