Browsing by Author "Daranagama, D. A. D. A"

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    Identification and biocontrol of causative agents of Leaf Fall Disease (LFD) in Hevea brasiliensis (rubber) trees of Sri Lanka
    (Faculty of Science, University of Kelaniya Sri Lanka, 2024) Wijayarathna, W. A. L.; Daranagama, D. A. D. A
    Leaf Fall Disease (LFD) is among the most devastating threats to natural rubber (Hevea brasiliensis) production. The unusual off-season leaf shedding caused by this disease has led to a 30% reduction in rubber production in Sri Lanka in 2019. Despite its significant impact, the exact pathogen responsible for the recent LFD outbreaks has not been conclusively identified. This study aimed to determine the causative agent(s) of LFD in rubber and to develop effective biocontrol methods to manage and control the disease. Diseased leaf samples were collected from rubber plantations in Kalutara and Colombo, and pathogens were isolated on Potato Dextrose Agar (PDA) using single spore isolation. The morphological characteristics of each isolate were observed after 10 days of incubation under aseptic conditions. Pathogenicity tests were conducted by reinoculating isolated pathogens onto healthy attached and detached rubber leaves (RRIM-600 T1) at the same maturity stage, between copper brown and apple green colors, and Disease Index (DI) values were calculated for each leaf DNA was extracted using the modified CTAB (Cetryltrimethylammonium bromide) method, and combined analysis of ITS, β-TUB, and TEF-1α gene regions was used to reconstruct phylogenetic trees for the isolated pathogens. Selected pathogens were subjected to biocontrol experiments using Trichoderma atroviride and Daldinia eschscholtzii using the dual culture plate method. Percentage Inhibition of Radial Growth (PIRG%) was determined to assess the effectiveness of the biocontrol agents. The isolated pathogens exhibited diverse cultural and micro-morphological characteristics. Collectrotrichum siamense, Pseudopestalotiopsis simitheae, and Neopestalotiopsis saprophytica were identified as the causative agents of LFD in rubber in Sri Lanka. All isolates showed varying degrees of pathogenicity across different inoculation modes, with the highest DI value observed for leaves coinoculated with C. siamense and P. simitheae after wounding and P values from the one-way ANOVA reveal significant differences (p < 0.05) in lesion development among pathogens and reinoculation methods. D. eschscholtzii demonstrated effective control of both C. siamense and P. simitheae, achieving PIRG% values exceeding 50%. However, T. atroviride exhibited a mild ability to control only P. simitheae, with only two out of three replicates showing PIRG% values higher than 50%. It is recommended that continuous identification and control efforts, using various biocontrol methods, are carried out to protect rubber plantations and mitigate the economic losses associated with it. In conclusion, newly emerged LFD in rubber plantations is caused by C. siamense, N. saprophytica, and P. simitheae, while D. eschscholtzii is a potential biocontrol agent for managing the disease.