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Role of Flagellar Motility in the Invasion of Bean Leaves by Pseudomonas phaseolicola. N. J. Panopoulos, Assistant Research Plant Pathologist, Department of Plant Pathology, University of California, Berkeley 94720; M. N. Schroth, Professor, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 64:1389-1397. Accepted for publication 8 May 1974. DOI: 10.1094/Phyto-64-1389.

The role of flagellar motility in the invasion of bean leaves by Pseudomonas phaseolicola was examined using isogenic pairs of motile and nonmotile mutants. The latter possessed paralysed flagella and did not spread in semisolid medium. They consisted of predominantly nonmotile cells, but contained a few motile individuals presumably because of leakiness of their mutations. Spontaneous motile revertants were obtained and used in comparative inoculation tests. With externally applied inocula, motile strains caused up to 12 times as many lesions than did nonmotile counterparts. Similar results were obtained with wounded and nonwounded leaves. Invasion of water-congested leaves by motile or nonmotile strains was 90 to 400 times greater than of noncongested leaves. Systemic invasion in the plant was not related to motility. When leaves were immersed in motile bacterial suspensions containing 106 cells/ml, the initial rates of entry under optimal conditions were 180 to 620 cells/min/cm2 of leaf tissue. Invasion rates calculated from the gas effusion equation were in good agreement with experimentally measured rates for nonchemotactic organisms, but were somewhat lower for chemotactic P. phaseolicola. Also, the long-term distribution of bacteria between inside and outside congested leaf tissue deviated substantially upwards from that predicted for a simple diffusional equilibrium, suggesting that the bacteria were attracted to and concentrated in the leaf tissue.

Additional keywords: paralysed mutants, water congestion, chemotaxis, effusion model.