Author : Pisan Sirithorn

Summary : Ten isolates of the rambutan vein necrosis bacterium (RVNB) collected from Laguna and Oriental Mindoro, Philippines were evaluated for their bacteriological and pathological characteristics. Findings revealed that no distinct differences existed among isolates. The RVNB was Gram-negative, rod-shaped and motile with a single polar flagellum. Cell size was 0.58 u by 1.5 u. Agar colonies were shiny, mucoid, convex with entire margin and white in nutrient agar and peptone sucrose agar but yellow on yeast extract dextrose calcium carbonate agar. No flourescent pigment was present in any of the isolates on King's medium B agar. Oxidative but not fermentive reaction was observed on glucose medium. All isolates were negative in the test on oxidase, methyl red, Voges-Proskauer, indole production, urease, and nitrate reduction, but positive for hydrogen sulfide production, aesculin, and starch hydrolysis tests. Gelatin was liquefied weakly or negatively and marked pretolysis occurred in litmus milk test. The bacterium produced acid in L-arabinose, cellobiose, galactose, glucose and mannose but not in trehalose. In salt, tolerance was 3-4 percent sodium chloride (NaCL). A pathogenicity test showed that seven field crops and two fruit crops from five families tested, RVNB incited the disease only in rambutan. The first visible symptom of the disease was noted two weeks after inoculation and typical vein necrosis after four weeks. Based onits morphological, biochemical, and pathological characters and in accordance with the new nomenclature, the RVNB is designated as Xanthomonas campestris pv. nepheliaelappaceae to be included in the non-pigmented group because it can infect only Nephalium lappaceum L. It failed to infect the other test plants. Results of the study suggested that there existed no danger in intercropping field crops with rambutan.