PNG Oil Palm Research Association, PO Box 36, Alotau, Milne Bay Province, Papua New Guinea.

Background and objectives
Ganoderma boninense Pat., a member of a family of wood-rotting basidiomycetes, is the causal agent of basal stem rot in oil palm plantations in Papua New Guinea (PNG). The disease has a long history in south-east Asia [1] and has only recently been found to occur in PNG. Disease incidence is currently low (<1%) and not considered a threat to the industry. However, studies on Ganoderma populations in oil palm plantations in Malaysia [2,3] indicate that the isolates from each palm are genetically distinct and therefore could not have arisen from vegetative spread of the fungus from palm to palm. Thus, basidiospores may play a more significant role in the epidemiology of the disease than previously thought. If this is found to be so, then it is expected that disease incidence will increase in successive plantings of oil palm.

Investigations into basal stem rot in Papua New Guinea are focused on determining the role of the basidiospore in the spread of the disease. This requires a basic understanding of the pathogen and its variability.

Results and conclusions
The mating system of G. boninense was found to be heterothallic tetrapolar. Crossing of single-spore isolates from different fruiting bodies resulted in dikaryon formation in all cases, indicating that multiple mating type alleles are present in the population on oil palm. This reinforces the idea of disease spread by spores but it is not known to what extent sexual recombination occurs to yield new mating type alleles. Mycelial incompatibility was found to occur between sibling monokaryons and dikaryons, with intensity of reactions decreasing with increasing relatedness. Dikaryotization of monokaryons was found to occur readily (100%) between unrelated monokaryons/dikaryons and approximately 50% for related dikaryons.

The mating system of Ganoderma has been shown to be complex and restricts inbreeding. Vegetative compatibility studies indicate that the dikaryon resists further nuclei exchange, allowing greater diversity within the population. Work is continuing in this area.

1. Turner PD, 1981. Oil palm Diseases and Disorders. Oxford: Oxford University Press.
2. Miller RNG et al. 1994. Understanding Ganoderma Populations in Oil Palm. Workshop on Perennial Crop Diseases Caused by Ganoderma. Serdang, Malaysia: UPM.
3. Darus A et al. (1996). Spread of Ganoderma boninense and vegetative compatibility studies of single field palm isolates. Proceedings of the PORIM International Palm Oil Congress, Kuala Lumpur, Malaysia.