Role of Infected Plant Parts in Development and Survival of Fire Blight of Pome Fruits (Erwinia amylovora)

In order to evaluate the role of infected host parts, cankers, etc. in dispersion and survival of fire blight of pome fruits, thirteen fruit gardens throughout Semnan province were inspected during 2007-2008. Infected plant parts were collected from different localities and the causal agent was isolated from different samples using SNA (sucrose nutrient agar) medium following standard methods. Results indicated that epiphytic population of bacteria at a range of 3×103–10 cfu/flower in pear and 3×106 – 1.7 ×107 cfu/flower in quince caused blossom blight during rainy days with moderate temperature. It was found that except apple trees of Tash region, pome fruits of remaining regions were infected with the disease. Higher disease incidence occurred in quince 88%), pear (55%) and apple (24%) respectively. It was also found that the role of different plant parts in maintenance of fire blight was directed by weather in such a way that total plant parts of quince and specially their cankers caused highest disease incidence. It was found that the disease can be transmitted to the next year by different infected plant parts of pome fruit trees while one year old cankers of trunks and main branches had the most important role in this connection.