Graduate Thesis Or Dissertation
 

Relation of boron to cherry rosette disease in Oregon, and the possible implication in Oregon, and the possible implication of a virus

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  • A disease of sweet cherry (Prunus avium L.) known as "cherry rosette" has threatened production of cherries in Oregon. In 1961 this disease was observed in widely separated orchards. Rosette occurred in isolated trees or in spreading patterns, often from identified single trees or from one section of an orchard. A similar problem in 1953 is suspected to have been rosette. Rosette symptoms in cherry closely resembled those described for boron deficiency of stone fruits, but boron deficiency was not recognized as a problem of cherries in Oregon. Transmission by grafting, occurrence over a large area in trees on varying soils, and the spread in and among trees all suggested a virus as the causal agent of rosette. Boron spray trials were conducted in four commercial orchards. Leaf samples were collected monthly to determine the relation between boron levels and severity of rosette symptoms. In the spring the occurrence of rosette symptoms was correlated with a low boron content, but severity of symptoms did not vary directly with boron level. Foliar boron content increased from spring until midsummer, then levelled off and decreased in the fall. Analysis for boron in leaf samples collected in August rarily indicated boron deficiency in rosetted trees. The occurrence of rosette was not correlated with deviations from normal temperature and precipitation. However, a good positive correlation between winterstorms and the erratic occurrence of rosette was shown. Mahaleb and peach seedlings, graft inoculated with buds from rosetted trees, were used as intermediate hosts to permit mechanical transfer of a virus to herbaceous species. Direct mechanical transfer of viruses from cherries to herbaceous hosts is prevented by inhibitors. By using peach and mahaleb seedlings an unknown virus was isolated from two rosetted cherry trees and one rosetted peach tree. This unknown virus has not yet been implicated in a direct cause-and-effect relationship with rosette. No local-lesion assay host was found for the virus. The unknown virus induced a distinct epinasty of inoculated primary leaves of certain bean varieties, as did a cowpea strain of cucumber mosaic virus (CMV-CS). This and other evidence suggested that the unknown virus could be a strain of CMV. Serological tests with CMV antisera were inconclusive. A hypothesis has been presented that in cherry trees in soils with a marginal boron content, a delicate balance exists between boron supply and demand during budbreak and flowering. Storm damage to root systems probably reduces boron uptake, and a virus possibly could slow the flow of boron to sites with high rates of growth. A boron deficiency, no matter how induced, at a critical time in the development of leaves and flowers is the cause of cherry rosette. Boron sprays have corrected and prevented rosette in cherry trees. Recommendations were made for amount and time of application.
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