GROWTH OF BIOLUMINESCENT XANTHOMONAS-CAMPESTRIS PV CAMPESTRIS IN SUSCEPTIBLE AND RESISTANT HOST PLANTS

Transposon Tn4431 was used to introduce luxCDABE the operon into a highly pathogenic strain of Xanthomonas campestris pv. campestris (X. c. pv. campestris), causal agent of black rot of crucifers. The bioluminescent strain was indistinguishable from the wild-type strain in pathogenicity tests and in planta growth characteristics. Movement and growth of the bioluminescent strain of X. c. pv. campestris in susceptible and resistant cabbage seedlings after wound or mist inoculation was followed over time with a liquid nitrogen-cooled, charge-coupled-device camera. Wound-inoculation resulted in significantly higher bioluminescence levels in the susceptible plant than in the resistant plant. More leaves became infected in the susceptibly host, and peak levels were reached after 5 days compared with 10-12 days in the resistant host. Peak bioluminescence levels were followed after 2-3 days by symptom development. Mist inoculation resulted in high bacterial population levels in mature susceptible leaves only. Hydathodes or wounds served as sites of infection in susceptible leaves, whereas entry was gained mainly through wounds on resistant leaves. Infection remained confined in and around damaged leaf areas in resistant leaves but spread rapidly through the vascular system of susceptible leaves.