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Survival of Pseudomonas solanacearum EF. Smith in the Rhizosphere of Some Weed and Economic Plant Species.
Thesis Abstract:
Kelman's Karganilla and Buddenhagen's, Nesmith and Jenkins', and Harris' media were studied for their selectivity and efficiency in recovering P. solanacearum from soils. Results indicated taht Nesmith and Jenkins' medium was the most suited for quantitative assay of the pathogen in some Philippine soils.
Nesmith and Jenkins' medium was used to monitor population changes of P. solanacearum in naturally infested soils planted to several plant species commonly assoiciated with tomato cultivation in the Philippines, either as a weed or as a rotation crop. Before introduction of the test plants, the initial population of P. solanacearum in ther infested soils was not significantly different from each other. When rhizosphere and non-rhizosphere soils of the plants were sampled at weekly intervals, a gradual decline in the population of the pathogen was observed in both types of soil, excet in Portulaca oleracea (common purslane) which showed a gradual but distinct population increase in the rhizosphere soil. Population decline of the bacterium was lowest with P. oleracea. Echinochloa colona (Jungle rice), Amaranthus spinosus (spiny amarantha), Phaseolus aureus (mungbean) and Eleusine indica (goose grass), while rice and corn showed relatively greater suppression of the pathogen. Latent infection ws found in P. oleracea through isolations, but not in the other test plant
Pathogen population was also higher in the rhizosphere than in the non-rhizosphere soil of the weed plants and mungbean. On the other hand, both rice and corn had higher population of the bacterium in non-rhizosphere than in rhizosphere soil. In bare fallow soil, population decline was as slow as that
Bioassay of the soil with-susceptible "Yellow Plum" tomato seedlings gave varying results, depending on the plant that had been growing in the soil. Soil with common purslane exhibited the highest level of wilting, while those planted to rice and corn had the lowest incidence of wilting. Compared to the bare fallow soil, soils planted to goose grass, jungle rice and purslane showed non-significant differences, but those planted to rice, corn and spiny amaranth had significant differences.
Results of the study indicate, therefore, that in the absence of host plants, these common weeds in tomato-growing areas contribute to the survival of P.solanacearum in the soil. Control of these weeds could possibly lower bacterial wilt incidence, while rotation of susceptible crops with either rice or corn would help considerably in reducing the wilt problem.