Ecological factors affecting the distribution of pseudomonas solanacearum in Kenya

Abstract

One hundred and thirty-eight potato farms were examined for the presence of bacterial wilt in Central,Eastern and Rift Valley Provinces. The altitude of these areas ranged from 1390 m to 2790 m above the sea level and the mean annual o temperatures ranged from 12.1 C to 21.2oC. Twenty-one per cent of the farms were found infested with bacterial wilt. The highest percentage of infested farms lay between an altitude of 1520 m and 2120 m. The disease incidences decreased with elevations outside this zone. Disease symptoms were used to identify diseased plants in the field. Thirty-three isolates collected were classified as Pseudomonas solanacearum biochemical type II or race 3 of Buddenhagen, et ale (1962). Potatoes (Solanum tuberosum) were infected exclusively by this biochemical type. Biochemical type III was isolated from egg-plant (s. melongena). This biotype was not isolated from potataes and was not found pathogenic to potatoes. The optimum growth temperature of f. solanacearum in The minimum and maximum temperatures were around 13°C and 35°C respectively. No growth was obtained at 12°C and 37°C. The in vivo growth-chamber inoculation experiments showed an increase in the rate of wilt development as temperatures increased from 14°C to 24°C. At higher temperatures, the rate of wilt development decreased. Dose xiv response experiments in the greenhouse during four seasons of the year showed that the concentration of viable cells required for 50% of inoculated plants to wilt decreased with o 0 an increase in temperature from 16.9 C to 20.7 C. The pathogen survived best in soil at 24°C followed o 0 l by 20 C and then 18 C. At these temperatures the bacteria multiplied, reached a peak in the 14th day, then declined slightly. The bacterial population remained almost constant for 28 days at 14°C while at 28,30 and 33°C, the concentrations of bacteria declined. Most plants in0culated with the pathogen at high altitude had latent infection. When tubers from these plants were kept in humid conditions at 30oC, 20% showed disease symptoms. .E. 80lanacearum was isolated from 3% of externally symptomless tubers and 14.9% of plants raised from symptomless tubers developed wilt symptoms under favourable conditions. P. solanacearum is a good immunogen. Antisera pr-epar-ed against the bacterium had titres ranging from 1/128 to 1/1024. The antisera were found to be specific and could be used in the laboratory for quick identification of E. solanacearum.