First Report of a Leaf Blight of Onion Caused by Xanthomonas spp. in Georgia

Abstract

In October of 2001 and 2002, a leaf blight was reported affecting Vidalia onion (Allium cepa) cvs. Pegasus and Sweet Vidalia, respectively, in one field each. Lesions on onion seedlings began as a water-soaked, tip dieback that gradually blighted the entire leaf. Symptoms on onion transplants appeared as elongated, water-soaked lesions that typically collapsed at the point of initial infection. In both cases, disease was very severe on seedlings, and disease incidence was 50% or more in both fields. Warm temperatures combined with overhead irrigation and above average rainfall likely enhanced the severity and spread of disease. Disease was not detected on more mature onions once cool, dry conditions occurred later in the season, and no significant economic loss occurred. Seed was tested from seed lots of the aforementioned cultivars and Xanthomonas spp. were not found. Diseased tissue was macerated in sterile, phosphate-buffered saline, and 10 μl of the resulting suspension was streaked on nutrient agar plates. Yellow-pigmented, gram-negative, rod-shaped bacteria were isolated routinely from diseased tissue. Bacteria were catalase-positive, cellulolytic, oxidase-negative, amylolytic, proteolytic, and utilized glucose in an oxidative manner. Analysis of whole cell, fatty acid methyl esters (FAME) using the Microbial Identification System (MIS, Sherlock version 3.1; MIDI, Inc., Newark, DE) identified four representative strains of the bacterium as a pathovar of Xanthomonas axonopodis (similarity indices 0.75 to 0.83). Known Xanthomonas spp. from onion from Colorado and Texas (1,2) had similar FAME profiles when analyzed by the MIDI system. Onion plants were grown under greenhouse conditions for 2 months and inoculated by injecting the base of a quill with 1.0 ml of bacterial suspensions (1 × 107 CFU ml-1) of the Xanthomonas sp. isolated from Georgia, and negative controls were inoculated with 1 ml of sterile water. Disease symptoms developed on plants inoculated with bacterial suspensions in 4 to 7 days and Xanthomonas sp. was isolated from the lesions produced. Disease symptoms occurred when the same suspension was sprayed on onion foliage. No symptoms occurred on plants inoculated with 1 ml of sterile water. To our knowledge, this is the first report of Xanthomonas spp. affecting Vidalia onions. References: (1) T. Isakeit et al. Plant Dis. 84:201, 2000. (2) H. F. Schwartz and K. Otto. Plant Dis. 84:922, 2000.

Multiplex Nested PCR for Detection ofXanthomonas axonopodispv. allii from Onion Seeds

“…allii (41). First identified in Hawaii (4), this pathogen emerged in the 1990s and 2000s in several countries, including Brazil (25), Venezuela (55), the Caribbean Islands (29), different states of the continental United States (16,28,47,50), Japan (17), the Republic of South Africa (52), and the Mascarene Archipelago (Mauritius and Réunion Islands) (33). Consequently, X. axonopodis pv.…”

Management of Xanthomonas Leaf Blight of Onion with Bacteriophages and a Plant Activator

“…Xanthomonas leaf blight of onion has since been reported in Barbados (26), the continental United States (17,22,30,32), Japan (19), Réunion Island (27,28), and South Africa (35). X. axonopodis pv.…”

Xanthomonas axonopodis pv. allii

“…North America: USA (California, Colorado, Georgia, Texas) (Isakeit et al ., ; Schwartz & Otto, ; Nunez et al ., ; Sanders et al ., ).…”

“…Infection of the aerial parts of onion by the pathogen may lead to a reduction in bulb size. Yield losses for onion bulbs ranging from 10% to 50% have been reported in Continental USA (Schwartz & Otto, 2000;Nunez et al, 2002;Sanders et al, 2003). Although not precisely documented, the impact of the disease may be higher in tropical countries.…”