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Basal and upper stem rot of oil palm is caused by the agaricomycete Ganoderma boninense. This study investigated the transmission of basal stem rot from Ganoderma‐infected oil palm stumps to young oil palm seedlings. Low seedling mortalities (2.5%) were observed in a field trial after 24 months, but G. boninense could be detected in the rachis, bole and roots of a significant proportion of seedlings that were outwardly healthy. A high level of genetic heterogeneity amongst G. boninense isolates within the trial area was revealed. Furthermore, germinated seedlings growing in close proximity to infected palms in a mature oil palm field contained multiple isolates of G. boninense indicating that colonization of roots by basidiospores and dikaryons, arising from mating between basidiospores, is a common occurrence in oil palm plantations. The probability that basidiospores are a direct source of inoculum in addition to diseased trunk tissue is discussed as a means of explaining the observed heterogeneity in populations of G. boninense on oil palm. Such a scenario presents challenges for the long‐term management of basal stem rot. [ABSTRACT FROM AUTHOR]

Ganoderma boninense (the causal agent of basal stem rot of oil palm in Papua New Guinea) has a tetrapolar mating system with multiple alleles. Investigations into the population structure of G. boninense , using interfertility between isolates as a marker, revealed that the population on oil palm was comprised predominantly of genetically distinct individuals, although a number of isolates were found to share single mating alleles. No direct hereditary relationship was found between isolates on neighbouring or spatially separated diseased palms, indicating that outcrossing had probably occurred over several generations in the founder population prior to colonization of oil palm. In this study, a total of 81 A and 83 B mating type alleles (factors) were detected with 18 allelic repeats at the A locus and 17 at the B locus. Alleles appeared to be randomly dispersed throughout the population in each study block, although there was a significantly (P < 0·01) higher proportion of allelic repeats between estates separated by several kilometres compared to within estates. This is the first study on the population structure of this species and confirms that sexual reproduction is a significant component of the epidemiology of this disease. [ABSTRACT FROM AUTHOR]