SCIMAT / SCIENCE PHOTO LIBRARY SCIMAT / SCIENCE PHOTO LIBRARY
Black Knot is a serious disease of plum trees. It is caused by the fungus, Dibotryon morbosum (also known as Apiosporina morbosa), which overwinters in knots on twigs and branches. In the spring, the fungus produces ascospores within tiny fruiting bodies on the surface of the knots. Wind spreads the ascospores for moderate distances. Those which land on green branches may germinate and cause infection if the twigs remain wet for a sufficient length of time. SEM, Microscope magnification 70x, image width: 1800 micrometers, bar: 200 micrometers).
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