THE INFECTIONS POTENTIAL OF PHYTOPHTHORA NICOTIANAE VAR. NICOTIANAE WATERHOUSE.
At planting time, the soil infectious level is lower than that of seedlings: 18.75% and 52.0% respectively.
In time, the infectious potential depends on the form in which the fungus exists in the soil (spores or mycelium); on the other hand it depends on the fact if the soil was sterilised or not before the introduction of the fungus.
The infectious potential of the soil (when the fungus was introduced in to the soil as spores) lasts for about one to two months. As regards the mycelium it survives for two months in nonsterile soil and up to eleven months in sterile soil.
In greenhouse conditions, when tomatoes are grown continually in two cropping cycles per year, the fungus was caught from the soil throughout the year. Differences occuring in the infections potential of the respective soil and the level of attack during the two cropping cycles depending only on different soil temperatures.