Bacterial Blight in Carrot Seed Crops in the Pacific Northwest

Lindsey J du Toit; Fred J Crowe; Mike L Derie; Rhonda B Simmons; Gary Q Pelter

doi:10.1094/PD-89-0896

Carrot (Daucus carota subsp. sativus) seed crops in Oregon and Washington were surveyed in 2001-02 and 2002-03 for development of Xanthomonas campestris pv. carotae, causal agent of bacterial blight. For each state and season, 20 plants were sampled from each of 7 to 12 direct-seeded crops twice in the fall or winter and three times from spring to summer; and from each of 2 to 4 steckling (root-to-seed) crops three times from spring to summer. X. campestris pv. carotae was detected in 1 of 15 and 6 of 32 stock seed lots planted in the fall in Oregon and Washington, respectively, and in 2 of 6 steckling shipments planted in each state in the spring. The pathogen was detected at 102 to 108 CFU/g foliage in 1 of 22 and 10 of 14 direct-seeded crops within 2 months of planting in 2001 and 2002, respectively. The prevalence of X. campestris pv. carotae then increased through the season in most seed crops, although bacterial blight symptoms were not observed until April in Oregon and July in Washington in both seasons. In August 2002 and 2003, X. campestris pv. carotae was detected in all 10 and 13 crops surveyed in Oregon, respectively; and in 11 of 12 and 7 of 10 crops in Washington, respectively. The pathogen was typically less prevalent in steckling versus direct-seeded crops. X. campestris pv. carotae was detected in 20 of 22 and 19 of 23 harvested seed lots in Oregon and Washington, respectively, at populations ranging from 1.3 × 101 to 1.4 × 108 CFU/g seed. Airborne X. campestris pv. carotae, detected ≤1,600 m downwind of crops being threshed in Oregon in September of 2003 and 2004, may provide a source of inoculum for newly planted seed crops between overlapping biennial seasons for carrot seed production. Despite the prevalence of this pathogen in the Pacific Northwest, carrot seed lots free of X. campestris pv. carotae were detected, demonstrating the ability to produce clean seed in this region by adhering to recommended practices for management of bacterial blight. Carrot seed crops in Oregon and Washington provide up to 75% of the U.S. and 50% of the world supply of carrot seed. Seed crops in these states were surveyed in 2001-02 and 2002-03 to identify sources of inoculum of Xanthomonas campestris pv. carotae, causal agent of bacterial blight, and to monitor development of the pathogen in the biennial cropping system. The pathogen was detected in 7 of 47 stock seed lots planted in the fall, and 4 of 8 steckling (vernalized root) shipments planted in the spring. The bacterium was detected in some crops within 2 months of planting. Prevalence of X. campestris pv. carotae increased throughout the season, but symptoms were not observed until April in Oregon and July in Washington. By August, the pathogen was detected in all crops surveyed in Oregon and in 70 to 92% of the crops surveyed in Washington. X. campestris pv. carotae was detected in 39 of 45 harvested seed lots. The bacterium was also detected in aerosolized debris ≤1,600 m downwind of crops being threshed. Airborne inoculum may infect newly planted crops between overlapping biennial seasons. Despite the prevalence of this pathogen, seed lots free of X. campestris pv. carotae were detected, demonstrating the ability to produce clean seed by adhering to recommendations for management of bacterial blight, including planting clean stock seed or stecklings, rotating out of carrots for 3+ years, incorporating residues into the soil promptly after harvest, isolating seed crops spatially and temporally (between biennial seasons), avoiding overhead irrigation, and applying copper bactericides when conditions are conducive for this disease.

Bacterial Blight in Carrot Seed Crops in the Pacific Northwest

Files and links (1)

Abstract

Metrics

Details