Pierce's disease investigations

Comparative Dispersal ofHomalodisca coagulataandHomalodisca liturata(Homoptera: Cicadellidae)

“…Of the various environmental factors that might inßuence sharpshooter dispersal, we found that in the open setting of an abandoned alfalfa Þeld, wind speed was the only environmental parameter that explained Winkler et al (1949) noted that for the green sharpshooter, Draeculacephala minerva Ball, ßight was inhibited by high winds, but made no mention of the wind speed that inhibited ßight. We found that glassy-winged and smoke tree sharpshooters rarely initiated ßights when the average wind speed exceeded 3 m s Ϫ1 .…”

Habitats and dispersal of the principal leafhopper vectors of Pierce's Disease in the San Joaquin Valley

“…Irrigated pastures, bogs, stream banks, or locations with a luxuriant but not dense growth of grasses were favored breeding habitats. This leafhopper was collected regularly from weedy stands of alfalfa and from weeds in vineyards (Winkler et al 1949). On the basis of its abundance and widespread distribution, the green sharpshooter was considered to be the most important vector of Pierce's disease bacterium in central California (Winkler et al 1949).…”

“…The pattern of occurrence of PD suggests that insect vectors were responsible for its natural spread (Hewitt et al 1946), and xylem-feeding leafhoppers of the subfamily Cicadellinae (= Tettigellinae), commonly known as sharpshooters, were found to be capable of transmitting the causal agent of the disease (Frazier 1943;Hewitt et al 1942Hewitt et al , 1946. In the Central Valley of California two sharpshooter species, the green sharpshooter Draeculacephala minerva (Ball) and the redheaded sharpshooter Draeculacephala fulgida (Nottingham), are considered the most important PD vectors because of their abundance relative to other xylem-feeding species (Hewitt et al 1942;Winkler et al 1949). In coastal California grape-growing regions, the blue-green sharpshooter Graphocephala atropunctata Signoret (= Hordnia circellata) is the principal PD vector (Hewitt et al 1942;Purcell 1975 ).…”

“…Neither D. minerva nor C. fulgida, however, was ever found frequently on grape. Grape apparently was only an occasional or "accidental" host plant (Winkler et al 1949) that, nonetheless, could be infected after exposure to infective individuals of either species (Frazier 1943;Severin 1949). Sharpshooter dispersal, therefore, is important in the spread of PD.…”

Isolamento, caracterização genética por RAPD e resistência a antibióticos em <i>Xylella fastidiosa</i>

“…A primeira doença causada por X fastidiosa a ser relatada foi a de Pierce ('Pierce's Disease -PD) em videira na California, EUA, no final do século XIX (Pierce, 1982). Durante oitenta anos acreditou-se que o patógeno era de origem viral, por suas características de transmissão, uma vez que é transmitido por enxertia e insetos vetores, além dos sintomas de necrose marginal em folhas (Winkler, 1949). Posteriormente, a bactéria foi visualizada através de microscopia nos vasos do xilema de plantas sintomáticas (Hopkins & Mollenhauer, 1973).…”