COMPETENCE OF PEAR SHOOT AND FRUIT WOUNDS FOR ERWINIA AMYLOVORA INFECTION

Abstract

Pruning and artificial ‘hailstone wounds’ on pear shoots and needle wounds in fruitlets were contaminated every 6 hours, starting from a few seconds after injury, and up to 66 h with known inoculum doses of a virulent strain of Erwinia amylovora. A single wound was made on each shoot and fruitlet. Cankers on shoots and brown areas on fruits caused by successful infection were observed, respectively, 20 and 8 days after contamination at 25±2°C. The shoot wounds were progressively less competent for infection as the interval increased between wounding and contamination. The largest reduction in competence occurred in the first 24 h after wounding (from 80-85% successful infections to approximately 10-20%). The pear shoot pruning wounds were still competent after 48 h and up to 60 h, although less than 5% of inoculations were successful. Acropetal cankers developed above the ‘hailstone wounds’ between 35 and 66 h after wounding. Wounds on fruits kept in a damp chamber remained competent longer than those on young pear tree shoots kept at 50-90% relative humidity. The variation in competence in the pear shoot and fruitlet wounds is discussed and compared with other bacterial host-pathogen systems.