Etiology of Pseudomonas syringae pv. sesami causing leaf spot of sesame and approach to its control measure
1994
Petcharat Yowabut
Morphological, physiological and biochemical characteristics of the causal bacterium isolated from infected sesame in Thailand were studied and compared to Pseudomonas syringae pv. sesami from DSIR Plant Protection, New Zealand. All 5-Thai strains were pathogenic on inoculated sesame which other bacteriological characteristics were not taxonomic difference from the reference strains. The results of those studies confirmed that the causal bacterium of sesame leaf spot in Thailand was Ps. syringae pv. sesami Malkoff (1930). Comparison of disease severity and yield of 14 sesame varieties revealed that Col 55 was resistant; Dam Dang-Phitsanulok, Col 30/nw-3, Nakornsawan, Buriram and Roi-et 1 were susceptible and the rests were intermediate. The susceptible varieties were 86.86 percent higher in disease severity, 7.38 percent smaller in seed weight, and 37.58 percent lower in seed yield than resistant variety. All seeds of 14 varieties harvested from diseased sesames were found to be seedborned incidence with the infected seed percentage of 62.13 in average and the causal bacteria were found only at seed coat of 100 percent without at embryo and endosperm. Disease control through hot water (55 deg C) and chemical (75 ppm streptomycin) seed treatment at 30 min each, gave the best results of 47.25 and 100 percent disease reduction with 84.4 and 88.6 percent seed germination, respectively. In the field experiment, 250 ppm streptomycin showed the best results when sprayed 10 times at 7-day interval starting 7 days after sesame emerged giving yield of 104.5 kg/rai compared with untreated control of 28.7 kg/rai in average of 2-crop season trials.
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