Apple mosaic

Abstract does not appear. First page follows.

An infectious variegation of apple foliage seems to have been recognized by Vibert in France as early as 1835.3 Earlier reports from the northeastern United States recently reviewed⁽¹⁾4 indicate that mosaic of apple is general in that area, though seldom if ever destructive. Mottled apple foliage has been noted in the State of Washington,⁽³⁾,⁽⁴⁾ some of which may represent the disease under consideration here. A mosaic type of disease which is probably distinct has been found on an ornamental apple in Kentucky.⁽⁹⁾ A report⁽²⁾ of apple mosaic has appeared from Bulgaria, but the illustrations accompanying it are more characteristic of noninfectious types of chlorosis.

Specimens of mosaic in the variety Ranier were received from Paradise, California, in June, 1932. The trees had been purchased from a nursery in the State of Washington about five years earlier. In August, 1936, a single tree of Smith Cider obtained from a local nursery was found affected in a garden at Berkeley. Some of the affected trees or branches in the orchard at Paradise show, in addition to the direct loss of functional leaf area, a sparseness of foliage and reduction of terminal growth which seems to be chargeable to the mosaic disease.

Plants Affected and Symptoms

Heretofore the disease has apparently been known only on the cultivated apple, Pyrus malus. On this plant, the typical symptoms have been amply illustrated⁽⁶⁾,⁽¹⁾ (fig. 1). In addition to the symptoms commonly seen on the apple, there occasionally appears a complete chlorosis of the larger veins (vein clearing) while the remainder of the leaf retains the normal form and color.⁽⁶⁾ Of particular interest is the tendency of the chlorotic areas to be entirely killed both at Paradise and Berkeley during the summer months of intense sunlight.