ELISA CORRELATES WITH BIOLOGICAL INDEXING FOR THE DETECTION OF CITRUS PSOROSIS-ASSOCIATED VIRUS

Abstract

SUMMARY An ELISA kit produced at the Istituto di Fitovirologia Applicata of CNR, Torino, Italy for the detection of citrus psorosis-associated virus (CPsAV) was successfully used to test 4,499 citrus plants of different varieties in nurseries, commercial groves and a germplasm collection of Apulia (Southern Italy). One hundred and seventy trees were indexed for psorosis using ‘Madame Vinous’ sweet orange and ‘Dweet tangor’. From 60 plants that were positive by indexing, mechanical transmissions to herbaceous hosts were attempted. Psorosis was present in most of the citrus varieties, with a low incidence and distribution in commercial groves (7.4% of infected trees) and in the nurseries (4.6% of infected trees). In commercial groves, the local clementine cv. ‘Fedele’ (14.4% of infected trees) and ‘Navelina’ old clone sweet orange (9% of infected trees) were the most infected. The same rate of infection was shown by cv. ‘Fedele’ in the nurseries, whereas the highest infection rates (20.4% of infected trees) were observed in Satsuma ‘Miyagawa’. All the plants that were psorosis-positive by indexing were also positive by ELISA with the sole exception of a cv. ‘Fedele’ source. By contrast, four citrus accessions that indexed negative, were found to be positive by ELISA. Serological tests revealed a high percentage of CPsAV infections in plants indexing positive for concave gum. Only from three plants out of the 60 that indexed positive was a virus with the filamentous particles typical of CPsAV recovered by mechanical inoculation to herbaceous hosts. The demonstration that ELISA can identify psorosis in a sensitive and reliable manner, represents a step forward in favour of serological assays, which can be used for routine testing and as a complement to biological indexing in sanitary selection programmes.