BACTERIAL-BLIGHT OF CARNATION CAUSED BY PSEUDOMONAS-WOODSII AND SUSCEPTIBILITY OF CARNATION CULTIVARS

Pseudomonas woodsii was shown to be the cause of a blight of carnation on 10 Maui farms during 1989 and 1990. Small, water-soaked, yellow sp ecks that appeared 6 days after inoculation were the initial symptoms on potted plants. When plants were inoculated with 2.9 X 10(6) cfu/ml, the specks appeared in 6 days and enlarged to 2- to 3-mm-diameter dis crete spots 4 days after initial symptoms were visible; at 4.5 X 10(8) cfu/ml, however, lesions coalesced, causing extensive blight. Plants inoculated with 10(6) to 10(8) cfu/ml produced comparable numbers of l esions when incubated for 24-48 hr in a moist chamber or outdoors at a mbient relative humidities. The lowest inoculum level to initiate dise ase was 2.9 X 10(3) cfu/ml. Streptomycin sulfate at 250 and 500 ppm a. i., oxytetracycline at 204 and 407 ppm a.i., and fosetyl Al at 4,800 a nd 9,600 ppm a.i. significantly reduced the number of leaf spots, but treatments did not economically control the disease. Of 66 cultivars e valuated in the field, Cal Red and Cal Improved White showed high dise ase resistance.