Xanthium italicum, Xanthium strumarium and Arctium lappa as new hosts for Diaporthe helianthi

Sunflower (Helianthus annuus) stem canker caused by Diaporthe helianthi is one of the most important sunflower diseases in Croatia. Until recently, sunflower was the only known host for D. helianthi. In our research carried out in the area of Eastern Croatia, isolates of Diaporthe/Phomospis were collected from Xanthium italicum, X. strumarium and Arctium lappa. Using morphological, cultural and molecular ITS rDNA data, isolates from these weeds were identified as D. helianthi. The following isolates were used in the pathogenicity test: one isolate originated from sunflower (Su5/04), three from X. italicum (Xa2, Xa3 and Xa5), two from X. strumarium (Xa9 and Xa12), one from Xanthium sp. (Xa13) and one from A. lappa (Ar3). According to the results, it was determined that isolate Xa5 (originated from X. italicum) was the most pathogenic to sunflower stems. The average length of the lesion was 11.3 cm. The lowest level of pathogenicity was found in Xa9 (isolated from X. strumarium). The length of the lesion was 0.1 cm.