Rhizopus stolonifer*

rot Rhizopus

General

• Very cosmopolitan mushroom reported on practically every continent in the world. It causes soft and liquid rots on different plants and various organs (mainly fruits), especially at harvest time and during storage. These rots show some similarities to those caused by bacteria. It is also responsible for black mold in bread.
• Shows behavior on eggplant fruits quite comparable to that of Botrytis cinerea ; they can even be observed at the same time on the same fruits.
• Extremely polyphagous, capable of developing on a wide variety of hosts: other Solanaceae (tomato, pepper), but also various Cucurbitaceae (watermelon, zucchini, various squash, pumpkin, vegetable sponge, etc.), carrot, pea, sweet potato , etc.
• Observed both in the open field and under shelters.

* Note that other species are also reported on eggplant, such as Rhizopus oryzae , R. nodusus .

• Organs attacked  : mainly fruits on eggplant.
• Symptoms :
  • Possible colonization of senescent floral parts.
  • Wet lesions on fruits (starting from senescent sepals or remnants of floral parts, wounds) rapidly evolving into a wet and soft rot of caramel brown color (figures).
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• Signs  : a blackish aerial hairy mold more or less covers rotten tissue. Fruitings in the form of tiny black pin heads are visible, materializing the mycelium, but also the sporangiophores of the fungus.
• Possible confusion : rots in Choanephora or Botrytis  

Biology

• Conservation : This mucoral, saprophyte 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 many plants: several Cucurbitaceae, eggplant, tomato, broad bean, sweet potato, various fruit trees (apricot, peach, plum, etc.), corn, etc.
• Infection : penetrates fruits mainly at maturity, in particular by:
  • through the stomata, lenticels and microcracks, various injuries such as damage linked to pathogenic insects or fungi, physiological micro-bursts, bird pecks or sun burns.
    Subsequently, its mycelium develops very extensively, growing in all directions inside the flesh which gradually decomposes thanks to the action of various enzymes (pectinases, amylases);
  • sometimes senescent floral organs;
  • contact of a rotten fruit with a healthy fruit.
• Sporulation : it is rapid on rotten organs with production of sporangiophores harboring innumerable black spores in spore vesicles (figures 1 to 4).
• Spread : The spores are dispersed by wind and drafts, rain, and splash from rains and sprinkler irrigation.
• Favorable conditions : It grows quickly and sporulates abundantly in the presence of humidity and when temperatures are mild. Its thermal development optimum is between 23 and 28 ° C.

Protection

• Drain the soil of the plot well to avoid the formation of puddles.
• Orient the rows of planting in the direction of the prevailing winds so that the plant cover is well ventilated.
• Put in place a mulch to prevent the fruits from coming into contact with the soil.
• Manage irrigations as well as possible so that they are regular and never excessive.
• Avoid sprinkling irrigations,  otherwise perform them at the beginning or during the day to allow the plants to dry up quickly.
• Control other diseases and pests because they are the source of wounds and tissue necrosis conducive to the establishment of R. stolonifer .
• Under shelters, it is imperative to reduce the ambient humidity by ventilating them as much as possible.
• Eliminate the during and at the end of cultivation  fruit and other affected organs , do not leave them on the ground.
• Avoid injuring the fruits and harvesting them at advanced maturity.