Developing an understanding of cross-protection by Citrus tristeza virus.

Svetlana Y Folimonova

doi:10.3389/fmicb.2013.00076

Abstract

Citrus tristeza virus (CTV) causes two citrus diseases that have caused devastating losses in global citrus production. The first disease is quick decline of trees propagated on the sour orange rootstock. The second disease is stem pitting, which severely affects a number of economically important citrus varieties regardless of the rootstock used and results in reduced tree growth and vigor as well as in reduced fruit size and quality. Both diseases continue to invade new areas. While quick decline could be effectively managed by the use of resistant and/or tolerant rootstocks, the only means to protect commercial citrus against endemic stem pitting isolates of CTV has been cross-protection with mild isolates of the virus. In some citrus areas cross-protection has been successful and allowed production of certain citrus cultivars despite the presence of severe stem pitting isolates in those regions. However, many other attempts to find isolates that would provide sustained protection against aggressive isolates of the virus had failed. In general, there has been no understanding why some mild isolates were effective and others failed to protect. We have been working on the mechanism of cross-protection by CTV. Recent considerable progress has significantly advanced our understanding of how cross-protection may work in the citrus/CTV pathosystem. As we demonstrated, only isolates that belong to the same strain of the virus cross protect against each other, while isolates from different strains do not. We believe that the results of our research could now make finding protecting isolates relatively straightforward. This review discusses some of the history of CTV cross-protection along with the recent findings and our “recipe” for selection of protecting isolates.

Highlights

Citrus tristeza virus (CTV) is the largest and most complex member of the family Closteroviridae, which contains viruses that cause severe economic losses in crops including vegetables, grains, grapes, and fruit trees (Bar-Joseph et al, 1979; Dolja et al, 1994, 2006; Agranovsky, 1996; Karasev, 2000)
Earlier we developed a green fluorescent protein (GFP)expressing CTV vector based on an infectious cDNA clone of CTV T36, the type isolate of the T36 strain (Folimonov et al, 2007; GFP-T36 CTV )
When citrus trees pre-infected with an isolate of one of the five genotypes of CTV (T30, T3, T68, VT, or T36) were sequentially challenged with GFP-marked T36 CTV, all of them with the exception of the plants that were initially infected with isolates of the latter T36 genotype displayed GFP fluorescence similar to that observed in control plants that had no primary infection and were inoculated only with the challenge virus (Figure 2)

Summary

Introduction

Citrus tristeza virus (CTV) is the largest and most complex member of the family Closteroviridae, which contains viruses that cause severe economic losses in crops including vegetables, grains, grapes, and fruit trees (Bar-Joseph et al, 1979; Dolja et al, 1994, 2006; Agranovsky, 1996; Karasev, 2000). One of the first examples of the commercial exploitation for prevention of severe viral infections was cross-protection against severe CTV stem pitting with mild virus isolates (Grant and Costa, 1951).

Results

Conclusion