Tomatoes bought from the store were stored in refrigerator. Two days later when I opened the basket, a tomato had rotted badly. I took out my foldscope and gently took a sample of the rotting tomato on a cello tape and fixed it on a slide. I could see a tangled mass of hyphae showing the cause of rotting to be a fungus.
On sliding the slide I could spot a large number of spindle shaped conidia, depicting the presence of Alternaria. I was able to see chain of conidia in an acropetalous succession at some loci. Some conidia were uniseriate, multicellular, while some were multiseriate, multicellular. The tomato were probably infected with Alternaria and led to post-harvest rot.
In literature I could gather up that sometimes over-riped tomatoes may develop black mold caused by Alternaria alternata. On fruits small, dark blotches or large sunken areas with soft, blackish fungal growth can be seen to be the cause of fruit rot. Sometimes black fungal growth may develop on pre-existing wounds or lesions leading to post harvest loss.