Elicitin genes expressed in vitro by certain tobacco isolates of Phytophthora parasitica are down regulated during compatible interactions.

Phytophthora spp. secrete proteins called elicitins in vitro that can specifically induce hypersensitive response and systemic acquired resistance in tobacco. In Phytophthora parasitica, the causal agent of black shank, most isolates virulent on tobacco are unable to produce elicitins in vitro. Recently, however, a few elicitin-producing P. parasitica strains virulent on tobacco have been isolated. We investigated the potential diversity of elicitin genes in P. parasitica isolates belonging to different genotypes and with various virulence levels toward tobacco as well as elicitin expression pattern in vitro and in planta. Although elicitins are encoded by a multigene family, parAl is the main elicitin gene expressed. This gene is highly conserved among isolates, regardless of the elicitin production and virulence levels toward tobacco. Moreover, we show that elicitin-producing P. parasitica isolates virulent on tobacco down regulate parAl expression during compatible interactions, whichever host plant is tested. Conversely, one elicitin-producing P. parasitica isolate that is pathogenic on tomato and avirulent on tobacco still expresses parAl in the compatible interaction. Therefore, some P. parasitica isolates may evade tobacco recognition by down regulating parA1 in planta. The in planta down regulation of parA1 may constitute a suitable mechanism for P. parasitica to infect tobacco without deleterious consequences for the pathogen.

Diversity of Virulence in Phytophthora parasitica on Tobacco, as Reflected by Nuclear RFLPs.

ABSTRACT A worldwide collection of P. parasitica isolates was investigated for the ability to infect tobacco and tomato, as related to elicitin production. Elicitin was produced by all nontobacco isolates, and nonproducing strains all were isolated from tobacco. In addition, producing strains were isolated from tobacco and coexisted with nonproducing (TE ) strains. Elicitin production generally was associated with low virulence on tobacco and frequent pathogenicity on tomato, whereas TE isolates generally were highly virulent and specialized to tobacco. Analysis of both mitochondrial and nuclear DNA restriction fragment length polymorphisms indicated, for the first time, that black shank isolates can be distinguished from other P. parasitica isolates on the basis of genetic criteria. Our results suggest that severe black shank is caused by a limited number of TE strains that have been disseminated by clonal evolution. Mutations in the TE phenotype seem to have arisen independently in several genetic backgrounds and distinct geographic areas. The fortuitous absence of elicitin production has precluded population replacements in areas of intensive tobacco cultivation. Thus, monitoring the loss of elicitin production in developing tobacco areas should be considered in disease management.

[Parotiditis in postvaccination period. Epidemiologic pattern and vaccine effectiveness in an epidemic outbreak]. / La parotiditis en época posvacunal. Patrón epidemiológico y efectividad vacunal en un brote epidémico.

BACKGROUND: Upon the detection of an excess number of cases of parotiditis in La Almolda (Zaragoza) a descriptive study of the epidemic was carried out with vaccination efficacy being quantified. METHODS: The definition and system of detection of the cases was established. To calculate the rate of infection the available demographic data were used as denominators. A study of retrospective groups was designed to calculate the vaccination efficacy including one group of vaccinated subjects and another of non vaccinated subjects. Age and viral contact were considered as inclusion criteria. RESULTS: Fifty-two cases of parotiditis were detected. The rate of infection in a population of under 30 years of age was 18.9%. The most affected age group corresponded to the interval of between 10-14 years of age with a specific rate of 46.5%. The risk of infection was greatest amongst public school students (RR = 5; p = 0.00015). Vaccination efficacy was 74.68%. CONCLUSIONS: This study confirms the tendency that parotiditis affects older subjects during the prevaccination period. The vaccination efficacy found to be 74.68% was lower the efficacy determined from seroconversion studies.