ANATOMICAL EFFECTS OF TOMATO RINGSPOT VIRUS IN VICIA FABA

spot. The virus used in this study (O.S.C.-644) was isolated from cucumber by McWhorter and has been determined serologically by Price to be a strain of tomato ringspot virus which is common in the Pacific Northwest on a wide variety of hosts. It has been maintained for six years by serial transfer from seedling to seedling of Vicia faba. The type strain of tomato ringspot virus, and also most strains of tobacco ringspot virus, are usually symptomless in this host. The cucumber strain, however, produces local lesions followed by a progressive necrosis of the stems and roots that results in the death of the plant. Other related viruses under investigation at this laboratory produce similar symptoms in the shoots of V. faba seedlings but do not induce necrosis at the base of the stem or in the roots. Also, the plants infected with these viruses later produce new shoots that are symptomless. This study was initiated to determine why plants infected with the cucumber strain of tomato ringspot virus seldom show this type of recovery. MATERIALS AND METHODS.-All seedlings were grown in the greenhouse in 6-in. pots with four to six seedlings in each. At least one plant in each pot was left as a control for each series of inoculations. Seedlings were mechanically inoculated on the upper surfaces of both leaflets of either the first or the second foliage leaf at the time of leaf expansion. The progress of necrosis was determined from free-hand sections of living material and from paraffin sections of fixed material. Stems, stem tips, leaves and roots were fixed in Randolph's solution, and root tips were fixed in Navashin's solution. Various modifications of the tertiary butyl alcohol-paraffin oil technique were used for dehydration and embedding. The embedded material was soaked in water at 380-400C. for 1-10 days before sectioning. Most sections were stained progressively with safranin and iron haematoxylin.