In recent years, Diplodia bulgarica A.J.L. Phillips, J. Lopes & S.G. Bobev was identified as the main causal agent of apple tree decline in Iran. This fungus causes stem and trunk cankers, dieback, bark discoloration, gummosis, scaling-off of the bark and fruit rot in the west and northwest apple orchards of Iran. The disease was often prevalent in trees more than 15-years-old that were suffering from environmental stresses such as drought and nutrient deficiency. To evaluate the response of apple tree cultivars to this pathogen, six commercial cultivars (Golden Delicious, Red Delicious, Granny Smith, Red Starking, Braeburn, and Gala) and three local cultivars (Golab, Qara Yapragh, and Turkaman) were assessed under field conditions. The results confirmed that all cultivars are susceptible to Diplodia bulgarica, but mean lesion lengths differed significantly between cultivars (P=0.01). The largest lesions were observed on Braeburn, Red Delicious, and Red Starking cultivars, thus these cultivars were considered to be the most susceptible. Lesion lengths on Qara Yapragh, Turkaman, and Golden Delicious were significantly smaller than on all other cultivars and these were considered as moderately resistant to Diplodia bulgarica in Iran. To our knowledge, this is the first report on the response of apple tree cultivars to this devastating pathogen.
