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United States Department of Agriculture

Agricultural Research Service

Research Project: Characterization, Epidemiology and Management Strategies of Citrus Tristeza Virus and Spiroplasma citri on Citrus in California

Location: Crop Diseases, Pests and Genetics

Title: Molecular characterization of Cirus tristeza virus isolates associated with stem pitting CTV cross-protection in Peru

Authors
item Yokomi, Raymond
item Bederski, K -
item Roistacher, C.N -
item Giampetruzzi, A -
item Loconsole, G -
item Saponari, M -

Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 20, 2013
Publication Date: N/A

Technical Abstract: During the 1970s and early 1980s, the Peruvian citrus industry was destroyed by severe Citrus tristeza virus (CTV) strains spread by the brown citrus aphid. The Topara Nursery, located 180 km south of Lima Peru, selected and identified CTV isolates that confer cross-protection against virulent stem pitting strains of CTV. Use of CTV isolates conferring putative cross-protection may be in part or wholly responsible for revitalization of citrus production in Peru. Several protective isolates were from aphid-transmissions (AT) conducted over 26 years ago from a seedling yellows CTV strain (SY563) passed through Passiflora caerulea in California. Twenty CTV isolates, including two AT sub-isolates of SY563, were selected from protected and non-protected trees after >20 years of natural field challenge at Topara Nursery in Peru. Single-strand conformation polymorphism (SSCP) of amplicons derived from reverse-transcription polymerase chain reaction assay of the CTV coat protein gene showed various patterns, indicating strain mixtures were present in source trees. Molecular tests revealed that 18 of the 20 samples had either the VT- or T3-genotype in combination with an RB genotype. Based on source tree symptomology, SSCP patterns and CTV genotype, four samples were selected for deep sequencing analysis of small RNAs. Two draft full-length CTV genomes were reconstructed from the sequence dataset. Phylogenetic analysis confirmed the presence of genetically diverse strains in cross-protected plants. Studies to correlate presence and accumulation of different strains with regard to symptom phenology and cross-protection are continuing. The data should provide new insight on cross-protection and help to define molecular attributes of cross-protective isolates that can mitigate disease losses caused by severe CTV strains.

Last Modified: 9/22/2014
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