Glomerella cingulataand bitter rot of apple

Abstract

Abstract Infection of undamaged apples by Glomerella cingulata (Stonem.) Spaulding & Schrenk was studied in the laboratory. Appressoria were formed in about 8 h at 21°c. Apples had to be wet for 2–3 days for penetration hyphae to establish infection. The length of this period would account for severe bitter rot epidemics occurring only in years of abundant rain; and also for lesions being mainly on the exposed faces of apples, which are more readily wetted than shaded faces. The period from inoculation to sporulation in the laboratory was about 11 days. In the orchard, lesions did not appear on apples until the crop was approaching maturity. It is postulated that secondary spread of the disease is usually restricted by the shortness of the period between appearance of fruit lesions and the time when fruit is harvested for cool storage. Disease records taken over 4 years indicated that each tree is its own main source of primary inoculum for fruit infection. Captafol sprays early in summer reduced the amount of fruit infection that developed 2 months later. It is suggested that this was due to reduction of primary inoculum, the saprophytic phase of G. cingulata in the trees.