VIEW ARTICLE

Disease Detection and Losses

Serological Detection of Cherry Leafroll Virus in English Walnut Trees. Adib Rowhani, Postgraduate research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of California, Davis 95616; S. M. Mircetich(2), R. J. Shepherd(3), and J. D. Cucuzza(4). (2)(4)Research plant pathologist, and postgraduate research plant pathologist, respectively, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of California, Davis 95616; (3)Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 75:48-52. Accepted for publication 25 June 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/Phyto-75-48.

Direct (D) and indirect (I) enzyme-linked immunosorbent assays (ELISA) were compared for relative reliability in detecting the walnut strain of cherry leafroll virus (CLRV-W), the causal agent of blackline disease in English walnuts. The lowest concentrations of purified CLRV-W8 detected by I-ELISA and D-ELISA with peroxidase-conjugated γ-globulin were 4 ng/ml and 48 ng/ml, respectively, of the virus in phosphate buffer, pH 6.5. Likewise, based on the highest dilution of CLRV-W-infected walnut inner bark tissue and pollen in PBS-Tween buffer at which the virus was detected, I-ELISA was 8 and 16 times more sensitive than D-ELISA, respectively. I-ELISA with peroxidase and alkaline phosphatase was more sensitive than I-ELISA with glucose oxidase for detection of the known concentrations of purified CLRV-W8 or of the virus in infected walnut tissues. I-ELISA with γ-globulin-peroxidase conjugate is efficient and reliable for indexing English walnut seedlings in nurseries for CLRV-W. It also was reliable in detecting CLRV-W in naturally infected orchard trees when a relatively large amount of pollen from each tree (avg 80 g per tree) was collected from which 0.1 g was used for I-ELISA tests. However, the detection of CLRV-W by I-ELISA in orchard trees was not reliable when a relatively small amount of pollen from each tree (avg 5 g per tree) was collected for the assay. The relatively large amount of pollen from each tree was necessary for reliable I-ELISA tests to compensate for the uneven and erratic distribution of CLRV-W in naturally infected walnut orchard trees.