Tripartite interactions of Rice stripe necrosis virus, Polymyxa graminis and Oryza sativa

Rice stripe necrosis virus (RSNV) is the causal agent of the rice crinckle disease. Considered as an (re-)emerging virus in South America and West Africa, little data are available on the virus, and especially how the virus interact with its host plant and its plasmodiophorid vector, Polymyxa graminis. The tripartite interactions between RSNV, P. graminis and Oryza sativa has been investigated to confirm experimentally the acquisition and transmission of the virus by this vector protist. The analysis of the genetic diversity of the new sequences obtained, presents two main lineages of RSNV emerging in America and re-emerging in Africa. The genetic diversity of the RNA2 segment of RSNV and BNYVV were similar except for an in-frame insertion of 243 nucleotides located in the RSNV tgbp1 gene, whereas the RNA1 segment showed higher nucleotide variability for RSNV than for BNYVV. The RSNV transmission vector, P. graminis f. sp. colombiana, was found highly associated with Oryza sativa and O. glaberrima, but is also found, to a lesser extent, on a wider host range including Zea mays, Sorghum bicolor, Pennisetum glaucum, and Triticum durum as well as with some rice field weeds. while Polymyxa multiplies in different hosts, the virus is only transmitted to rice. Sequences of the 28 S, beta tubulin, eF1- alpha, L10 and RSP5 40s genes have been used in addition to the full-length sequences of ITS, and 5.8 S to propose a multi-locus sequence analysis as a tool for the precise diagnostic of rice associated Polymyxa. In this thesis, a first demonstration of the acquisition and transmission of RSNV by P. graminis under experimental conditions. The thesis is now opening the field for screening rice varieties for resistance against the virus and/or its vector, as well for proposing biologically based management strategies for the rice crinckle disease.
(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2022