Spread of Citrus Tristeza Virus in a Heavily Infested Citrus Area in Spain

Abstract

Spread of Citrus Tristeza Virus (CTV) in a heavily infested citrus area in Southern Valencia (Spain) has been monitored since 1981. Two adjacent plots with 400 trees each were selected and tested yearly by ELISA (enzyme-linked immunosorbent assay). One of them was planted to 4-yr-old Newhall navel orange on Troyer citrange and the other to 8-yr-old Marsh seedless grapefruit on the same rootstock. Both had been established using virus-free budwood. In 1981, 98.7% of the Newhall navel plants indexed CTV-positive and by 1984 all of them were infected, whereas only 17.8% of the Marsh grapefruit indexed CTV-positive in 1981, and 42.5% were infected in 1986. This is an indication that grapefruit is less susceptible than navel orange to tristeza infection under the Spanish field conditions. Wild plants of 66 species collected in the same heavily tristeza-infested area were also tested by ELISA to find a possible alternate non-citrus host. CTV was not found in any of the more than 450 plants analyzed.