Physiology of Plant Virus Diseases

Abstract

In the past a great deal of work has been done on the respiration of virus-diseased plants, much of it with tobacco mosaic virus. The results, however, have been confusing and often contradictory, chiefly because there are so many variable factors not taken into account by the earlier workers. Owen (1955b) points out that the variability in respiration rate between comparable leaves of similarly treated plants is so great, even when plants are selected for uniformity of size and appearance, that many replications are necessary to establish unequivocally the nature and magnitude of the effect of infection. Owen’s experiments on the respiration rates of mosaic-infected tobacco leaves show that these rates can be higher or lower than, or identical with, those of healthy leaves depending upon: (a) the time after inoculation; (b) the physiological state of the plants; (c) the environmental conditions during growth; (d) the leaves chosen; or (e) the mode of expression of the results. In future work on respiration rates of virus-diseased plants, it will be necessary to take these facts into consideration and also to apply adequate statistical tests of significance to any differences obtained.