Tomato spotted wilt Tospovirus genome reassortment and genome segment-specific adaptation.

A system to associate specific genome segments with viral phenotypes and to study factors influencing genome reassortment was developed for tomato spotted wilt Tospovirus (TSWV). Reassortant isolates were generated by co-inoculating a TSWV isolate, TSWV-D, with TSWV-10 or TSWV-MD. The parental origin of each genome segment in putative reassortant isolates was determined by segment-specific restriction fragment length polymorphisms. The TSWV isolates readily exchanged genome segments in a nonrandom fashion. The S RNA from TSWV-D was dominant over the S RNA from TSWV-10. The intergenic region (IGR) of the S RNA was correlated with competitiveness of this genome segment in reassortant isolates. The less competitive S RNA contained a net increase of 62 nt, including a 33-nt duplication in the IGR. This duplicate sequence was highly conserved among isolates from the southeastern United States and an isolate from Bulgaria. The evidence supports the hypothesis that the IGR of the S RNA with an ambisense coding strategy serves a regulatory function which influences the occurrence of this segment in the viral population. In addition, it was demonstrated that stable parental phenotypes can be mapped to specific genome segments as well as generating novel phenotypes not associated with either parent.

Pathogenesis of Tomato Spotted Wilt Virus in Peanut Plants Dually Infected with Peanut Mottle Virus.

Peanut (Arachis hypogaea) plants dually infected with tomato spotted wilt tospovirus (TSWV) and peanut mottle potyvirus (PMV) exhibited a wide variety of symptoms, ranging from PMV-like symptoms of transient mild leaf mottle to TSWV-like symptoms of severe leaf distortion and stunting of the plant. Dual infection did not cause greater symptom severity than infection with either virus alone. In the early stages of disease development, PMV symptoms were similar to the first leaf symptoms of TSWV infection, suggesting that identification of TSWV in field-grown peanuts should not depend on visual observation. The virus titer, determined by enzyme-linked immunosorbent assay, indicated a delay in TSWV disease progress in doubleinfected plants, compared to plants infected with TSWV alone. In the later phase of disease progress, the virus titer in dually infected plants was not significantly different from that of singly infected plants. Infection with TSWV and PMV alone and with both viruses in combination was consistent among commercially grown peanut cultivars. In plants inoculated with TSWV or PMV alone or with both viruses in combination, the length of the latent period and final disease incidence, as measured by the number of plants showing symptoms, did not depend on the cultivar.

Purification and coat protein gene sequence of a Montana RMV-like isolate of barley yellow dwarf virus.

A Montana barley yellow dwarf virus (BYDV) isolate, BYDV-RMV-MT, is serologically identical to the New York RMV type isolate (RMV-NY) but differs in aphid transmission phenotype. A purification procedure for BYDV-RMV-MT was developed and cDNAs encompassing the entire coat protein gene and a portion of the putative polymerase gene of both RMV-MT and RMV-NY were cloned and sequenced. Diameters of RMV-MT virions averaged 24.7 nm. Average virus yield was 4.2 mg/kg plant tissue. There was 81% sequence identity between the clones of MT and NY RMV isolates at the nucleotide level. At the amino acid level the polymerase genes were 91% identical to each other and 74% homologous with that of beet western yellow virus. The coat protein amino acid sequences of the two RMV isolates were only 81% identical and, compared to other sequenced luteoviruses, both were most similar to cucurbit aphid-borne yellows virus.