Pyrenochaeta lycopersici can be stored for several years in the soil on plant debris thanks to its mycelium and its microsclerotia (measuring 64 x 450 micrometers). Various alternative hosts incoming grown in rotation with melon are able to host and multiply: lettuce, melon, cucumber, watermelon, tomato, eggplant, pepper, bean, spinach, strawberry, safflower , sugar beet .. . It is the same for several weeds ( Datura stramonium ...). Note that this fungus, although it grows very slowly in the soil, can reach the deep layers.

 

It penetrates the root tissues and colonizes the cortex thanks to its mycelium, gradually causing its rotting or suberization.

 

This fungus exceptionally forms on altered roots pycnidia irregularly sized (Figures 1 to 2), producing conidia ellipsoid of 4-6 x 1-1.5 µm with setae . Given the rarity of these pycnidia, one can think that these structures do not contribute much to its dissemination. The potential spread of P. lycopersici are therefore very limited and depend mostly melon culture-related activities. Thus, the dissemination can take place through contaminated plants and / or substrates, tools and tillage machinery. Unlike other fungi, it recolonizes rather soil slowly disinfected soils. It is for this reason that this practice is effective over a relatively long period of time, provided the method or fumigant has been chosen with care.

P. lycopersici is rather known to thrive in cold climatic conditions . There still seem to be at least 2 types of strains : “cold” strains with a thermal optimum located between 15-20 ° C (northern European strains) and “hot” strains, still pathogenic at 26-30 °. vs. The latter are found in particular in several countries of the Mediterranean Basin (Tunisia, Lebanon ). The monoculture of tomatoes and / or the alternating or non-alternating production of sensitive crops such as melon in the same plot increases the rate of inoculum in the soil and favors its extension therein.