Discovery of a Strain of Tristeza Virus (K) Inducing No Symptoms in Mexican Lime

Abstract

In a rootstock trial, six kumquat cultivars were grafted on trifoliate orange and on Troyer citrange.All six cultivars did well on trifoliate orange, but only one thrived on citrange.This finding prompted us to search for potential viruses in our kumquat cultivars.In addition to indexing on indicator plants, we looked for inclusion bodies and found that two kumquat trees on trifoliate orange had inclusion bodies in the phloem, suggesting citrus tristeza virus (CTV) infection.ELISA (enzyme-linked immunosorbent assay) tests were positive for CTV using antibodies to the Reunion strain of CTV.Filamentous virions similar to CTV could be seen by electron microscopy in the phloem of the two kumquat trees and were purified from young shoots.The purified virions were ultrastructurally and serologically indistinguishable from typical CTV.These results prove that the two kumquat trees are infected with a strain of CTV referred to here as strain K.The two CTV-positive kumquat trees were among three trees introduced to Corsica from Morocco in 1959.These trees indexed negatively on Mexican lime seedlings in 1963 and were considered free from CTV.When it was realized in 1981 that two of the three trees were infected with CTV, they were again indexed on Mexican lime seedlings in Corsica and Bordeaux.No vein clearing or stem pitting was observed, but ELISA showed that the limes were infected with CTV.Because strain K is symptomless on Mexican lime CTV infection in the two kumquat trees was not detected earlier.Indexing by ELISA has shown that no spread of CTV has occurred from the two initial kumquat trees or their progeny.