Dimas Mejía-Sánchez

Leaf Stripe and Stem Rot Caused by Burkholderia gladioli, a New Disease of Maize in México

A new maize disease appeared in the State of Veracruz, Mexico during 2003-2004. Initial symptoms in the leaves were small, white-yellow, watery spots, which coalesced into dry necrotic stripes that were 0.3 wide and 8 cm long. Reddening sometimes developed on these leaves. Stems developed a rot in the crown. The flag leaf showed a rot and necrosis at the base, rolled inward, and dried out. Necrosis developed at the base of the corn ears and their growth was halted. A bacterium characterized by white colonies was consistently isolated from lesions on casamino acid peptone and glucose (CPG), Kings medium B, and nutrient agar media. Ten isolates were chosen for further characterization. Pathogenicity was confirmed in the greenhouse (25 to 30°C) on 45-day-old ASGROW 7573 maize plants by injection of bacterial suspensions (107 CFU/ml) at the base of the stem. Control maize seedlings were injected with phosphate buffer. Symptoms similar to those observed in the field were observed after 3 days on all inoculated plants but were not observed on control plants. Kochs postulates were fulfilled with reisolation of the inoculated strain from the inoculated tissues and confirmation was fulfilled by phenotypic characters and 16S rDNA sequences. The white colonies on CPG were slightly convex, shiny, circular with entire margins, gram negative, lacked arginine dihydrolase, did not produce fluorescent pigment on Pseudomonas F medium, and grew aerobically. The strains were able to utilize l-arabinose, d-mannitol, and cellobiose, but unable to utilize d-maltose and l-rhamnose. Gel hydrolysis was positive but starch hydrolysis was not positive. Colonies grew at 40°C. These characteristics are the same as those described previously for Burkholderia gladioli (3). The identity of these isolates was confirmed by 16S analysis with two universal primers, FD1 and RD1, for Eubacteria (2), which generate a 1,600-bp fragment. Two primers specific for the genus Burhkolderia, RHG-F and RHG-R that generate a 500-bp fragment (1) were also used for amplification. Comparison of sequences using Clustal W and Megaline, DNAstar software showed 100% similarity among strains isolated from the three counties (GenBank Accession Nos. EU161873 to EU161878) and 99% similarity of field isolates with B. gladioli in the GenBank database. To our knowledge, this is the first report of B. gladioli causing leaf stripe and stem rot of maize in Mexico. References: (1) J. J. Lipuma et al. J. Clin. Microbiol. 37:3167, 1999. (2) L. M. Rodrigues et al. Appl. Environ. Microbiol. 69:4249, 2003. 3) N. W. Shaad et al., eds. 3rd ed. Laboratory Guide for Identification of Plant Pathogenic Bacteria. The American Phytopathological Society, St. Paul, MN, 2001.