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Determination of Biological Aspects of Ganoderma boninense (Pat.) and their Pathogenic Potential on Oil Palm (Elaeis guineensis Jacq.) Seedlings
Abstract:
A total of five Ganoderma isolates from oil palm (Elaeis guineensis Jacq.) and coconut (Cocos nucifera L.) hosts were used in the determination of Ganoderma boninense based on monokaryotic mating compatibilities. Ganoderma specimens collected from both oil palm and coconut hosts fell into two types: (1) reddish brown with a varnished dorsal surface (“laccate”) represented by isolates EGB-01, CNL1, and CN-L2; and (2) dull brown non-varnished dorsal surface (“non-laccate”) represented by EG-NL and CN-NL. The isolate WD814 identified as G. boninense by the Forestry and Forest Products Research Institute (FFRRI) in Tsukuba, Japan was included as an outgroup sample.
The results of the study showed that based on sexual compatibilities of monosporus cultures obtained from a single fruitbody, the mating pattern of G. boninense was heterothallic and tetrapolar. The cultures fell into four distinct sex groups from which four monokaryon testers were successfully obtained. When tested for intergroup compatibilities, isolates CN-L1 and WD814 were compatible with EGB-01, whereas CN-L2, EG-NL, and CN-NL were not. Thus, monokaryon compatibility crosses confirmed that although EGB-01, CN-L1, and WD814 were from oil palm, coconut, and Livistona palm hosts, respectively, they all belonged to the same biological species.
The pathogenic potential of isolates from oil palm and coconut hosts were tested on oil palm seedlings over a 12-month period in glasshouse trials. Only EGB-01 and CN-L1 isolates were found to be pathogenic on oil palm seedlings, with both showing 100 percent infection. Totally no infection was established in palms inoculated with the non-G. boninense isolates EG-NL, CN-NL, and CN-L2. When infected seedlings were uprooted, the point of entry of G. boninense was found to be the larger primary root of the plant. A scanning electron micrograph (SEM) of a newly infected root showed that the fungi colonized the epidermis, cortex, endodermis, and lacunae, as well as plugged the xylem and phloem tissues. This indicated that fungal colonization was not restricted to any particular tissue. This study concluded firstly, more than one species of laccate Ganoderma can be found on coconut stumps. Secondly, G. boninense isolated from oil palm and coconut stumps were pathogenic on oil palms. Thirdly, the non-G. boninense specimens (EG-NL, CN-NL, and CN-L2) were pathogenic to oil palms.
