Survey of stem pitting Citrus tristeza virus in commercial citrus groves in Florida

Citrus tristeza virus (CTV) has affected how citrus is grown in Florida since the 1950s. The brown citrus aphid, first detected in Florida in 1995, is an efficient vector of CTV and is capable of spreading severe forms of CTV throughout the state. The use of molecular markers for CTV led to the discovery of aphid transmitted stem-pitting forms of CTV (SP-CTV) in Polk County, central Florida. A survey to determine if SP-CTV was present was undertaken for the eleven counties representing 80% of commercial citrus production in Florida. Five sweet orange and two grapefruit sites per county were surveyed using a hierarchical bulk sampling procedure. Immuno-capture reverse transcriptase polymerase chain reaction (ICRT-PCR) with Type 11 primers was used for initial screening followed by other SP-CTV markers for positive samples. Fifty-five percent (42 of 77) of the sites surveyed tested negative in all samples. The majority of sites testing positive, 61%, had a less than a 5% chance of any single tree in that block testing positive. Only six sites had a greater than a 10% chance of any one tree testing positive for the SP-CTV markers. There were two main pattern profiles of markers present. Not all of these isolates have been evaluated in biological indicators so whether they can cause significant damage and what their threat is to the citrus industry has yet to be determined. Currently, a strong Citrus Budwood Registration Program and increasing the number of budwood source trees under protective screen will prevent the spread of severe forms of CTV throughout the nursery industry.