Barley yellow dwarf virus (BYDV) is one of the most damaging and economically important virus infecting grain cereals. It infects a great number of Poaceae species, causing yield losses of up to 15- 25% in barley. BYDV is transmitted by aphids in a circulative, non-propagative manner. Nowadays, to prevent the plants from becoming infected with BYDV, pesticides are used to fight against aphid infestation. Even though pesticides are effective, they are not a sustainable solution. Thus, plant breeding for resistance and tolerance can be a good substitute or complementary measure to pesticides. Resistance and tolerance have been studied for a long time, but the durability of resistant and tolerant cultivars is still a work in progress. In order to improve the management of the disease, we have worked on two projects. First, to better understand past BYDV outbreaks, we have sampled forty-five herbarium specimens of wild Poaceae species (Poa nemoralis and Lolium perenne) dating from the 1980s and coming from the Botanic Garden of Meise (Belgium). Then, we have performed total RNA extraction of the samples in order to recover old BYDV genomes and compare them with modern ones. Unfortunately, no BYDV was found in the samples. The goal of the second project was to assess and compare the tolerance level of four new non-commercialised barley cultivars tolerant to BYDV (KWS, LGBB, Novira, Paradise), as well as an already commercialised tolerant cultivar (Rafaela) and a sensitive cultivar (Tropic). Fifteen plants from each cultivar have been infected with BYDV. Then, eighteen days after inoculation, measures of stem length and plant weight have been performed to assess the effect of viral infection on plant health. The relative viral concentration in each plant has been measured using quantitative ELISA. Using plant health and viral accumulation measures, the tolerance level of each cultivar has been assessed with two methods called “regression range” and “two points range” tolerance. Our results showed that, in our case, “regression range” tolerance is a better method than “two points range” tolerance to distinguish the cultivars according to their tolerance levels. Divergent levels of tolerance to BYDV have been identified between the cultivars. Novira is the most tolerant cultivar and overcompensates detrimental effects of the pathogen, whereas LGBB is the less tolerant cultivar. While developing new resistant or tolerant cultivars is important, future investigation should be carried on how resistance and tolerance affect the evolution of BYDV.

Curs 2018-2019