Disease Note.

Quick Decline Symptoms Confirm Presence of Citrus Tristeza Virus Decline Isolates in Puerto Rico. R. K. Yokomi, USDA, ARS, Horticultural Research Laboratory, 2120 Camden Rd., Orlando, FL 32803 . S. M. Garnsey, USDA, ARS, Horticultural Research Laboratory, 2120 Camden Rd., Orlando, FL 32803; and P. A. Stansly, University of Florida, Immokalee 33934. Plant Dis. 80:1207. Accepted for publication 10 July 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1207A.

Citrus in Puerto Rico is an important crop grown for local consumption. Because of the threat of aphid-borne citrus tristeza virus (CTV), most commercial citrus on the island in the past 10 years have been planted on CTV-tolerant rootstocks, especially Cleopatra mandarin (Citrus reticulata Blanco). However, small plantings on CTV-sensitive sour orange, C. aurantium L., rootstock are also present. The efficient CTV vector, Toxoptera citricida (Kirkaldy), was first detected in Puerto Rico in April 1992 (I). During the following 3-year period, a total of 1,818 individual trees have been sampled throughout the island to determine changes in incidence of CTV. Each survey sample was assayed by enzyme-linked immunosorbent assay (ELISA) with a differential panel of monoclonal and polyclonal antibodies. The incidence of CTV increased from 5 to 58% during the 3-year survey. The number of samples that reacted with the severe-strain discriminating monoclonal antibody, MCA 13, increased from 1.4 (3 of 221 trees) to 26% (62 of 240 trees) during this period. These data suggested the presence of severe CTV strains capable of causing decline on sour orange rootstock, but no outbreaks had yet occurred. In May 1996 (4 years after the aphid's establishment), the first outbreak of CTV-induced decline was detected in a 36.4-ha citrus planting near Lares, Puerto Rico. Nearly all trees in previously productive blocks of 4- and 5-year-old Valencia orange on sour orange rootstock totaling 8.5 ha (approximately 3,400 trees) were affected with quick decline. Positive diagnosis was made on the basis of (i) pathology at the bud union of declining trees including inverse pinhole pitting (honeycombing) on the inner face of the sour orange bark and a yellow-brown discoloration at the bud union; (ii) off-season blossoms; and (iii) foliar symptoms indicative of a complete girdle above the bud union. Adjacent plantings of the same age or older on mandarin or other CTV-tolerant rootstocks did not show CTV-decline symptoms and remained productive. The presence of CTV antigen from all trees sampled in the declining block and adjacent trees was confirmed by ELISA. Samples from 4 of 5 declining trees and 4 of 5 surrounding trees on tolerant rootstock reacted with MCA 13, suggesting the presence of a severe CTV strain. CTV isolates that reacted with MCA13 had previously been detected in a nearby citrus nursery in 1993.