Production of Phytohormones by Pseudomonas amygdali and their Role in the Hyperplastic Bacterial Canker of Almond

Abstract

Abstract The cytokinin and auxin production by Pseudomonas amygdali was studied in relation to bacterial virulence on almond plants. All isolates of Pseudomonas amygdali used in this study secreted indoles and cytokinins in culture medium although their relative amount varied among the strains. t‐zeatin (t‐Z) and indole‐3‐acetic acid (IAA), which proved to be the main componenets of cytokinin and indole mixtures, ranged respectively, as determined by HPLC, from 0.013 to 4.621 mgl,−1 and from 0.1 to 15.14 mg l−1.The production of IAA and t‐Z appeared to be correlated to virulence of P. amygdali. The highly virulent strains, having the shortest incubation period and inducing the longest cankers produced high levels of IAA and t‐Z in vitro. On the other hand, the weakly virulent strains, having longer incubation periods and inducing shorter cankers, secreted low levels of IAA and t‐Z. Strain A142, producing high level of IAA and low level of t‐Z had the same incubation, period as the highly virulent strains but a canker similar to that of the other weakly virulent strains.These results suggest that in the disease process by P. amygdali on almond the amount of IAA and cytokinins are correlated respectively to the length of the incubation period and to the final length of the cankers.