Selections for Resistance against Fire Blight in Young F1 Hybrid Pear Seedlings in Turkey

Fire blight, caused by pathogenic bacterium Erwinia amylovora, is a serious disease of pear, with few effective disease management strategies. Therefore, it is very important to strive towards the selection of new resistant cultivars to fire blight. With this purpose, different crosses have been made between resistant cultivar 'Magness' and other resistant or susceptible cultivars and cultigens ('Akca', 'Ankara', 'Bursa', 'Conference', 'Guz', 'Kaiser Alexandre', 'Kieffer', 'Moonglow', 'Tas'). The susceptibility levels of the resulting hybrids were determined by artificial inoculations by Erwinia amylovora in greenhouse conditions. In pathogenicity tests, 10(8) CFU/ml populations of seven E. amylovora strains, isolated from different cities in Turkey, were used to infect the shoots of hybrid plants. Eight weeks after inoculations, the percentage of the necrotic lesion to the total length of the shoot was calculated for each shoot. The experiments were performed twice in August 2010 and May 2011. The average of two experiments was used to calculate the percentage disease severity. Susceptibility was scored by binning the percentage into five distinct classes of increasing susceptibility (A to E). Among 1242 young F-1 hybrid seedlings inoculated, 31.64% of them showed "very low susceptibility" (A), 8.62% displayed "low susceptibility" (B), 18.60% were "moderate susceptibility" (C), 30.27% were "high susceptibility" (D), 10.87% showed "very high susceptibility" (E), and 85 of hybrids were completely destroyed by the pathogen. The 393 "very low susceptibility" and 107 "low susceptibility" F1 hybrids were planted in Eskisehir, in Central Turkey, for screening for agronomical and pomological characteristics.