Symptoms on air organs

whether or not in contact with the ground

 In tropical and equatorial zones, Oomycetes are likely to cause symptoms on several vegetables throughout their development cycle and on several of their aerial organs, whether high up or in contact with the ground.

• Organs attacked :

• Symptoms :
  • Wet lesions appearing on the leaves, spreading and rapidly evolving into leaf rot ( aerial blight ) (Figures 1 to 3). This on the seedlings but rather on the adult plants. The tissues eventually either become necrotic and dry out if the climatic conditions become drier.
  • Wet, extensive alterations are also visible on the stem and sometimes the petioles of the plants (figures 4 to 6).
  • Rots on fruits following wet lesions (figures 7 to 15), rather circular and slightly concave, having developed rapidly. Discharge may be associated with these symptoms.

These aerial lesions appear following heavy rains generating splashes carrying soil particles on the aerial organs, or directly on the latter when they are in contact with the ground.

• Signs : fluffy white and airy mycelial felt covering more or less the lesions in humid conditions (figures 2, 4, 5, 7, 10, 13, etc.). Sporangia, oospores, chlamydospores can be observed using a light microscope in degraded tissues.

• Confusions possibles : Rhizoctonia solani , Choanephora cucubitacearum ,  Sclerotium rolfsii , etc.

• Affected production areas :