Xanthomonas hortorum pv. carotae

From ISTA 7-020 method: 

On MKM after 4-6 days, Xhc colonies appear light yellow-cream, light brown to peach yellow, glistening, round and 2-4 mm in diamter.

On MD5A after 7-8 days, Xhc colonies appear straw yellow, glistening, round smooth, convex with entire margins and 2-3 mm in diamter.

On mTBM after 7-8 days, Xhc colonies appear white or yellow or white-yellow, glistening, round, smooth, convex with entire margins, 1-2 mm in diamter and surrounded by a large clear zone of casein hydrolysis. Casein hydrolysis on mTBM is not always present. 

On YDC, suspect colonies are subcultured and will appear pale yellow and mucoid after 48-72 hr incubation at 28C.

Pathogenicity test on susceptible carrot cultivar (e.g. cv. Napoli) at 3-4 true leaf stage. Typical Xhc symptoms first appear as small, irregular yellowish water-soaked areas with a tiny, light brown spot in the center of innoculated leaves. Later, affected areas enlarge, become brown, and are often surrounded by a yellow halo.