Variation in the Virulence of Xanthomonas oryzae (3)

Interaction Between Avirulent Mutants and Virulent Wild Type Isolates

Abstract

Avirulent mutants of Xanthomonas oryzae occur during the course of successive culture on artificial media, and the population of these mutants gradually increases. In this experiment, mutual interference in multiplication between avirulent mutant (Av) and virulent wild type (V) in liquid media or inoculated rice leaves was studied. For the purpose of these studies, streptomycin resistant mutant from Av (Av-R), and that from V (V-R) were used frequently. Between Av and Av-R or between V and V-R, no difference could be found in virulence, colony morphology, lysotype, and bacterial physiology, except streptomycin resistance. Multiplication of V-R in liquid medium was markedly depressed by adding nearly the equal amount of Av. When V-R was mixed with Av and inoculated to rice leaves, lesion enlargement was inhibited in proportion to the amount of Av added. Multiplication of V-R in rice leaves was also inhibited by the addition of Av. Multiplication of Av-R in liquid medium was influenced very little by adding V. When Av-R was inoculated singly, it multiplied during 10-15 days within 2-3cm distance around the inoculated points, though no visible lesion was formed on the leaf. By mix-inoculation with Av-R+V, bacterial population of Av-R in leaves was much increased, and at the same time, Av-R was distributed within wider area in leaves.