Molecular Analyses of Citrus tristeza virus Subisolates Separated by Aphid Transmission

Abstract

Citrus tristeza virus (CTV) exists in field isolates as a complex of virus isolates. This complex may contain both mild and severe CTV. Using single and multiple aphid transmissions, subiso-lates of the various field isolates were separated. Some CTV isolates that tested negative with the monoclonal antibody MCA13 consisted of MCA13-positive subisolates. Using primers to specific and variable regions of the CTV genome, molecular profiles of the isolates and subisolates were generated and compared. The profiles of the subisolates sometimes were very different from the parent field isolates from which they were transmitted.

Evaluation of the protective capacity of new mild Citrus tristeza virus (CTV) isolates selected for a preimmunization program

“…This finding is in agreement with the results found by Brlansky et al (2003), in which severe strains that were part of a mild viral complex were transmitted by a vector. Inverse results were observed by Velazquez- Monreal et al (2009).…”

“…The genetic profiles of three Florida CTV isolates were studied in three citrus host species. The profiles of these isolates were not altered by graft transmission (Broadbent et al, 1996;Brlansky et al, 2003;Roy and Brlansky, 2009). Thus, it is presumed that the small time between the vector inoculation and the collection of the samples for the molecular analysis (in comparison with the exposition time of the plants in the field) leads to the rapid observation of the electrophorectic profiles of the vector challenged plants.…”

“…In fact, this process may explain the high genetic variability observed under field conditions and the observed pathogenicity alterations (Ayllón et al, 1999;Brlansky et al, 2003;Velazquez-Monreal et al, 2009). The field experiment evaluations showed that challenge inoculation by tissue union with the severe isolate lead to severe tristeza symptoms with high stem pitting and leaf symptom scores and low vegetative development scores ( Table 2).…”

“…Although the characterization of the CTV isolates by sequencing the virus' coat protein gene is extensively useful, the sequence comparison of a single gene or region may reflect differences that are only found in this region. As such, this technique may not take into account the remaining genoma (Brlansky et al, 2003) that can hide the greater differences that are expressed in certain conditions.…”

“…Furthermore, the composition or balance of the CTV isolates within the host may be altered by the viral genome interaction, citrus host variety, environment conditions and by multiple aphid infections. Thus, a CTV isolate that shows mild symptoms when indexed biologically may contain one or more severe haplotypes that could express severe symptoms under certain conditions (Brlansky et al, 2003;Folimonova et al, 2010;Roy and Brlansky, 2009;Velazquez-Monreal et al, 2009).…”