Characterization of parameters for the development of an early screening test for basal stem rot tolerance in oil palm progenies

Basal stem rot (BSR) of oil palm (Elaeis guineensis Jacq.) is caused by Ganoderma boninense, and is one of the most commercially significant devastating diseases in Southeast Asia. So far, cultural practices, combined to some extent with biological control, have been considered as the best approach for controlling the disease. However, in recent years, sources of genetic resistance and susceptibility have been identified in field trials, leading to the consideration of a genetic approach as an integrated component in controlling the disease. To develop this approach, an early screening test at the nursery or prenursery stage is needed, based on artificial inoculation and correlated with field observations. The success of nursery seedling artificial inoculation relies on a set of parameters such as the aggressiveness of G. boninense isolates, the incubation period of pre-infected rubber wood blocks (RWB), the ratio between the size of pre-infected RWBs and the volume of soil for infection, and the quality of nursery or prenursery shade. When this set of parameters was optimized, disease symptoms were observed 3 months after the inoculation of germinated seeds. This avoided the transfer of seedlings from the prenursery to the main nursery, minimized transplanting shock and root damage, and also reduced the time taken for the screening test and the nursery area required. This early inoculation enabled the discrimination of isolates according to their aggressiveness, expressed by the quantification of external and internal disease symptoms and by using a standardized scoring scale. Development of this method will lead to the selection of isolates to be used in screening for resistance or tolerance to BSR.