Biology, epidemiology

Rhizopus stolonifer often lives in a saprophytic state on zucchini and squash fruits, and in their environment, becoming an opportunistic pathogen when the physiological state of these fruits is modified (presence of wounds, advanced maturity ... ).

• Storage and sources of inoculum

This saprophytic fungus par excellence and very ubiquitous is present on many plant debris on and in the soil, and on various senescent fruits. It causes damage to various plants: several Cucurbitaceae, eggplant, tomato, broad bean, sweet potato, apricot, peach, plum, corn ...

• Penetration, invasion

R. stolonifer is an opportunistic fungus which settles on Cucurbits from senescent floral organs . For example, the wilted corollas, which persist longer than usual in humid periods, constitute nutritive bases allowing them first to settle and then secondly to colonize the fruits and cause them to rot. Stamens and pistils can also be colonized.
It can also penetrate the fruit through a wide variety of injuries: picking stalk wound, sunburn , apical necrosis , coulure , insect bites, various shocks, etc.)

Subsequently, its mycelium grows very extensively, growing in all directions inside the flesh which gradually decomposes thanks to the action of various enzymes.

• Sporulation and dissemination of the fungus

R. stolonifer , which evolves very quickly in the fruits, does not take long to sporulate in the form of an aerial blackish mold (figure 1) formed by numerous sporangiophores at the origin of innumerable black spores in spore vesicles. (figures 2 and 3). These are very present in the air and are dispersed by the wind over long distances, as well as by splashing water and certain insects.

• Conditions favorable to its development

It grows rapidly and sporulates abundantly in the presence of humidity and when temperatures are mild. Its growth is rapid between 15 and 30 ° C and its thermal optimum for development is between 23 and 28 ° C.