THE STEROL COMPOSITION OF POWDERY MILDEWS

The sterol composition of conidia of powdery mildews of apple (Podosphaera leucotricha), barley (Erysiphe graminis f.sp. hordei), and cucurbits (Sphaerotheca fuliginea) was very similar, and simple compared with that of other plant pathogenic fungi. Ergosta-5,24(24(1))-dien-3-beta-ol was the principal sterol in all three species, accompanied by much smaller amounts of 5-alpha-ergosta-7,24(24(1))-dien-3-beta-ol in apple and barley mildews, and cholesterol in the cucurbit mildew. All the ergostane derivatives found share the structural feature of a 24(24(1))-double bond, suggesting that in powdery mildews sterol side-chain biosynthesis does not proceed beyond the initial introduction of C-24(1).