Diversity of soil-borne sugar beet viruses in Iran
(2009)
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- Authors
- Supervisors
- Bragard, Claude
- Abstract
- (en) Soil-borne sugar beet viruses are responsible for destructive diseases of sugar beet. They can cause significant yield losses worldwide. Four of them, the Beet necrotic yellow vein virus, the Beet soil-borne mosaic virus, the Beet soil-borne virus and the Beet virus Q are transmitted by Polymyxa betae, a common root-infecting parasite that ensures the long-term persistence of viruses in soils. And one of them the BBSV is transmitted by Olpidium brassicae. The objective of this thesis was to study the presence and diversity of these viruses in Iran, with the view of analysing the level of their genetic diversity for a better understanding of their pathogenicity, distribution and evolution. Using a smart sampling strategy for targeting sugar beet fields presenting soil-borne viral diseases, four different telluric viruses have been mapped in Iran. This study allowed verifying the widespread presence of BNYVV the causal agent of rhizomania disease in the country. Nine different tetrads in the p25 of the RNA3 of BNYVV A-type were recorded. Furthermore, the presence of the pathotype P of BNYVV in numerous soils was indicative of the presence of aggressive BNYVV isolates. BNYVV was found to be associated with three other viruses. First of all, and even if their contribution to the etiology remains a matter of debate, pomoviruses like BSBV and in a lesser extend, BVQ, usually associated with rhizomania, have been found quite frequently for a country with warmer areas. Their contribution to the disease remains to be clarified, but this work contributed to the elaboration of BSBV full length clones which shall be used in a reverse genetic strategy to elucidate their role in the pathogenic process alone or in combination with BNYVV or BBSV. Finally, BBSV and BBSV satellite was discovered for the first time in Iran. This work is describing the genetic diversity of this Necrovirus, and its satellite. The detection of a sequence homologous in BBSV satellite to the Argonaute gene and its relative similarity with similar gene lying within the sugar beet genome stress the specific interactions between the virus and its plant host and possibly the involvement in the suppression of the gene silencing by targeting the core of the system itself. Furthermore, it was shown that a single Adenine within the 3’UTR is probably linked to the ability to act concurrently with the satellite. A major question regarding BBSV is its ability to cause symptoms like black scorching on sugar beet. Here it was shown that the virus is able to cause strong symptoms on several host plants and that specific isolates induced black scorching on common sugar beet cultivars, even those bearing resistance genes to BNYVV. By reverse genetic the role of coat protein in the formation of symptom of black scorching was demonstrated and it was suggested that the BBSV is an avirulence factor able to trigger the hypersensitive reaction of the host plant supposedly through ingle changes in the amino acids sequence of the CP gene.
- Affiliations
Citations
Mehrvar, M. (2009). Diversity of soil-borne sugar beet viruses in Iran. https://hdl.handle.net/2078.5/128774