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Youjian Lin, R.H. Brlansky, and Charles A. Powell

Six severe and six mild Florida isolates of citrus tristeza virus (CTV) were used to evaluate the transmission efficiency of the virus from grapefruit seedlings by single brown citrus aphids (Toxoptera citricida Kirkaldy) (BrCA) from colonies initiated by aphids obtained from citrus groves in Fort Pierce, Fla. The transmission rate to 2120 receptor plants [`Mexican' lime (Citrus aurantifolia)] from grapefruit by single BrCA was 1.5%. Single BrCA transmitted four of the six severe isolates and three of the six mild isolates of CTV. The average transmission rate of severe isolates was 1.8%, higher than that (0.9%) of mild isolates. Severe isolate Y-7 had the highest transmission rate among six severe isolates, 3.6%. Mild isolate Y-23 had the highest transmission rate among the mild isolates, 3.0%. The transmission rates of CTV by alatae, apterae, or nymphs of BrCA were 1.5%, 1.5%, and 1.0%, respectively. The results suggested that BrCA is an inefficient vector of CTV when the source plant is grapefruit.

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Charles A. Powell and Youjian Lin

One hundred single brown citrus aphid (BCA) (Toxoptera citricida Kirkaldy) transmission attempts were made from each of 16 different citrus trees [8 grapefruit (Citrus paradisi Macf.) and 8 sweet orange (C. sinensis (L.) Osbeck)] previously inoculated with decline-inducing (T36-CTV), non-decline-inducing (T30-CTV), a mixture of the two Citrus tristeza virus isolate types, or no CTV. Successful CTV transmission occurred in 1.5% of attempts from grapefruit trees that had been bark-chip-inoculated with T36-CTV, 3% of attempts from orange trees inoculated with T36-CTV, 3% of attempts from grapefruit trees inoculated with both T36- and T30-CTV, 4% of attempts from orange trees inoculated with both T36- and T30-CTV, 1.5% of attempts from grapefruit trees inoculated with T30-CTV, and 3.5% of attempts from orange trees inoculated with T30-CTV. Single BCA were able to recover T30-like-CTV from trees believed to be inoculated only with T36-CTV, and T36-like-CTV from trees believed to be inoculated only with T30-CTV, suggesting that these inoculum sources were also mixtures of T36-CTV and T30-CTV. The T36-CTV was not immunologically detectable in some of the trees from which it was transmitted indicating that single BrCA can recover T36-CTV from a T36-CTV/T30-CTV mixture in which the T36-CTV is an undetectable, minority component.

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Charles A. Powell, Mark A. Ritenour, and Robert C. Bullock

citrus aphid ( Toxoptera citricida Kirkaldy) that transmits citrus tristeza virus ( Roistacher and Bar-Joseph, 1987 ), the Asian citrus psyllid ( Diaphorina citri Kuwayama) that transmits Candidatus Liberibacter asiaticas and C. L. americanum, causal

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David G. Hall and L.G. Albrigo

(L.)] and blue green weevil [ Pachnaeus litus (Germar)] ( Futch and McCoy, 1994 ) and by aphids such as spirea aphid ( Aphis spireacola Patch) and brown citrus aphid [ Toxoptera citricida (Kirkaldy)] ( Browning et al., 1995 ). Infections of citrus

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William S. Castle

citrus aphid, Toxoptera citricida (Kirkaldy), in 1995. Growers need information about alternative rootstocks to replace sour orange. Attempts to discover other rootstocks with qualities equal or sufficiently similar to those of sour orange have not been