Insights into epidemiology and control of diseases of annual plants caused by the Pseudomonas syringae species complex

Abstract

The plant pathogenic Pseudomonas syringae species complex (Pssc) causes diseases of hundreds of species of monocots, herbaceous dicots and woody dicots worldwide. On annual plants, reports of disease caused by the Pssc have markedly increased in the last years. Hence, efforts are needed to mitigate the consequences of increasing disease outbreaks and to understand the underlying epidemiological factors. Here, we have reviewed the literature to highlight the salient features of the Pssc as pathogens of annual plant species and to underscore what remains unknown about the diseases they cause. The major points are as follows: (1) Since only the beginning of this century, 72 reports of disease outbreaks in 20 countries have been associated with the Pssc on over 40 annual plant species; (2) disease incidence caused by the Pssc on annual plants ranges from 50 to 100 % in epidemic years; (3) seed infestation is the main cause of long-distance pathogen dissemination; (4) foliar disease symptoms are very common on annual plants although the Pssc causes symptoms on fruits of bean, cantaloupe, cucumber, okra and tomato; (5) environmental factors such as rainfall and humidity have important roles in the Pssc disease epidemiology; (6) several new disease reports contradict the concept of the so-called pathovar, thereby raising the question of whether strains in the Pssc are mostly generalists rather than specialists as currently believed; and (7) disease control of annual plants is frequently based on approaches integrating biological, chemical and cultural measures with available plant resistance.