BARLEY YELLOW DWARF VIRUS MULTIPLICATION AND HOST-PLANT TOLERANCE IN DURUM-WHEAT

A Canadian PAV-like isolate of barley yellow dwarf virus (BYDV) was us ed to infect durum wheat (Triticum durum) cultivars previously identif ied in field trials involving artificial inoculation as highly sensiti ve (12 IDSN74), slightly tolerant (La Dulce), and relatively tolerant (Boohai and 12 IDSN227) to BYDV. The cultivars were inoculated in the greenhouse as seedlings, and indexed for virus accumulation by enzyme- linked immunosorbent assay (ELISA) at various intervals between 3 and 60 days thereafter. Mean ELISA values were somewhat consistent with to lerance levels for 4 durum wheat cultivars, but the use of ELISA to sc reen for BYDV resistance in durum wheat is not practical. The magnitud e of the difference between sensitive and tolerant cultivars for the m ean ELISA value is not high enough, and it may be necessary to average readings between 3 and 60 days after inoculation to obtain somewhat m eaningful ELISA data. The effect of vector aphid numbers on virus titr e and aerial biomass in the sensitive durum wheat cv. Karim was also e valuated. There was no significant effect on virus content in a prelim inary trial, but a second trial revealed that more viruliferous aphids per plant resulted in higher ELISA values. Infestation with 32 or 50 viruliferous Rhopalosiphum padi per plant depressed biomass yield belo w the level observed with 1-10 aphids per plant.