First Report of Cotton Lint Rot by Pantoea agglomerans in Georgia.

Abstract

In September, 1996, cotton bolls of NuCotn 35B, DPL 90, Hart 404, NuCotn 33B, and DPL 5415 grown in three eastern Georgia counties were found to contain internal lint rot within single or multiple locules. No external boll damage was observed. Damage was always more severe on NuCotn 35B. Internal lint damage occurred in bolls tips that formed abnormal fissures or openings nearest the sutures. Such bolls often contained an additional locule. In one field of NuCotn 35B, over 30% of the bolls containing the abnormal tip morphology had locular lint rot. The abnormal boll morphology described previously as supernumerary carpel syndrome (SCS) has been associated with internal lint rot (2). Rotted lint within the locules was usually reddish brown mixed with yellow and olive to olive-brown. Gram-negative bacteria were isolated from infected bolls on nutrient agar and shown to be Pantoea agglomerans on the basis of rod shape, yellow pigmentation, and utilization of glucose both in an oxidative and fermentative manner without gas production. These characteristics are typical of bacterial strains belonging to the Enterobacteriaceae (facultative anaerobes). Even though bacterial taxonomists are uncertain about the species identification of certain genera within this family, strains 92-52D and 92-52E, isolated from NuCotn 35B, were identified within the complex P. agglomerans (Ewing and Fife) Gavini, Mergaert, Beji, Mielcarek, Izard, Kersters, and De Ley (=Enterobacter agglomerans;=Erwinia herbicola (1). Previously, P. agglomerans was reported to cause lint rot of cotton locules associated with SCS and stinkbug (Euschistus impictiventris) injury (2). In California, the lint rot bacterium was isolated from the stylar canal, especially when SCS was present. To confirm pathogenicity of the isolates, 30 bolls of NuCotn 35B were excised, brought into the laboratory, and surface disinfested with 70% ethanol. Bolls were inoculated by dipping sterile dissection needles in bacterial colonies from 24-h cultures on nutrient agar and immediately puncturing (3- to 7-mm depth) 10 bolls per strain. An additional 10 bolls were wounded with sterile needles for comparison. The bolls were placed in a moist chamber and incubated at 28°C for 72 h. Locule damage was rated on a 0 to 3 scale in which 0 = no damage, 1 = trace damage, 2 = moderate discoloration and deterioration, and 3 = total discoloration and deterioration of the fiber. Bolls inoculated with strains 96-52D and 96-52E had mean boll rot indices of 2.0 and 1.5, respectively, and Koch's postulates were completed for both strains. The noninoculated bolls had a discoloration indice of 0.6, but 7 out of 10 were rated as 0. The infections of the three bolls by P. agglomerans may have been caused by natural inoculum that survived the surface disinfestation. These findings are the first report of P. agglomerans causing lint rot of bolls with SCS in Georgia.