ABSTRACT
On-site detection of inoculum of polycyclic plant pathogens could potentially contribute to management of disease outbreaks. A 6-min, in-field competitive immunochromatographic lateral flow device (CLFD) assay was developed for detection of Alternaria brassicae (the cause of dark leaf spot in brassica crops) in air sampled above the crop canopy. Visual recording of the test result by eye provides a detection threshold of approximately 50 dark leaf spot conidia. Assessment using a portable reader improved test sensitivity. In combination with a weather-driven infection model, CLFD assays were evaluated as part of an in-field risk assessment to identify periods when brassica crops were at risk from A. brassicae infection. The weather-driven model overpredicted A. brassicae infection. An automated 7-day multivial cyclone air sampler combined with a daily in-field CLFD assay detected A. brassicae conidia air samples from above the crops. Integration of information from an in-field detection system (CLFD) with weather-driven mathematical models predicting pathogen infection have the potential for use within disease management systems.
ABSTRACT
Mycosphaerella brassicicola causes ringspot on Brussels sprouts, which can result in substantial yield loss in commercial production. Brussels sprout buttons are downgraded if this pathogen occurs on them. In this study, the effect of temperature and wetness duration was investigated on infection of Brussels sprouts using controlled environments (CE). The effect of temperature and wetness duration on inoculum production and ascospore discharge was also investigated. Infection by M. brassicicola was described using a mathematical model and was compared to estimates of ascospore availability obtained via a volumetric air sampler and immunofluorescence (IF). Infection of M. brassicicola was correlated (r = 0.92) with temperature during leaf wetness periods. The relationship between temperature and time to discharge of 5 and 50% of the cumulative total number of ascospores from ringspot lesions was r = 0.99 and 0.98, respectively (P < 0.001). In field experiments, an optimal wind run (the product of the average wind speed and the period over which that average speed was measured) of 250 to 500 km day-1 was required for the dissemination of ringspot inoculum to field bait plants. Quantification of M. brassicicola inoculum in collected field aerosols was possible using a monoclonal antibody in a plate-trapped antigen enzyme-linked immunosorbent assay. Precoating of the air sampler wells with sodium azide prevented trapped spores from germinating. Ringspot inoculum could be detected and quantified in air samples from commercial crops of Brussels sprouts in the United Kingdom. Low levels of ringspot inoculum measured within crops did not lead to disease development.
