Abstract
Helianthus annuus is a perennial plant native to the USA. Commonly known as a sunflower, H. annuus is grown ornamentally as well as for its oil and seeds. It can grow up to 8 feet in height. In August 2017, Helianthus annus ‘Lemon Queen’ leaves showing signs of powdery mildew were collected from the Pierce County master garden located at WSU Puyallup Research and Extension Center (47.2258oN, 122.4347oW). Signs of the powdery mildew included dense patches of white to greyish mycelia on the leaf surfaces. The fungus formed superficial branched hyphae with septa. The foot cells were straight and were followed by one to three short cells bearing conidia. The conidiophores contained short chains of up to 5 conidia. The hyphal appressoria were nipple shaped. The conidia were hyaline and ellipsoidal. Eudoidium type of conidial germination with a short germ tube developed. The conidia (N=55) ranged from 29 to 39 μm long (average=36 μm) by 16 to 24 μm wide (average=18.61 μm). Chasmothecia showed myceloid appendage...
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