AbstractThe capacity of Monilinia laxa (Aderh. et Ruhl.) Honey to induce peach twig blight was lost in an albino mutant and in a wild‐type strain of the pathogen treated with pyroquilon, a melanin biosynthesis inhibitor. Pyroquilon (10 ù ml−1) inhibited melanin biosynthesis but did not inhibit mycelial growth of the pathogen or the albino mutant in vitro. These observations indicate that the compound interferes in some manner with the infection process of host cells.