Pyrenophorol is a simple macrocyclic dilactone produced by a number of species of pathogenic fungi, including Byssochlamys, Stenphyllum, Alternaria and Drechslera, first reported in the late 1960s. Pyrenophorol exhibits antibiotic, herbicidal and anthelmintic properties, and is a weak inhibitor of propyl endopeptidases. Pyrenophorol inhibits seed germination but once the seed is germinated, pyrenophlorol enhances root development but causes abnormal chlorophyll retention in leaf sections.