Determination of fire blight (Erwinia amylovora) susceptibility in Turkey’s Cydonia oblonga Mill. Germplasm

Fire blight (Erwinia amylovora) is one of the biggest challenges in the production of quince (Cydonia oblonga Mill.) in Turkey, and the lack of effective control methods emphasizes the need for resistant varieties of this species; therefore, testing the susceptibility levels of the germplasm is necessary to create breeding programs that ensure resistance to this disease. The aim of our study was to determine the susceptibility levels of the Turkey quince germplasm. To that end, 56 genotypes were tested using three inoculation experiments in a climate-controlled greenhouse using a mixture of three virulent isolates. Resistance/susceptibility levels were determined according to the percentage of shoot length that was blighted (% SLB), which varied between 24.46 and 61.54%. The main effects of genotype and inoculations were statistically significant; interactions between genotype and inoculations were not, which indicated that genotypes developed different susceptibility responses independent of inoculations and greenhouse conditions. The results of the experiments were averaged, and the germplasms were grouped according to the Gardner scale as “resistant”, “medium susceptible”, and “susceptible” and divided into 6 groups (a-f) after statistical analyses. More detailed classification has been obtained by statistical analyses, so it is recommended that genotypes used in breeding studies must be classified statistically in addition to the classical classification. Genotype 2168 was the most resistant (24.69%) and had very similar SLB values in all experiments, which indicated that resistance is stable in only the most resistant genotypes. Ayva B 35 and Quince A rootstocks had 29.11 and 37.16% SLB, respectively. Altin 35 (28.58%), Ege 25 (30.49%), and Zeybek 35 (30.91%) cultivars and Ayva B 35 rootstock, which are developed through selection breeding, were found to be more resistant. The Turkey quince germplasm that was resistant to fire blight can be used as a breeding parent or registered as a fire blight resistant variety or rootstock. The results of this study have encouraged the onset of crossbreeding studies on fire blight resistance.