EFFETS D’UNE INFECTION HATIVE VS. TARDIVE DE VIRUS DU NANISME JAUNE DE L’ORGE (BYDV) SUR DES CULTIVARS D’ORGE (HORDEUM VULGARE) AVEC VS. SANS GENE YD2

BYDV (barley yellow dwarf virus) inoculated on the 16th day of growth caused much heavier losses and more grain weight reduction for cultivars without Yd2 gene. Susceptibility is strongly correlated with symptoms for this date of inoculation. Inoculation on the 34th day of growth caused heavier damage in 1974 than in 1973, and no precise symptoms occurred in 1973 despite measurable losses. Maturity is often accelerated by BYDV for cultivars without Yd2, but is generally slowed down for cultivars with Yd2. No relationship was observed between the date of maturity and the susceptibility level of cultivars possessing Yd2.