RESISTANCE OF STRAWBERRY TO ROOT ROT AND PETIOLE BLIGHT CAUSED BY GNOMONIA FRAGARIAE

Strawberry root rot and petiole blight caused by Gnomonia fragariae Kleb. is a recently described disease. Cultivar resistance or susceptibility and the mechanisms behind it are unknown. Initially, to identify resistance sources, disease severity and development was evaluated on 55 strawberry genotypes, including commercial cultivars and hybrids, for two years under field conditions. The evaluation was done at a site with a long history of high disease severity. Highly tolerant to very susceptible genotypes were identified. Oxidative enzymes were evaluated for their involvement in the defensive reactions of susceptible and resistant strawberry genotypes. The activity of peroxidase and polyphenol oxidase was evaluated in strawberry leaves and roots of non-inoculated and inoculated plants 12, 24 and 48 h after inoculation. Activity of both enzymes was highest in leaves and roots of inoculated resistant strawberry cultivars. Polyphenol oxidase activity in resistant cultivars increased 12 h after inoculation, whereas peroxidase activity after 24 h. Changes in oxidative activity indicated involvement of peroxidase and polyphenol oxidase in the resistance mechanisms of strawberry to Gnomonia fragariae.