Blister spot is a bacterial disease of apple fruit caused by Pseudomonas syringae pv. papulans. This disease is of economic importance mainly on the cultivar ‘Mutsu’ (‘Crispin’) but can be seen on ‘Golden Delicious’ grown adjacent to ‘Mutsu’. Even though fruit grow to maturity and no detectable yield loss occurs, severe infection results in ugly fruit and greatly reduces fresh-market quality.
| Figure 1. Blister spot on ‘Mutsu’ fruit. Photo: T. van der Zwet, USDA. |
|---|
 |
Blister spot lesions are first noticeable …