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Abscission of Citrus Fruit and Ethylene Production by Clementine Tangerine Fruit Grafted onto Seedlings Infected with Stubborn Virus. E. O. Olson, Plant Pathologist, Crops Research Division, ARS, USDA, Indio, California 92201; Bruce Rogers(2), and G. K. Rasmussen(3). (2)Plant Physiologist, Crops Research Division, ARS, USDA, Pasadena, California 91109; (3)Plant Physiologist, Crops Research Division, ARS, USDA, Orlando, Florida 32803. Phytopathology 60:155-157. Accepted for publication 27 August 1969. DOI: 10.1094/Phyto-60-155.

We grafted twigs bearing immature, healthy fruit of six Citrus cultivars onto virus- infected seedlings with mottled-leaf symptoms of stubborn disease. Many fruit of Clementine tangerine, Pineapple orange, and Redblush grapefruit abscised within 5 months when grafted onto infected seedlings, but few abscised when grafted onto normal seedlings. Fruit of Eureka lemon, Rough lemon, and Rangpur lime did not abscise in a similar period even when grafted onto infected seedlings. Fruit of Clementine tangerines which abscised from infected seedlings averaged 1,100 ppb ethylene in their internal atmosphere; that of normal fruit averaged 100 ppb ethylene. More ethylene was produced by partly colored, abscised Clementine fruit from stubborn-affected seedlings than by freshly-picked green fruits from normal plants. Significant differences in ethylene production by foliage of normal and infected plants were not detected. The evidence, some circumstantial, supports the hypothesis that virus infection caused necrosis, which increased ethylene production, which caused the premature abscission of fruit of susceptible cultivars.