The Effect of Chitinase on Didymella applanata, the Causal Agent of Raspberry Cane Spurlight

In vitro and in vivo studies were conducted to assess the efficacy of the two microbial chitinases Chi I (from Streptomyces sp.) and Chi II (from Serratia marcescens) on Didymella applanata (Niessl.) Sacc., the fungus which causes spur blight of raspberry (Rubus idaeus L.). D. applanata was isolated from canes of diseased raspberries in a plantation in Novosibirsk, Russia. In vitro, the effective concentration of Chi I that reduced the growth of D. applanata was 0.4 U/ml (p = 0.05), but Chi II had no influence on the growth of the fungus in medium. In inoculation experiments on raspberry canes, both chitinases at the rate 0.5 U/ml reduced fungal development. In plantation where canes were inoculated after spraying with chitinase, fruiting bodies of fungus failed to form in all enzyme treatments, whereas a significant number of these fungal fruiting bodies (12.8 per cm²) developed in control treatments lacking chitinases spraying. The chitinases reduced the size of lesions and limited the infection of internal tissues of canes. Field testing of Chi I under natural conditions showed a significant suppression of the independent spur blight. These studies form the basis for further evaluation of ecologically benign control measures for raspberry spur blight.