Experimental Transmission of Citrus Blight

eight healthy 6-yr-old Pineapple sweet Tucker, D. P. H., Lee, R. F., Timmer, L. W., Albrigo, L. G., and Brlansky, R. H. 1984. orange trees on rough lemon rootstock Experimental transmission of citrus blight. Plant Disease 68:979-980. from a grove in Lake Alfred unaffected by blight were pruned and transplanted Eight mature, blight-affected Pineapple sweet orange (Citrus sinensis) trees on rough lemon (C. as described. These receptor trees were jambhiri) rootstock were transplanted to an area of low blight incidence. Healthy trees of bearing planted adjacent to the donor trees with age and of the same cultivar were transplanted next to each blight-affected donor tree and several roots each of the healthy, receptor trees and the blighted donors were splice-grafted together. An the trunks about 1.2 m from those of the equal number of control trees was transplanted to an adjacent row. After 3 yr, receptor trees had donors. Five to 10 roots about 1-2 cm in significantly higher concentrations of zinc in trunk phloem than the controls. After 4 yr, seven of diameter from each receptor tree were eight receptor trees had typical visual symptoms of blight, significantly higher concentrations of splice-grafted to similar roots on the zinc in trunk wood, lower water uptake, and amorphous plugs in the vessels of the trunk. Only one corresponding donor tree. Eight additional of eight control trees developed these typical blight symptoms. This is the first report of healthy 6-yr-old Pineapple sweet orange experimental transmission of citrus blight. trees on rough lemon were transplanted similarly from the same grove as the receptor trees to an adjacent row 4.5 m Citrus blight is a vascular wilt disease trees under field conditions. Lima and from the blight-affected donors as of unknown cause. Losses from the Borducchi (6) also graft-transmitted a ungrafted controls for the root-grafted disease have been severe, reaching 'zinc accumulation factor" to young trees receptors. 500,000 trees per year in Florida, with from blight-affected sources, but these At various times during the experiment, loss rates in individual groves as high as trees did not show decline symptoms. several diagnostic techniques were used 10-20% per year (11). Progress in blight Transmission of a zinc accumulation to evaluate the status of the donor, research has been slow because blight factor was not confirmed in other studies receptor, and control trees. Canopy does not develop in trees less than 5-8 yr (13). In all previous work, no one has symptoms were rated on a scale of 0 = old and the disease has not been induced artificially induced a tree to decline from healthy, 1 = mild (leaves small with experimentally (10). In early work, blight or reproduced all of the known symptoms of zinc deficiency, internodes Rhoads (7) concluded that blight was a symptoms of the disease in a mature tree. short, slight wilt but little or no thinning nonparasitic disorder after failure to It has been generally agreed that the of foliage), 2 = moderate (leaves small, graft-transmit or propagate the disease. malady was nontransmissible (10). often flaccid, with symptoms of zinc Even after blight was more thoroughly Most studies have concentrated on deficiency, canopy sparse with some twig characterized and diagnostic tests transmission of blight symptoms to became available, bud propagations and young seedlings or propagation of the reconstitutions of blighted trees from disease by reconstituting new trees from Table 1. Diagnostic characteristics of the sprouted roots and buds of affected trees roots and buds of blight-affected trees. In blight-affected donor trees during the failed to reproduce the disease (9,13). this paper, we present the first evidence experiment. Feldman and Hanks (3) reported reduction that blight can be transmitted experiof root growth in rough lemon seedlings mentally and that all the characteristics of Characteristic Date Valuea