Research Note The potential of aged sporangia from Plasmopara viticola to produce zoospores as a requirement to form new infections was determined. Sporangia were produced on potted grapevines and kept on the vines at 22 °C, 30 % r.h. or 22 °C, 60-80 % r.h., respectively. Under these conditions release of zoospores from sporangia could be observed microscopically until 7 d after outbreak of sporangia if liquid water was available. After suspending sporangia in water a first release of zoospores from fresh sporangia was observed after 30 min, from 3-7 d old sporangia not before 180 min. Sporangia kept under the above mentioned conditions were able to infect leaves for at least 9 d after outbreak.
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Kast et al. (2015) studied this question.