Alternaria alternata

Alternaria alternata is a fungal pathogen in the family Pleosporaceae that behaves as an opportunistic parasite on a very wide range of hosts, having been recorded on more than 380 plant species. It causes leaf spots, rots and blights on many plant parts and can also trigger upper respiratory problems and asthma in people with weakened immune systems. Several host specific forms of the fungus attack particular crops, including cucurbits, strawberries and tomatoes, where the tomato infecting form produces a toxin called fumonisin B1 that is essential to its ability to cause stem canker. The fungus needs moist, warm conditions to establish itself and spreads through airborne spores released from lesions on already infected leaves, often growing slowly enough that an infection goes undetected until after seedlings have been transplanted. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/