Phialophora asteris f. sp. helianthi, a New Pathogen of Sunflower in Italy. L. Tosi, Institute of Plant Pathology, University of Perugia, Borgo XX Giugno, 74,06100 Perugia, Italy. A. Zazzerini, Institute of Plant Pathology, University of Perugia, Borgo XX Giugno, 74,06100 Perugia, Italy. Plant Dis. 79:534-537. Accepted for publication 18 January 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0534.

A wilt disease was observed during the summer of 1993 in a sunflower field near Perugia in central Italy. The disease was characterized by yellowing of leaves as plants approached flowering. Large areas of the leaves turned light green, usually beginning at the apex and margins and extending inward. Subsequently, leaf margins turned necrotic, and diseased plants were stunted with smaller heads. Our trials proved that this disease was caused by Phialophora asteris f. sp. helianthi. The fungus was examined for colony morphology, temperature growth responses, and pathogenicity. Significant differences were observed among various culture media. Best growth and profuse sporulation were obtained on carrot and Czapeck agars added with peptone. The optimum temperature for growth was 25 C; temperatures of 5, 10, 15, and 30 C greatly reduced colony growth and sporulation. No growth was observed at 35 C. Significant differences in susceptibility to P. a. helianthi were observed in 17 sunflower cultivars tested in greenhouse trials; sunflower lines HA 335, 803-1 (=DM-5), HA 89, HARI, and RHA 274 were the most resistant. This is the first report of the disease in Italy and Europe.

Keyword(s): Phialophora yellows, wilt