Submitted to: Seed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/1996
Publication Date: N/A
Interpretive Summary: A simple, reliable technique to test for the pathogenicity of Xanthomonas oryzae pv. oryzae was developed. A plastic disposable 1.0-ml syringe was modified by attaching a rubber ring to the blunt end of the syringe. Using an inoculum containing 10**6-7 cfu viable cells of the pathogen, the bacteria were infiltrated into the leaf with the syringe. After 10-14 days in a lighted dew chamber, dark green water-soaked lesions resulted. In contrast, when the standard leaf clipping method was used only bleached or tan-colored lesions developed. The method should be useful as a rapid reliable method for testing for pathogenicity and breeding for resistance.
Technical Abstract: Pathogenicity testing of Xanthomonas oryzae pv. oryzae by the standard leaf clipping technique resulted in a bleached, hypersensitive-like reaction preceding a general yellowing or browning of the tissue. Water-soaked lesions were never observed and the pathogen could not be isolated. Using a plastic disposable 1.0-ml syringe modified to infiltrate rice leaves, water-soaked lesions developed in leaves of 4- to 5-leaf stage plants growing in a lighted dew chamber, 10-14 days after infiltration with an inoculum containing 10**6-7 cfu X. o. pv. oryzae/ml. Exudate was often evident. The newly developed infiltration technique was to compare the standard leaf clipping technique by inoculating plants of rice cv IR-24 with three strains of X. o. pv. oryzae from China, three strains of X. o. pv. oryzae (X1-5, X1-8, and X37-2) from Texas, two strains of X. o. pv. oryzicola from China, and two unknown yellow- pigmented bacteria isolated from California rice seeds in a commercial, lighted dew chamber. Inoculation by the clipping technique usually resulted in bleached or tan-colored lesions regardless of the organism used. Using the infiltration technique, dark green water-soaked lesions consistently developed with all strains of X. o. pv. oryzae and X. o. pv. oryzicola from China, but not with the Texas strains or the unknown bacteria