Effect of temperature on the incubation period and leaf colonization in bacterial blight of Anthurium

Effect of temperature on leaf colonization in anthurium blight was studied using a bioluminescent strain of Xanthomonas campestris pv. dieffenbachiae. In a susceptible cultivar, colonization of leaf tissues (monitored by dete ction of bioluminescence) and symptom development (assessed visually) advan ced rapidly at higher temperatures. For a susceptible cultivar, there was a linear relationship between degree-days and percent leaf area colonized by the pathogen, indicating that leaf colonization in a susceptible cultivar was a direct function of the cumulative effect of temperature. The degree-d ay intercept of the regression line represented the time from inoculation t o detection of bioluminescence, and the slope indicated the increase of lea f colonization per degree-day. There also was a linear relationship between the logarithm of degree-days and the logarithm of percent leaf area showin g visible symptoms in a susceptible cultivar. The degree-day intercept of t his relationship represented the incubation period (about 500 degree-days). The degree-days required to detect bioluminescence was not considerably di fferent between susceptible and resistant cultivars. However, the subsequen t rates of leaf colonization were significantly lower for a resistant culti var than for a susceptible cultivar in all temperature regimes. The results suggest that multiplication of the pathogen in the leaf tissues is optimiz ed in the susceptible cultivar. In contrast, in the resistant cultivar, the defense mechanisms overshadow the temperature effect. The differential res ponse to temperatures may be an additional indicator of cultivar susceptibi lity.