Abstract
Abstract does not appear. First page follows. About a quarter of a century before virus diseases as such began to be recognized, evidence of graft transmission of a chlorosis of the rose was recorded in France (12)4. However, mosaic as a disease of importance in rose culture did not attract attention until about 1928 (14). Mosaic then for several years excited an unusual amount of comment and controversy (7),(8),(18) which has been only partially justified by more extensive observations and experiments (7), (13), (17). It is now apparent, at any rate, that the rose may be affected by virus diseases of some importance and may serve as a potential source of virus for other plants (10). The material presented in this paper relates to the mosaic type of disease only. The necrotic diseases reported from the eastern United States (2) and abroad (4), (5) have not been found in California. Symptoms As early as 1933, evidence began to appear in this work indicating that not one mosaic disease occurs among the cultivated roses but several. Since some of these were not recognized as distinct until recently, it will not be possible to treat them separately throughout this paper. For convenience these will be designated as “rose mosaic 1,” “rose mosaic 2,” and “rose mosaic 3,” and the corresponding viruses distinguished by their respective numbers. In roses grown out of doors, lime-induced chlorosis without malformation is rather common, notably in the Santa Clara Valley. In such cases the leaf blade becomes uniformly yellow rather than mottled. This may obscure or inhibit development of symptoms of the mosaic diseases and may in some cases be confused with them. Diagnosis in the field is also complicated very frequently by insect injury (7), particularly that produced by leafhoppers. Types of variegation are encountered occasionally, which appear to be entirely genetic in origin. Scions of one such rose (fig. 3, A) were grafted on Rosa odorata and kept under observation for several years.
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