Detection and elimination of seed-borne bacterial pathogens for the production of clean seed in bean (Phaseolus vulgaris L.)
| MSI00P3354 | |
| Mawlah, N. | |
| University of Mauritius, Faculty of Agriculture, Reduit | |
| Detection and elimination of seed-borne bacterial pathogens for the production of clean seed in bean (Phaseolus vulgaris L.) | |
| Thesis, MPhil | |
| Thesis | |
| 1999 | |
| 223 p.: 22 tbls, 11 figs, 26 pl. | |
| En | |
| En | |
| Characterization of 114 bacterial blight isolates from bean revealed that 70 of them were Pseudomonas savastanoi pv. phaseolicola, 36 Xanthomonas campestris pv. phaseoli and 8 Xanthomonas campestris pv. phaseoli var. fuscans. The brown spot bacterium Pseudomonas syringae pv. syringae was not found. The cultural, biochemical, and physiological properties of the isolates were typical of the respective pathogens. The thermal death point of Pseudomonas savastanoi pv. phaseolicola, Xanthomonas campestris pv. phaseoli and Xanthomonas campestris pv. phaseoli var. fuscans was 55 oC, 53 oC and 50 oC respectively. Antisera were raised against Pseudomonas savastanoi pv. phaseolicola and Xanthomonas campestris pv. phaseoli in rabbits to investigate serological relationship among the isolates and for detection. In agar double-diffusion tests, no serological difference was found among isolates of Pseudomonas savastanoi pv. phaseolicola and those of Xanthomonas campestris pv. phaseoli with their respective antiserum. In indirect ELISA, with an antiserum dilution of 1:1000, the threshold of detection was 1 x 106 cells/ml for both pathogens. A higher sensitivity of 1 x 104 cells/ml was obtained in indirect immunofluoresent microscopy (IF) for both Pseudomonas savastanoi pv. phaseolicola and Xanthomonas campestris pv. phaseoli. The three serological methods (agar double-diffusion, ELISA and IF) were applied for the detection of the two bacteria from leaves, pods and seeds. Two of the techniques, ELISA and IF could successfully detect the pathogens from diseased tissues after exudation in sterile distilled water and centrifugation. No cross-reaction was observed in ELISA and IF with the Pseudomonas savastanoi pv. phaseolicola and Xanthomonas campestris pv. phaseoli indicating that the techniques could be used for the specific detection of the two diseases. Epidemiological studies showed that common blight was more prevalent in summer and halo blight in winter. Both diseases were observed to evolve rapidly in field plot trials in the susceptible variety V 5003. Common blight increased from 3 to 55 per cent in one month while halo blight incidence rose from 5 per cent to 45 per cent in six weeks. In yield assessment trials, common blight induced losses of 14 per cent whereas halo blight caused a reduction by as much as 75 per cent. Testing of the efficacy of copper oxychloride in vitro, by the incorporation of the bactericide in nutrient agar, showed that it was effective against halo, common and fuscous blight pathogens at 35, 45 and 35 ppm respectively. Using the inhibition zone method in nutrient agar for the antibiotic streptomycin, susceptibility occurred at 200, 250 and 250 ppm for Pseudomonas savastanoi pv. phaseolicola, Xanthomonas campestris pv. phaseoli, and Xanthomonas campestris pv. phaseoli var. fuscans respectively. As bacterial blights were a major constraint in seed production, a four-step procedure was devised for the creation of a nuclear stock of planting material. Seeds were disinfected and placed on agar. Infected ones were discarded and uncontaminated ones transferred to an insect-proof greenhouse for the first multiplication. After a second bulking under the same conditions, the seed was planted in the field with a wide spacing between plants under drip-irrigation. Overhead irrigation and rainfed conditions were inappropriate for seed production. Despite that field infection by bacterial blights occurred, this scheme is promising for seed production in Mauritius. The use of seed treatments, protective sprays and diagnostic techniques in seed production are discussed. | |
| Bacterial diseases Seed-borne diseases Pathogens Beans (Phaseolus) Phaseolus vulgaris Common blight Fuscous blight Halo blight Brown spot Serology Epidemiology Seeds | |
| Mauritius | |
| Beans (Phaseolus) | |
| Diseases - Bacterial diseases | |
| 2000-03-14 | |
| En | |
| Path | |
| Cat | |
| PATH |