Association of double‐stranded RNA with whitefly‐mediated silvering in squash

Abstract

A disorder of unknown aetiology appearing as silvering on squash (Cucurbita pepo) leaves has become prevalent in south Florida. Typical symptoms, observed after 2 weeks of exposure to adults of Bemisia tabaci, the sweet potato whitefly (SPWF) include vein clearing followed by silvering of whole leaves. Fruits from affected plants are blanched or streaked longitudinally. The silverleaf syndrome was not mechanically transmissible when crude extracts of symptomatic leaves were used as inoculum. Two sizes of double‐stranded RNA (dsRNA) of c. 4.6 and 4.2 kilobase pairs (kbp) were consistently observed in leaf extracts of caged, whitefly‐infested, symptomatic plants. In contrast, caged plants not exposed to whiteflies showed no symptoms and contained no detectable dsRN A. In addition, squash plants exposed to SPWF colonies from California neither developed silverleaf symptoms nor contained any dsRNA. Double‐stranded RNA could also be readily detected in whitefly‐infested yellow summer squash and zucchini from the field. However, asymptomatic eggplant and watermelon infested with SPWF from nearby fields did not contain detectable dsRNA. Dot‐spot hybridization assays using an RNA‐specific probe detected homologous sequences in both adults and nymphs of SPWF that induced silverleaf symptoms but not in adults and nymphs of SPWF that could not induce silverleaf symptoms. These results, along with the non‐endogenous nature of the detected dsRNA suggest that the dsRNA is or is associated with the causal agent of whitefly‐mediated leaf silvering in squash.

Characterization and distribution of esterase electromorphs in the whitefly,Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae)

“…The other was termed the B biotype, or the poinsettia strain. The B biotype is more fecund than the A, produces greater amounts of honeydew, has a broader host plant range, exhibits significantly higher levels of insecticide resistance, induces several different phytotoxic disorders in certain plant hosts (Anthony et al, 1995;Bethke et al, 1991;Bharathan et al, 1990;Byrne and Miller, 1990;Cohen et aL, 1992;Brown, 1991, 1993;Liu et aL, 1992), and has recently been proposed as a new species, Bemisia argentifolii (Bellows et aL, 1994;Perring et al, 1992).…”

Variation in biological characteristics and esterase patterns among populations of Bemisia tabaci, and the association of one population with silverleaf symptom induction

“…observ.). In Florida, SSL has been associated with feeding by B. tabaci (Maynard & Cantliffe, 1989;Yokomi et al, 1990) and the presence of two double-stranded RNAs (Bharathan et al, 1990). However, the etiology of this disorder is unknown.…”

Biotype‐specific expression of dsRNA in the sweetpotato whitefly

“…Following the association of SPW with SSL, two divergent hypotheses were advanced to explain this disorder. Bharathan et al (1990) reported two double-stranded RNAs (dsRNA; 4.6 and 4.2 kilobase pairs, Kb) in leaf extracts from symptomatic plants and implicated this foreign nucleic acid as the causal agent of whiteflyinduced SSL. Yokomi et al (1990) also discovered dsRNA (4.4 and 4.0 x 106 mol wt), but this nucleic acid was only found in the SPW; dsRNA was not found in symptomatic leaves.…”