Effects of Light Intensity, Photoperiod, and Temperature on Symptom Expression and Host and Virus Ultrastructure inSaponaria vaccariaInfected with Carnation Etched Ring Virus

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Abstract
The expression of symptoms caused by carnation etched ring virus (CERV) on S. vaccaria was compared at different temperatures (21,27 and 32.degree. C), light levels (7532, 16,140 and 22,596 lx [700, 1500 and 2100 ft-c (foot-candle)] of cool-white fluorescent light with or without 1076 lx [100 ft-c] of incandescent light) and photoperiods (8, 12, 14 and 16 h/day). The temperature-induced differences in symptom expression also were related to temperature-induced differences in host cell and virus inclusion ultrastructure. Optimal conditions for rapid cytoplasmic inclusion formation, virus accumulation and synchronous development of red local lesions were 27.degree. C and 22,596 lx (100 ft-c) of fluorescent illumination for 14-16 h/day. High temperature, low light levels, short photoperiods and photoinduction of flowering decreased the red local lesion response in S. vaccaria. The appearance of symptoms and the rise in infectivity in inoculated plants were slower at 21 than at 27.degree. C. This was correlated with a slow rate of virus inclusion formation and virion accumulation at 21.degree. C. At 32.degree. C, chlorotic (not red) local lesions developed and a reversible temperature-induced inhibition of cytoplasmic inclusion formation was found. However, nuclear virions and intranuclear membranes accumulated at 32.degree. C and nuclear pores commonly contained virions. The formation of complex networks of interconnected chambers and expanded and extended plasmodesmata within the cell wall was temperature dependent and occurred extensively at 21 but not at 32.degree. C. When epidermal strips were treated with fluorescein isothiocyanate-conjugated antiserum to normal virus inclusions, the abnormal inclusions formed at 32.degree. C fluoresced.