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Show 1938] The Blood, Watson: Tobacco Mosaic Virus No. I in Datura 17 development of systemic symptoms on Datura meteloides inoculated with the tobacco mosaic virus no. 1 The early observations of the development of the systemic virus on D. meteloides inoculated with local collections of the tomato mosaic virus raised a question regarding the relationship of such viruses to Johnson's tobacco virus no. 1. Inoculations were made at various times of the year on D. meteloides with collections of tobacco mosaic virus no. 1, obtained from various sources. The inoculations were all made, and the plants incubated, in a greenhouse with temperatures fluctuating as noted above. The develop ment of the systemic virus on D. meteloides plants inoculated with common tobacco mosaic has occurred at all seasons of the year, but in some experi ments none of the plants inoculated developed systemic virus symptoms while in other experiments systemic virus symptoms appeared on as high as 5 percent of the plants inoculated. In those cases the sequence of symptorna logical development was the same as in the experiments with the tomato mosaic virus. Nearly half of the plants inoculated were eliminated because the plants were killed by the severeness of the primary necrosis before they produced secondary shoots. In only a few cases did the streaks advance far enough to produce the secondary symptoms of necrosis-i. e., streaking of secondary shoots-before the plants were discarded to make room for other experiments. Had it been possible to hold the infected plants longer, a greater percentage of them might have produced symptoms of the systemic virus. All plants in which secondary necrosis developed on the new young axillary shoots either developed systemic symptoms or were killed by the severity of the streaking virus. Factors favoring development of systemic virus The factors determining the number of plants that develop systemic are unknown at present. Observations made on experiments con ducted during the several seasons of the year indicate a possible correlation between the number of cases of systemic development and the temperature and light intensity to which the plants are subjected during the development of the virus. Systemic development appears more frequently during summer months of high temperature and long days. The longer infected Datura plants survive, following inoculations with the tobacco mosaic virus, the greater appears to be the chance for the appearance of systemic symptoms. Since the streaks enlarge slowly, the longer the time allowed for such en the largement greater is the possibility of a secondary shoot becoming in vaded by the virus. In every case the systemic infection has appeared follow ing the invasion of a secondary shoot by the tobacco mosaic virus. symptoms Comparison of the tomato mosaic, tobacco mosaic and systemic viruses Host range. Capsicum annuum, Datum stramonium, Nicotiana glutinosa, N. tabacum, N. rustica, N. tabacum. N. aluiinosa, Solanum melonaena, S. pyra canthos, S. nigrum, S. cilia tum, Hvoscyanus niger, and Nicandra physalodes, referred to in literature as susceptible to -tobacco mosaic virus no. 1, were observed to be hosts of the tobacco mosaic virus no. 1, of the tobacco mosaic and of the systemic virus. virus, The symptoms developed by all viruses were similar to those mentioned in the literature as characteristic of tobacco virus no. 1. Datura meteloides, D. metel, D. discolor, D. fastuosa, N. iexana, S. bterocaulon, S. luteum. S. sisvmbriiolium-, S. citrullifolium. and S. ameri canum, not recorded in literature as hosts, were also found to be host plants " » .., , , " , " ./:J) , _ .J .J |
