RESULTS FROM A THREE YEARS FIELD TRIAL PLANTED AT CONCORDIA, ARGENTINA USING TRANSGENIC ROOTSTOCKS POTENTIALLY RESISTANT TO TRISTEZA

Citrus tristeza virus (CTV) causes one of the most devastating diseases of citrus worldwide. It induces the death of sweet orange, mandarin, lime and grapefruit trees budded on sour orange which has caused its replacement by other CTV-tolerant rootstocks. The availability of a CTV-resistant rootstock with the sour orange attributes of productivity, fruit quality and tolerance to abiotic stresses would be a major benefit to the citrus industry worldwide. The objective of this work was to evaluate the response to CTV of 10 sour orange (Citrus aurantium) transgenic lines carrying CTV-derived sequences. They were obtained in the laboratories of IVIA, Spain and planted at INTA Experiment Station in Concordia, Argentina, where CTV is endemic and efficiently transmitted by the brown citrus aphid (Toxoptera citricida). Trees were obtained by budding rooted cuttings of transgenic sour orange lines with non-transgenic and virus-free Valencia late sweet orange (C. sinensis). Valencia trees budded on tolerant rootstocks as well as non-transgenic sour orange were planted as controls. Trees were planted in a complete randomized design with two trees per plot and 5 replications. Every six months imprints were taken to determine the progress of CTV infection in each tree. Four years after planting, almost 100% of the trees are CTV infected, showing stunting growth and yellowing of foliage.