COMPETENCE OF PEAR SHOOT AND FRUIT WOUNDS FOR ERWINIA AMYLOVORA INFECTION
V. Babini, U. Mazzucchi
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.