Apr. 1933 
Peach Rosette^ an Infectious Mosaic 
311 
peach seedling showed rosette in all new growth (PI. 5, A). Peach 
seedlings into which healthy plum buds were inserted in 1921 showed no 
symptoms of rosette in the new growth of 1922. 
This indicates that the casual entity of rosette may readily be trans¬ 
mitted from peach to wild plum, and from wild plum to peach. 
Rosette has also been transmitted from the wild Chickasaw plum to 
the Red June plum by means of infected buds. 
PnUM TO PEACH 
Experiment 7.—natural infection of a Maynard plum developed in 
an orchard on the station in the spring of 1920. By June 15, 1920, most 
of the lateral buds had grown into rosetted shoots from i to 3 inches 
long; and by August, 1920, this tree (PI. 6, B) had made very little new 
growth as compared with a near-by healthy plum tree (PI. 6, A). On 
June 18, 1920, buds from this rosetted plum tree were put into a healthy 
seedling peach tree in its second season’s growth. Buds from a healthy 
plum were put into another peach seedling to serve as a control. On 
August 18, 1920, it was observed that some of the rosetted Maynard 
plum buds put into the peach seedling had produced shoots several inches 
long. Below the point where the diseased buds were inserted the 
peach buds had developed rosetted shoots (PI. 6, C). The disease con¬ 
tinued to spread in this peach seedling during the rest of the season of 
1920, and when new growth started in the spring of 1921 this tree showed 
rosette in all parts. It died before midsummer. One of the control 
buds produced normal leaves (PI. 7, A) and the peach stock on which 
it was growing was alive and healthy in the fall of 1921 when it was 
removed to make room for other experimental work. 
This experiment indicates that rosette originating in the cultivated 
plum may be transmitted to the peach. 
PEACH TO MARIANNA PLUM 
Experiment 8.—On June 18, 1920, buds from the rosetted peach 
seedling described in experiment 4 were put into a healthy Marianna 
plum branch, near the base of the tree. One bud started growth within 
two weeks and produced a rosetted shoot (PI. 7, B) with larger leaves 
and longer intemodal growth than rosetted shoots on peach stocks. No 
signs of rosette appeared on the Marianna stock during the summer of 
1920. After becoming dormant in the fall of 1920, this Marianna plum 
was transplanted to a large pot and placed in the greenhouse. In the 
spring of 1921 the peach shoot developed rosetted leaves, but continued 
to grow throughout the summer. The Marianna plum stock developed 
normal leaves on all of its branches, which grew rapidly throughout the 
summer. This Marianna plum (PI. 7, C) had been under observation 
in the greenhouse during the winter, and up to May i, 1922, it showed 
no symptoms of rosette. The rosetted peach shoot continued to grow 
slowly. When rosetted peach buds were put into a susceptible host, 
as peach, apricot, or ordinary cultivated plums, they died within 12 
months. On the resistant Marianna plum stock the rosetted peach bud 
grew into a shoot which at the time this paper was written had lived for 
22 months. This indicated that the resistant stock exerted a marked 
influence on the virulence of the causal entity of rosette in the peach 
scion. 
