The potential role in pathogenicity of extracellular products (ECP) of the fish pathogen Aeromonas salmonicida was investigated. Evidence is presented that determinants of host damage are produced extracellularly by A. salmonicida. In vitro, the bacterium produced a number of extracellular enzymic and ctyolytic activities, including proteases and an heterogeneous haemolysin which was active against rainbow trout erythrocytes. Solubilization of trout erythrocytes in vitro resulted from the cooperative effects of the haemolysin and a caseinolytic protease. The caseinolytic protease was implicated in host damage; the in vivo effects of the caseinase may have been potentiated by haemolysin. The production of extracellular proteolytic and haemolytic activities by a number of isolates of A. salmonicida was studied; some potentially important differences between isolates were found. Evidence is presented that rainbow trout possess humoral mechanisms of resisting the toxic products of A. salmonicida. Proteolytic and haemolytic activities of ECP were inhibited, and the in vivo toxicity of ECP was neutralized, by normal trout serum. In vitro, factors in normal trout serum appearaed to form soluble complexes, as well as insoluble precipitates, with component(s) of ECP. In vitro, ECP caused a reduction in circulating levels of an alpha-2 macroglobulin analogue in rainbow trout. As putative determinants of pathogenicity, extracellular factors of A. salmonicida are potentially important in conferring protective immunity against furunculosis. The humoral immune response of rainbow trout and rabbits to components of ECP was investigated. At least 15 components of ECP, including the caseinase and haemolysin, were immunogenic in the rabbit. In the trout, antibodies to only 4 components of ECP were detected and no antibody to the caseinase or haemolysin was found. It is suggested that the effectiveness of furunculosis vaccines might be improved if the immunogenicity in trout of certain ECP components could be enhanced.

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O cancro cítrico, causado por Xanthomonas axonopodis pv. citri (Xac), é um dos mais graves problemas fitossanitário da citricultura brasileira. Com a introdução da lagarta minadora dos citros (Phyllocnistis citrella [LMC]), houve um aumento drástico do número de focos do cancro cítrico, além da mudança do padrão espacial de fortemente agregado para moderadamente agregado e ao acaso. Foram avaliados: (1) suscetibilidade de três condições foliares: folha intacta, ferimento mecânico e injúria de LMC nas fases ovo, 1º ínstar, 3º ínstar e pupa, inoculados em diferentes concentrações de Xac (101, 102, 104 e 106 ufc/ml); (2) período de suscetibilidade da folha intacta, do ferimento mecânico e injúria de LMC inoculados a 106 ufc/ml; e (3) efeito da temperatura (12, 15, 20, 25, 30, 35, 40 e 42°C) e duração do molhamento foliar (0, 4, 8, 12, 16, 20 e 24 h) em folhas sem ferimento inoculadas a 106 ufc/ml. A concentração mínima de inóculo para causar sintomas da doença em folha intacta, injúria de LMC fase ovo e 1º ínstar foi de 104 ufc/ml; em ferimento mecânico e injúria de LMC fase 3º ínstar e pupa, 102 ufc/ml. Injúria da fase pupa resultou em grande severidade do que nos demais tratamentos a 106 ufc/ml (2 vezes maior do que em folha intacta).O período de suscetibilidade da injúria de LMC foi seis vezes mais longo do que do ferimento mecânico e a máxima suscetibilidade foi três vezes maior que em folha intacta. A LMC está relacionada com o aumento do dano que expõem mesofilo foliar à infecção direta de Xac, aumentando a suscetibilidade da folha por longo período. A faixa de temperatura ótima para o desenvolvimento do cancro cítrico foi de 25-35ºC. Entretanto, a severidade foi mais alta entre 30-35ºC. Sintomas de cancro não desenvolveram a 42ºC e na ausência de molhamento foliar. O efeito da temperatura foi maior do que a duração do molhamento foliar. A mínima duração de molhamento para infecção de Xac foi menor que 4 horas. / Asiatic citrus canker, caused by X. axonopodispv.citri (Xac), is one of the most serious phytosanitary problems in Brazilian citrus crops.The introduction of the citrus leafminer (Phyllocnistis citrella [CLM]), has resulted in an increase in the number of disease foci and has changed the spatial pattern of citrus canker symptomatic trees from strong aggregation to intermediate aggregation and random patterns. We evaluated: (1) susceptibility of three distinct leaf condition: intact leaves, mechanical wounding, and injury caused by CLM at the egg stage, 1st instar, 3rd instar, and pupal stage, inoculated at different concentration of Xac (101, 102, 104, and 106 cfu/ml); (2) susceptibility period of intact leaves, mechanical wounding, and CLM injury inoculated at 106 ufc/ml; and (3) effect of temperature (12, 15, 20, 25, 30, 35, 40 and 42°C) and leaf wetness durations (0, 4, 8, 12, 16, 20, and 24 h) on unwounded leaves inoculated at 106 ufc/ml. The minimum inoculum concentration to cause symptom development in intact leaves, CLM injury at the egg stage and 1st instar was 104 cfu/ml; in mechanically wounded leaves and CLM injuries at the 3rd instar and pupa stage, 102 cfu/ml. The injuries from pupa stage resulted in greater disease severity than other treatments at 106 cfu/ml (two times higher than in the intact leaf). Susceptibility period of CLM injury was six time longer than mechanical wounding and maximum observed susceptibility was three times higher than intact leaf. CLM is related to the amount of damage that exposes mesophyll cells to direct Xac infection, increasing the susceptibility of leaf for long period. Optimal temperature for development of citrus canker was 25-35°C. However, disease severity was highest in the range 30-35°C. Symptoms did not develop at 42°C and zero hour of leaf wetness duration. Effect of temperature was .greater than leaf wetness duration. The minimum wetness duration for Xac infection was as short as 4 h.

O cancro cítrico, causado por Xanthomonas axonopodis pv. citri (Xac), é um dos mais graves problemas fitossanitário da citricultura brasileira. Com a introdução da lagarta minadora dos citros (Phyllocnistis citrella [LMC]), houve um aumento drástico do número de focos do cancro cítrico, além da mudança do padrão espacial de fortemente agregado para moderadamente agregado e ao acaso. Foram avaliados: (1) suscetibilidade de três condições foliares: folha intacta, ferimento mecânico e injúria de LMC nas fases ovo, 1º ínstar, 3º ínstar e pupa, inoculados em diferentes concentrações de Xac (101, 102, 104 e 106 ufc/ml); (2) período de suscetibilidade da folha intacta, do ferimento mecânico e injúria de LMC inoculados a 106 ufc/ml; e (3) efeito da temperatura (12, 15, 20, 25, 30, 35, 40 e 42°C) e duração do molhamento foliar (0, 4, 8, 12, 16, 20 e 24 h) em folhas sem ferimento inoculadas a 106 ufc/ml. A concentração mínima de inóculo para causar sintomas da doença em folha intacta, injúria de LMC fase ovo e 1º ínstar foi de 104 ufc/ml; em ferimento mecânico e injúria de LMC fase 3º ínstar e pupa, 102 ufc/ml. Injúria da fase pupa resultou em grande severidade do que nos demais tratamentos a 106 ufc/ml (2 vezes maior do que em folha intacta).O período de suscetibilidade da injúria de LMC foi seis vezes mais longo do que do ferimento mecânico e a máxima suscetibilidade foi três vezes maior que em folha intacta. A LMC está relacionada com o aumento do dano que expõem mesofilo foliar à infecção direta de Xac, aumentando a suscetibilidade da folha por longo período. A faixa de temperatura ótima para o desenvolvimento do cancro cítrico foi de 25-35ºC. Entretanto, a severidade foi mais alta entre 30-35ºC. Sintomas de cancro não desenvolveram a 42ºC e na ausência de molhamento foliar. O efeito da temperatura foi maior do que a duração do molhamento foliar. A mínima duração de molhamento para infecção de Xac foi menor que 4 horas. / Asiatic citrus canker, caused by X. axonopodispv.citri (Xac), is one of the most serious phytosanitary problems in Brazilian citrus crops.The introduction of the citrus leafminer (Phyllocnistis citrella [CLM]), has resulted in an increase in the number of disease foci and has changed the spatial pattern of citrus canker symptomatic trees from strong aggregation to intermediate aggregation and random patterns. We evaluated: (1) susceptibility of three distinct leaf condition: intact leaves, mechanical wounding, and injury caused by CLM at the egg stage, 1st instar, 3rd instar, and pupal stage, inoculated at different concentration of Xac (101, 102, 104, and 106 cfu/ml); (2) susceptibility period of intact leaves, mechanical wounding, and CLM injury inoculated at 106 ufc/ml; and (3) effect of temperature (12, 15, 20, 25, 30, 35, 40 and 42°C) and leaf wetness durations (0, 4, 8, 12, 16, 20, and 24 h) on unwounded leaves inoculated at 106 ufc/ml. The minimum inoculum concentration to cause symptom development in intact leaves, CLM injury at the egg stage and 1st instar was 104 cfu/ml; in mechanically wounded leaves and CLM injuries at the 3rd instar and pupa stage, 102 cfu/ml. The injuries from pupa stage resulted in greater disease severity than other treatments at 106 cfu/ml (two times higher than in the intact leaf). Susceptibility period of CLM injury was six time longer than mechanical wounding and maximum observed susceptibility was three times higher than intact leaf. CLM is related to the amount of damage that exposes mesophyll cells to direct Xac infection, increasing the susceptibility of leaf for long period. Optimal temperature for development of citrus canker was 25–35°C. However, disease severity was highest in the range 30–35°C. Symptoms did not develop at 42°C and zero hour of leaf wetness duration. Effect of temperature was .greater than leaf wetness duration. The minimum wetness duration for Xac infection was as short as 4 h.