Investigations were carried out by gas-liquid components increased with time. Based
The potential of herbaceous weeds commonly growing in or adjacent to cucurbit crops to serve as alternate hosts and overwintering reservoirs of Erwinia tracheiphila, a causal agent of cucurbit wilt, was investigated. Methods for isolation, maintenance, long-term storage, and detection of E. tracheiphila from infected plants were developed. E. tracheiphila was consistently detected by enzyme-linked immunosorbent assay (ELISA) and reisolated from infected, susceptible, cucurbit species. When six common herbaceous weed species were inoculated, E. tracheiphila was detected in 49% (combined species) of the plants by ELISA 3 weeks after inoculation. However, we were unable to reisolate E. tracheiphila from these plants by standard techniques. Immunoaffinity isolation with a sensitivity of 2 CFU per sample also failed to recover E. tracheiphila from weed species. Comparisons of cucumber and goldenrod inoculated with live or formaldehyde-killed E. tracheiphila indicated that immunoassays could detect nonviable E. tracheiphila systemically spread in plants 3 weeks post-inoculation. In these tests, the pathogen was reisolated only from cucumber plants inoculated with live E. tracheiphila. Although we could reproduce serological evidence of E. tracheiphila antigen in the weeds investigated, our results do not support the hypothesis that E. tracheiphila can infect, survive in, or overwinter in the weed species tested.
During a period of 10 months, weekly samples were taken of rotted banana crowns to determine the microorganisms associated with rot. On a total of 648 crowns, Cephalosporium sp. occurred on 93%, Verticillium theobromae 81%, Fusarium roseum 'Gibbosum' 80%, F. moniliforme 14%, Botryodiplodia theobromae 12%, and Gloeosporium musarum 3%. Isolates of these organisms from green crowns, bracts, flowers, and petioles of the banana plant were able to rot crown segments in laboratory tests. Cephalosporium sp. has been shown for the first time to be capable of causing crown rot. Cultures of F. roseum from the air, grass, and Drosophila sp. were also pathogenic. A synergistic effect on rotting was demonstrated between F. roseum and bacteria isolated from crown tissue. Crown rot incidence fluctuated during the sample period, but this could not be correlated with changes in the occurrence of causal organisms present on the crowns.
Pseudomonas corrugata, the causal agent of a serious disease of roots, rotted onion scales and produced necrotic lesions on lettuce leaves, greenhouse-grown tomato plants in England, was isolated from healthy but potato tuber tissue was not rotted. Attempts to isolate strains of the roots of greenhouse-grown alfalfa plants in the USA. Inoculations of organism from field-grown alfalfa plants failed. Therefore, its role in root bacterial strains from both alfalfa and tomato into tomato stems induced and crown diseases of alfalfa was not determined. This is the first report on symptoms similar to those originally described for the disease. Strains from the occurrence of P. corrugata in the USA. both sources caused localized necrosis when injected into alfalfa stems and In 1974 1 reported (10) the isolation of pathogenic bacteria Pathogenicity tests.-For these tests, the bacteria that had been resembling Pseudomonas cepacia from surface-sterilized cross stored in sterile tap water were transferred to YDCA (glucose, 20 g; sections of healthy alfalfa roots that were being used to study the yeast extract, 10 g; CaCO 3 , 20 g; and agar, 15 g; in 1 L of H 2 0) and interactions between strains of Corynebacterium insidiosum. The allowed to grow for 48 hr before use. The roots of 1-yr-old alfalfa bacteria produced a dark blue pigment which was evident both in plants (Medicago sativa L. 'Saranac') were freed of soil by washing. the colonies and in the root tissue beneath the colonies. That report Three 5-mm diameter roots of each plant were inoculated by listed some similarities with P. cepacia, such as production of wounding with a teasing needle smeared with bacteria. Surface yellow pigment, nonfluorescence, presence of poly-/3-hydroxy-water from sterile medium was used as a control. Each isolate was butyrate granules, and showing an oxidase positive reaction. The inoculated into four separate plants which were transplanted into alfalfa strains differed from P. cepacia in being unable to grow at 41 sterile sand and covered with a plastic bag for 24 hr. Five days later C and being able to break down gelatin rapidly. the roots were washed free of sand and evaluated for disease A similar bacterial strain, isolated from a diseased tomato stem, development. was described by Scarlett, et al (15) who concluded that the new The stems of greenhouse-grown alfalfa, tomato (Lycopersicon strain was different from the P. cepacia group. They established a esculentum Mill.), and onion (Allium cepa L.) were inoculated by new species, Pseudomonas corrugata Roberts and Scarlett, and injection with a suspension of two of the alfalfa strains and NCPPB designated isolate NCPPB 2445 as the type culture. 2445. The inocula in tap water were adjusted to a constant level of For this study an isolate of the type culture was obtained through 20% transmission at 420 nm ("-10 X 10' cells per ml) before use. The the courtesy of Pauline Roberts. plants were bagged for 24 hr and left on a greenhouse bench. This report is a summary of different biochemical, ...
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