Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2011
Publication Date: 8/1/2011
Citation: Brlansky, R.H., Avijit, R., Damsteegt, V.D. 2011. Stem pitting Citrus tristeza virus predominantly transmitted by the brown citrus aphid from mixed infections containing non-stem pitting and stem pitting isolates. Plant Disease. 95:913-920. Interpretive Summary: Citrus tristeza virus (CTV) is the most destructive and widely spread virus attacking Citrus. The virus produces a variety of symptoms in various Citrus species including stem pitting, vein flecking, seedling yellows, tree decline, reduced fruit size and yield, and tree death. The most efficient transmitter of all strains of the virus is the brown citrus aphid (BCA). Wherever the brown citrus aphid is found, severe strains of CTV are found. In order to determine if the BCA transmits the severe forms more frequently than mild forms of the virus, single and multiple aphid transmissions were performed on Citrus plants grafted with mixtures of severe and mild strains of the virus. Biological and molecular data were obtained from the test plants and the source plants and genetic profiles were generated. Results of the analyses indicate that some CTV isolates may arise from doubly infected plants. The severe stem pitting strains were more frequently transmitted by the BCA than milder strains confirming the earlier observations that severe strains of CTV appear when the BCA is established in a Citrus production area. These results will help producers identify and diagnose trees with severe pitting strains, when the BCA is present.
Technical Abstract: Citrus tristeza virus (CTV) is a phloem-limited closterovirus that produces a variety of symptoms in various Citrus spp. One of these symptoms is stem pitting (SP). SP does not occur in all Citrus spp. but when it does it may cause low tree vigor, decline and an economically-significant reduction in fruit size and yield. Historically, the first appearance of CTV-SP in a citrus area often occurs after the introduction of the most efficient CTV vector the brown citrus aphid (BCA) Toxoptera citricida (Kirkaldy). Hypotheses for this association ranges from the introduction of these strains in new planting materials to the increased ability of T. citricida to transmit SP strains from existing CTV sources. It is known that CTV often exists as a complex of isolates or subisolates. Single and multiple BCA transmissions have been used to separate different genotypes or strains of CTV from mixed CTV infected plants. This study was initiated to determine what the BCA transmits when a severe SP exotic CTV isolate B408 from Dominican Republic or B12 from Brazil is mixed with a non-SP (NSP) FS627 isolate from Florida. Biological and molecular data were generated from grafted mixtures and their aphid transmitted subisolates. The single strand conformation polymorphism (SSCP) profiles of NSP and SP grafted plants remained unchanged, but the profile of doubly inoculated plants varied. The SSCP profile was constant in plants that showed SP symptoms. The genetic diversity within SP isolates B12, B408 and mixtures of NSP and SP isolates (FS627/B12 and FS627/B408) and aphid transmitted subisolates of doubly inoculated plants was determined by analyses of the genetically related variants (haplotype) nucleotide sequences. Comparison of these haplotypes with other isolates using phylogenetic analysis suggests that some CTV isolates may arise from infection of divergent isolates. Aphid transmissions, symptoms and molecular analyses showed that SP-CTV was more frequently or dominantly transmitted with or without NSP-CTV from mixed infections.