The incidence of onion purple blotch disease was
investigated at Assiut Governorate, Egypt during 2011.
Lesions with typical symptoms of the disease were colonized
by Alternaria porri, Stemphylium vesicarium or mixtures of
the both pathogens comprising 2.6, 39.8 and 57.6 % of
samples, respectively. Four isolates were selected for virulence
evaluation according to the nature of isolation, whereas
two isolates were individually associated with the diseased
samples and two isolates were collectively recovered. Individually,
A. porri AUMC9301 and AUMC10453 showed
high virulence contributing 81.25 and 78.13 %, respectively.
Also, S. vesicarium AUMC10512 and AUMC10519 exhibit
severity comprising 37.50 and 25.00 %, respectively. On the
other hand, mixture of A. porri AUMC10453 and S. vesicarium
AUMC10519 exhibited highest virulence (91.50 %).
In conclusion, this investigation proved that onion plants
showing purple blotch symptoms mainly colonized by both
A. porri and S. vesicarium. Consequently, increase in the
disease may be attributed to the association between these
pathogens.