Modelling the effects of temperature and wetness on the polycyclic phase of Stemphylium vesicarium,the pathogen causing purple spot on asparagus (Asparagus officinalis L.) |
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| Authors: | Henrik Bohlen‐Janssen Paolo Racca Bernhard Hau Alexandra Wichura |
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| Affiliation: | 1. Chamber of Agriculture Lower Saxony, Plant Protection Service, Hannover, Germany;2. Central Institute for Decision Support Systems in Crop Protection(ZEPP), Bad Kreuznach, Germany;3. Institute of Horticultural Production Systems, Sec. Phytomedicine, Leibniz Universit?t, Hannover, Germany |
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| Abstract: | The polycyclic phase of Stemphylium vesicarium is the key factor for the forecast and integrated control of purple spot on asparagus. The annual dynamics of airborne conidia were determined under field conditions by conidia traps. From 2013 to 2015, conidia became airborne at the earliest at mid‐July, but the number trapped was considerably enhanced only after mid‐August, early September. The cumulative percentage of trapped conidia was best described using a logistic function depending on the daily temperature sum (base 0°C) accumulated only on days with >0.2 mm of rainfall (R2 = .81). The germination of conidia was modelled by a generalized beta‐modified Chapman Richards function, and the germ tube length was modelled by a generalized beta‐power function. Conidia germinated in a wide temperature range, with an optimum at 23.3°C, whereas germ tube length had a narrow nearly optimum temperature range around 28.7°C, which indicates that infection by conidia is more restricted by germ tube growth than by germination. The effect of temperature on the number of lesions produced by two strains on green asparagus spears had the narrowest optimum range (optimum at 21.9°C) of all parts of the polycyclic phase. In plant tissue, the spread of the fungus depends on the mycelium growth. The mycelium growth of the four strains, which was modelled with data from a petri dish experiment, had an optimum temperature at 24.7°C. |
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| Keywords: | asparagus forecast purple spot SIMSTEM
Stemphylium vesicarium
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