Melon and watermelon bacterial fruit blotch, incited by Acidovorax citrulli, is limited to some areas in Brazil but causes important losses, mainly in melon-producing regions. Although genetic diversity has been observed among strains belonging to the species, they are considered a homogeneous group based on the fact that they show only slight physiological or nutritional differences. The objective of this study was to compare Brazilian strains from melon and watermelon by means of biochemical, pathogenicity, serological and molecular assays. Fifteen biochemical tests, cross inoculation between strains and hosts, ELISA and repetitive sequence analysis (rep-PCR) with the primers REP, ERIC and BOX were conducted. No differences were revealed by nutritional characterization or serology, but cross inoculation showed different pathogenicity groups, which could explain high aggressiveness of the bacteria to melon crops in some regions. Molecular analysis by BOX-PCR clustered strains according to their geographical origin, while ERIC-and REP-PCR, analyzed together, indicated genetic diversity, but without geographical or host origin relationships. One test that could be used to verify the pathogenicity of strains by inoculating detached leaf petioles, showing results in 36 h, is proposed here.

RESUMOEm um plantio comercial localizado no Vale do Ribeira, no estado de São Paulo, foram observadas plantas de abobrinha-de-moita (Cucurbita pepo L.) apresentando superbrotamento de ramos, malformação da parte aérea e folhas disformes e enrugadas. Através de PCR foi demonstrada a presença de fitoplasma associado aos tecidos doentes. Um fitoplasma do grupo 16SrIII foi identificado por PCR e pela análise de RFLP, conduzida com cinco enzimas de restrição. A presente comunicação se constitui no primeiro relato da presença de um fitoplasma do grupo 16SrIII em abobrinha-de-moita no Brasil. Palavras-chaves: Mollicutes, Cucurbitaceae, Cucurbita pepo, RFLP. ABSTRACT Summer squash: a new host of phytoplasm belonging to the 16SrIII groupIn a commercial field located in the Vale do Ribeira, in the State of São Paulo, Brazil, plants of summer squash (Cucurbita pepo L.) exhibiting witches' broom and leaf deformation were observed. PCR assays demonstrated the presence of phytoplasma associated with diseased tissues. A phytoplasma belonging to the 16SrIII group was identified by PCR and RFLP analysis performed with five restriction enzymes. The present note is the first report of the presence of phytoplasma representative of the 16SrIII group in summer squash in Brazil.