Characterization of Paecilomyces dactyletromorphus of gummosis disease on Albizia saman and its in-vitro fungicide evaluation

Albizia saman (Jacq) Merr is a native species from northern South America and Central America, cultivated and naturalized throughout the tropics. The plant was initially planted in Malaysia and later introduced to urban areas in the 1900s. Over the past years, a problem gummosis disease followed by the gradual tree failure of the affected trees has been observed in various parts of the urban environment in Malaysia. A. Saman showed gummosis symptoms, which were observed and investigated. The obvious symptoms of the infected A. saman trees are trunk discoloration, exudation of gummosis from the infected area, crusty exudate when dry, sap-feeding beetle, abnormal cavities on the trunk, cracked, sunken, and splits on the bark. This study attempts to explore the causal agents (pathogens) that cause the gummosis disease of A. saman. The studies are conducted to assess the tree health of A. saman in urban areas by identifying the pathogen that causes the symptoms, testing out the pathogenicity, and determining the best fungicide to control the disease. Isolation of fungi from gummosis and pest samples of affected raintrees revealed one fungal isolate o be the most dominantly and consistently isolated fungus. The causal agent of gummosis disease in the rain trees was identified using a DNA sequence-based method (ITS and β-tubulin) and morphology identification by scanning electron microscope (SEM) microscope and a compound microscope. The results show that Paecilomyces dactylethromorphus was the causal agent and fulfilled Koch’s postulates through a pathogenicity test. The result of the pathogenicity test revealed that there was a similarity in symptoms that arise between artificial inoculation and natural symptoms in the field. The effects of incorporating different concentrations (0.125%, 0.250%, 0.50%, 1.00%, and 2.00%) of each of the five fungicides (dimethomorph, thiram, copper hydroxide, mancozeb, and prochloraz manganese chloride) in 2% PDA medium were tested in vitro at the laboratory for 7 days and have shown that prochloraz manganese chloride fungicide with a concentration of 1.0% and 2.0% caused total inhibition of Paecilomyces growth. From this study, the susceptibility of fungal infections was due to injuries from anthropogenic and natural causes, and the application of fungicide of thiram mixture at 2.0 % can help control the disease at the field level.

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