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-3β-ol was the principal sterol in all three species, accompanied by much smaller amounts of 5α-ergosta-7,24(24 1)-dien-3β-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.