First report of Citrus viroid v naturally infecting grapefruit and calamondin trees in California.
The Citrus Clonal Protection Programme-National Clean Plant Network, University of California, Riverside (UCR), received citrus budwood samples in June 2016 from the California Department of Food and Agriculture (CDFA) for virus and viroid testing under the mandatory California (CA) Citrus Nursery Stock Pest Cleanliness Programme. Samples originated from nonsymptomatic budwood sources, two redblush grapefruit (Citrus paradisi) and four variegated calamondin (C. madurensis), and were found in a nursery in Tulare County, CA. Reverse transcription polymerase chain reaction, cloning, sequencing and pathogenicity tests revealed the presence of Citrus viroid V (CVd-V). The CVd-V identification results were independently verified by CDFA's Plant Pest Diagnostic Centre, and the original source trees were destroyed. CVd-V was first reported in Spain and has been detected in various samples including a source from UCR, but the source of the UCR field material was not recorded. This note reports the natural occurrence of CVd-V in CA and corroborates the CVd-VCA variant report from the UCR source. This note also demonstrates the importance of regulatory testing of propagative materials and elimination of infected citrus germplasm source trees to prevent the spread of viroids into commercial citrus.