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Disease Detection and Losses

Variation in the Distribution of Citrus Ringspot and Psorosis Viruses Within Citrus Hosts. L. W. Timmer, Associate professor, Texas A&I University Citrus Center, Weslaco, TX 78596, Present address of senior author: University of Florida, Institute of Food and Agricultural ScienceľAgricultural Research and Education Center, P.O. Box 1088, Lake Alfred, FL 33850; S. M. Garnsey, research plant pathologist, Federal Research, Science and Education Administration, U.S. Department of Agriculture, Orlando, FL 32803. Phytopathology 69:200-203. Accepted for publication 22 August 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-200.

Some isolates of citrus ringspot virus (CRSV) in Texas were inconsistently graft-transmitted from twig bark of infected mature grapefruit trees to greenhouse-grown citrus indicator seedlings. These isolates usually were transmitted with inoculum from twigs on which foliar symptoms were apparent or from the psorosis-like bark lesions on the primary branches of CRSV-infected trees. In two grapefruit trees with small, initial bark lesions on the primary branches, the virus was transmissible only from the portions of the branches with lesions. Mechanical transmission of some Texas isolates from symptomatic young citrus leaves produced abundant local lesions on Chenopodium quinoa, whereas few or no lesions were produced when symptomless leaves were used. Graft transmission of one Florida isolate of CRSV by leaf pieces to citrus seedlings and by mechanical transmission to C. quinoa from symptomless young leaves failed, whereas transmission from symptomatic leaves was successful. This isolate was irregularly distributed even within symptomatic leaves, and could not be transmitted to C. quinoa from symptomless areas of such leaves. Citrus psorosis virus and two CRSV isolates from Florida were recovered more consistently from symptomless tissue. Although several citrus hosts and C. quinoa are excellent indicator plants for CRSV, indexing methods used for other citrus viruses have been useful only to confirm infections that were already suspected from visual inspection.