Fire Blight Management in the Twenty-first Century: Using New Technologies that Enhance Host Resistance in Apple.

Abstract

Fire blight has been known as a destructive disease of apple and pear for over 200 years (3). The disease is caused by the bacterium Erwinia amylovora, which is capable of infecting blossoms, fruits, vegetative shoots, woody tissues, and rootstock crowns (Fig. 1). There are several distinct phases of the disease including blossom blight, shoot blight, and rootstock blight. The diversity of host tissues susceptible to infection, combined with the limited number of management tools available to control the disease, has made it difficult to stop or slow the progress of fire blight epidemics. Effective management of fire blight requires an integrated approach of several practices that are aimed at (i) reducing the amount of inoculum that is available to initiate new infections, (ii) imposing barriers to successful establishment of the pathogen on the host, and (iii) reducing host susceptibility to infection (1,55). Most fire blight management strategies developed during the twentieth century focused on the reduction of inoculum in the orchard and the use of antimicrobial treatments to prevent infection. Although increasing host resistance has been recognized as an important component of fire blight management, its application has been limited by a lack of resistant cultivars suited to commercial needs and by a lack of management practices that could effectively increase resistance. Recent advances have made it feasible to change this paradigm in the twenty-first century. First, apple rootstock breeding programs have developed size-controlling (often dwarfing) rootstocks that are resistant to fire blight and are currently becoming available for commercial use (43). Second, genetic engineering of commercial apple cultivars for increased fire blight resistance has been demonstrated, and transgenic apple plants are now undergoing field trials (2). Third, chemical treatments that enhance host resistance have been demonstrated to be useful in the control of fire blight (9,33,61). Although these technologies are at the early stages of development and are either not available or not proven in the marketplace, incorporating the use of host resistance into fire blight management strategies has become a realistic goal in the twenty-first century. This article describes recent progress in the development of new fire blight control technologies that enhance host resistance by chemical or genetic means.