CORRELATION BETWEEN FIRE BLIGHT RESISTANCE AND PHENOLIC LEVELS IN PEARS

Flowers and ripe fruits of fire blight-susceptible, 'Bartlett' and -resistant, 'Elliot' pears were inoculated with bacterial suspensions of Erwinia amylovora (Burr.) Winslow et al. Four of ten spurs of 'Elliot' became infected, whereas all ten 'Bartlett' spurs became diseased. The infection spread into larger limbs in 'Bartlett', hence, more bearing surface for subsequent years was lost compared to pruning losses from 'Elliot' Ethanolic extracts from blight-resistant, ‘Winter Nelis’ and 'Elliot' and its susceptible and resistant siblings, seedling 5-1 and 5-8, respectively, 'Beurre Bosc' and 'Bartlett' were tested for their capacity to inhibit the bacteria in vitro. A good correlation was established between the phenolic and leucoanthocyanidin contents in fruit extracts and relative resistance to the organism. A similar trend was found between extracts from young shoot tips and resistance but there were a few exceptions.