Establishment of a procedure for bacterial spot inoculation and assessment in processing tomato field trials

Abstract

This study analyses two methods for establishing bacterial spot xanthomonad infection on processing tomatoes and three assessment methods to measure bacterial spot severity. These methods were evaluated at different crop stages under field conditions. The trials were conducted in 2010 and 2011. Three cultivars with known resistance to bacterial spot were used to validate the procedures. The plants were infected by spray inoculation with bacterial suspension, or by natural bacterial spot dissemination from previously inoculated plantlets of the susceptible cultivar Yuba, planted equidistant between the plant rows (indirect procedure). Disease severity was estimated by three methods according to the period of assessment: A) percentage of necrotic area of the third and fourth leaves of 12 plants per plot up to 30 days after transplanting; B) percentage of necrotic area of 24 leaflets per plot from 30 to approximately 60 days after transplanting, and C) a plot-based disease severity scale from 60 days after transplanting. Both inoculation procedures resulted in disease occurrence which was not as uniform as when plants were naturally infected by the inoculum source. Tomato cultivars were successfully differentiated in terms of quantitative resistance by the three assessment methods employed.