Differential susceptibility of Anthurium cultivars to bacterial blight in foliar and systemic infection phases

Susceptibility of anthurium cultivars to systemic infection by the bacterial blight pathogen, Xanthomonas campestris pv. dieffenbachiae, was examined using a bioengineered bioluminescent strain (V108LRUH1) and compared with susceptibility to foliar infection. Eight cultivars with different levels of susceptibility to foliar infection were evaluated for their susceptibility to systemic infection. Petioles of second youngest leaves cut near the main stem were inoculated with strain V10LRUH1, and subsequent movement of this bacterium into other petioles was monitored by observing bioluminescence from the plants. The actual extent of systemic movement was determined by reisolating V108LRUH1 from dissected segments of the remaining petioles. In susceptible cultivars, the pathogen advanced very rapidly and nearly reached the distal end of petioles. In resistant cultivars, the pathogen was detected in none (or very few) of the petiole segments. However, the susceptibility ranking among the tested cultivars for systemic infection did not always correspond to the ranking determined for foliar infection: i.e., one cultivar that was susceptible to foliar infection was highly resistant to systemic infection, and vice versa. This suggests that cultivar susceptibility of anthuriums to bacterial blight may differ depending on the phase of disease progression, and thus evaluation for both disease phases is essential for complete understanding of cultivar susceptibility.