EFFECTS OF BARLEY YELLOW DWARF VIRUSES AND SNOW MOLDS ON YIELD STABILITY OF WINTER CEREALS

A four-year study was carried out to examine the interaction between i nfections of barley yellow dwarf viruses (BYDVs) and snow molds and to assess the relative importance of these two diseases in winter cereal s. A factorial experiment was arranged as a split-split-plot design wi th insecticide or BMYVs in main plots, genotypes in sub-plots and fung icide or snow mold in sub-subplots. A mixture of BYDV-PAV and BYDV-MAV virus isolates was used for infection with viruliferous Rhopalosiphum padi aphids. Three winter rye cultivars, Kodiak (tolerant (T) to BYDV s), Horton (T), and Musketeer (T), four winter triticale lines, OAC Wi ntri (T), GWT-112 (T), GWT-133 (sensitive (S)), and 3194 (S), and thre e winter wheat cultivars, Elmo (moderately tolerant), Lennox (S), and Fredrick (S) were evaluated. Although BYDVs appeared to reduce winter survival only slightly, their effects on other agronomic characters we re important. In contrast, snow mold killed the plants in the spring, affecting both winter survival and agronomic characters. Joint infecti ons of BYDVs and snow mold caused further damage. The study showed tha t tolerance to BYD and snow molds are both of primary importance to im prove yield stability of winter cereals in deep snow covered areas of Quebec.