Tomato plants in a subtropical field began to show progressive wilting, interveinal chlorosis, and root rot. The subsequent laboratory analysis indicated coenocytic hyphae along with the presence of thick-walled oospores. Additionally, the disease progressed rapidly in humid conditions. Which one of the following organisms is NOT likely to be responsible for the infection?

Correct option is C

The symptoms and lab findings point toward Oomycetes (water molds) because:
Coenocytic hyphae: Oomycetes have aseptate (coenocytic) hyphae, unlike true fungi which have septate
hyphae.
Thick-walled oospores: These are sexual spores of Oomycetes.
Disease thrives in humid conditions, which is typical for Oomycetes.
Analysis of each option:
-Pythium aphanidermatum: An Oomycete; causes damping-off and root rot in humid conditions → Possible.
-Phytophthora nicotianae: An Oomycete; pathogenic on many plants including tomato → Possible.
-Fusarium oxysporum: A true fungus (Ascomycete) with septate hyphae and produces chlamydospores, NOT
oospores → NOT likely.
Phytophthora infestans: Oomycete; causes late blight in tomato → Possible.