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Published in Phytopathology 77:10 (October 1987), pp.1435-1437. Copyright 1987 The American Phytopathological Society.


Single and mixed infections by Pyrenophora teres and two isolates of barley yellow dwarf virus (BYDV) were evaluated for their effects on the resistance to freezing stress of crowns of the winter barley cultivar Pennrad. Plants received one of several treatments: P. teres; either the RMV-NY or PAV-NY isolate of BYDV; RMV + P. teres; PAV + P. teres; or infestation with either nonviruliferous Rhopalosiphum maidis or R. padi. After the treatments, foliage and roots were harvested from 4-wk-old plants to evaluate the effects of infection(s) on top and root growth before freezing. The crowns were subjected to a controlled freezing regime, and resistance to freezing stress was evaluated by assessing retardation of shoot and root regrowth after freezing (crown injury). The treatment combinations resulted in decreased plant growth before freezing and in increased crown injury, relative to control plants. Infection by P. teres did not reduce top and root growth, or lead to crown injury, to the extent of the other treatments. Feeding by viruliferous aphid species, in comparison to feeding by nonviruliferous aphid species, led to decreased top and root growth and to further crown injury. Infections by PAV + P. teres or R MV + P. teres did not reduce top and root growth, but led to increased crown injury relative to plants exposed only to viruliferous aphids.