SUGAR BEET ROOT ROTS DURING VEGETATION PERIOD IN UKRAINE - Ecological Consequences of Increasing Crop Productivity - page 210

FIGURE 20.9 Rhizoctonia development depending on temperature in Ukraine.

A biological peculiarity of the fungi should be mentioned, which is the highest
radial velocity of growth when compared with other fungi.
One of the most powerful factors forming phytosanitary state of agrocenosis and
defi ning its infection potential is soil.
It should be emphasized that certain groups of micromyces cenosis are selected by
crops through root exudates. Therefore, variety of pathogens, saprophytes, and toxin-
producing microfl ora rely greatly on crops.
In recent years, because of the intensive use of soil in agrocenosis associated with
long-term growing of the same crops, factor of soil supressivity, that is, an ability of
soil to suppress pathogenic microbiota and epiphytoty is decreasing.
The changes in structure of crops have greatly deteriorated phytosanitary state of
soils because crops often grow at the same place for some years in a row. This leads to
worsening of not only soil microbiological activity but also of its fungistatical proper-
ties (Figure 20.10).