Drechslera tetramera, (Mck.inney) Subram and Jain, D. rostrata (Drechsl.) Richardson and Fraser and Alternaria alternata (Fr.) Keissler are reported in this work as grape¬vine leaf spot pathogens for the first time in Egypt. Their pathogenic abilities differed and depended on grapevine cultivar. Alternaria alternata was more pathogenic on Banaty cv. than Bez El-Anza one, however, D. tetramera and D. rostrata were more virulent on the above mentioned two cvs., respectively.
Relation between pectinolytic, (PG) cellulolytic (CX) and oxidative enzymes (polyphenol oxidase and peroxidase) activities of these fungi and its pathogenicity was more pronounced in vivo than in vitro. In case of inoculation with D. tetramera, the higher activities of PG and CX but the lower of polyphenol oxidase enzymes were detected in leaves of Banaty cv. than Bez El-Anza cv., the highest and lowest susceptible to these pathogens, respectively. Contradictory results were noticed with D. rostrata. No relation between peroxidase activity and pathogenicity of tested fungi was detected during this study.
Cellulolytic enzymes activities were more affected by different tested fungicidal treatment in vitro. In general the fungicide Topsin M-70 at concentration of 50 ppm. was checked PG and Cx enzymes activities of D. tetramera and D. rostrata to greater extent than Bayleton-25 or Copravit-50. However, Bayleton-25 was the best fungicide in case of A. alternata-PG and Cx-enzymes activities.
Activity of PG and Cx enzymes was gradually decreased with increasing pH value from 4.6 to 8.1. In general, at the same pH value, more enzyme activity was detected in fungal filtrates of 14 days than in 7 or 21 days-old cultures.