Identification and characterization of dieback syndrome in Camelliasinensis (TRI 2025)

Abstract

The disease has been reported in the tea cultivar TRI 2025, grown in the upcountry since 1989 (Nethaniel, 1999). Preliminary observations from different locations where the disease has already been reported showed pathological affiliations instead of a physiological disorder or agronomical reasons. During the eight months under investigation in the Nuwara Eliya Estate, the affected area expandedby 129.75 m2. A distinctive increase in the rate of spread was observed during dry seasons. Asignificant relationship between the spread of the disease and climatic stress was found. The rate ofspread of the disease was higher with low relative humidity and rainfall. The expansion of the patch followed the direction of the wind with an indication of an airborne disease. Phylloplane microflora of TRI 2025 between healthy and diseased plants, the soils, which they are grown, collected from diseased and healthy areas found to have no significant difference. However, Pantoea agglomerans (Beijerinck) (Gavini et al., 1989), a Gram negative rod was solely and repeatedly isolated on nutrient agar, from the xylem sap of diseased plants. The sap of visually healthy plants, of the same cultivar upon prolonged incubation developed few colonies of the same bacterium. The bacterium was also isolated from dew collected from leaves of the diseased plants. The isolate was confirmed by the International Mycological Institute (IMI) in the United Kingdom (Offord, 2003). Four experimental sets of plants used to demonstrate Koch’s postulates, using mature tea bushes (Nuwara Eliya and St. Coomb’s), young plants and tomato seedlings. None of the sets met with conclusive results. Stem section analysis of the cultivar showed a significant xylem blocking in diseased plants, which increased in numbers with the severity of symptoms. P. agglomerans (Beijerinck) (Gavini et al., 1989), produce high-molecular-weight extra-cellular polysaccharides (Balows et al., 1992) and some strains are ice-nucleae active causing frost damage (Pajand,2005). Under the evidences the dieback in TRI 2025 can be classified as a stress driven relationship between a stressed plant and an opportunist.