Spread of Citrus Tristeza Virus in Citrus Orchards in Central California

Abstract

<jats:p> In California, citrus tristeza virus (CTV) is regulated by a State Interior Quarantine. In CTV abatement districts in central California, trees with CTV that react to MCA13 (MCA13-positive [MCA13+]), a strain-discriminating monoclonal antibody, are rogued to prevent virus spread. The Tulare County Pest Control District, however, does not participate in this abatement program except for a 1.6-km<jats:sup>2</jats:sup> zone around the Lindcove Research and Extension Center, Exeter, CA. To quantify CTV spread under these two disparate management programs, CTV surveys were conducted in abatement plots with mandatory aphid control and nonabatement plots. Abatement plot surveys used hierarchical sampling of 25% of trees with samples pooled from four adjacent trees. Detection of MCA13+ CTV in a sample prompted resampling and testing of individual trees. From 2008 to 2018, incidence of CTV increased by an average of 3.9%, with only two MCA13+ samples detected. In contrast, in nonabatement plots, incidence of CTV increased by an average of 4.6% between 2015 and 2018. Increase in MCA13-negative (MCA−) isolates was 11 times greater than that of MCA13+ isolates, with the number of MCA13+ trees increasing by 19 trees between 2015 and 2018. MCA13− isolates were more randomly distributed, suggesting primary spread, whereas MCA13+ CTV isolates were more aggregated, suggesting some secondary spread. These results suggest that spread of MCA13+ isolates was limited by a combination of tree removal and aphid vector suppression. MCA13+ samples were VT isolates with some mixtures with T30 isolates. Despite the presence of VT isolates, all CTV-infected trees were asymptomatic. </jats:p>

Effects of Two Citrus Tristeza Virus Isolates on Sweet Orange (Citrus sinensis) Propagated on a Citrus Tristeza Virus Tolerant Rootstock: A Metabolomics and Transcriptomics Approach

“…Both isolates originated in California. The mild strain, T30 isolate 07539, is endemic to California citrus, and the stem-pitting strain (CCTEA-107) was found previously in California groves and subsequently eradicated . Each CTV isolate was maintained in Valencia orange [ C. sinensis (L.) Osbeck “Valencia”] as source plants for graft inoculation from infected budwood.…”

Complete genome sequencing and characterization of a potential new genotype of Citrus tristeza virus in Iran

“…aurantii , A . craccivora , and Myzus persicae [ 4 – 6 ]. Other spread pathways include graft transmission and plant material infested with aphid vectors [ 7 ].…”

Survey estimates of the incidence and diversity of Citrus tristeza virus in California

“…Through these programs and the cooperation of growers and citrus nurseries, CTV causes little significant economic damage in California (O'Connell et al 2010;Yokomi et al 2020) except for occasional occurrences of QD of citrus planted on sour orange rootstock. To investigate the present status of CTV in California, we conducted surveys of CTV in commercial citrus orchards in all major citrus-growing counties in California to estimate the incidence and determine the genotypes of CTV present.…”