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Implementation of an early artificial inoculation test to screen oil palm progenies for their level of resistance and hypothesis on natural infection : Ganoderma disease of the oil palm

Breton F., Miranti R., Lubis Z., Hayun Z., Setiawati U., Flori A., Nelson S., Durand-Gasselin T., Jacquemard J.C., De Franqueville H.. 2009. In : 16th International Oil Palm Conference and Expopalma. Challenges in sustainable oil palm development, 22 to 25 September 2009, Cartegena de Indias, Colombia. Bogota : FEDEPALMA, p. 1-30. International Oil Palm Conference and Expopalma. 16, 2009-09-22/2009-09-25, Carthagène des Indes (Colombie).

Genetic resistance to basal stem rot (BSR) of oil palm is a major component of an integrated control strategy for BSR disease. Early detection of the level of resistance or susceptibility is of paramount importance for the breeding and sustainability of this crop particularly in Southeast Asia. A screening test of oil palm progenies has been developed and validated by using planting material from two Indonesian private companies - PT PP London Sumatra Indonesia (Lonsum) and PT Socfin Indonesia (Socfindo). This test was performed in the nursery, at the germinated seed stage, using a shade characterized by a light filtration of around 85%. Rubber wood blocks (RWBs) infected by Ganoderma boninense 12 weeks prior to inoculation were used as the inoculum source. The first disease symptoms appeared between 8 to 10 weeks after the nursery bags were inoculated and germinated seed planted. Analyses for each tested cross showed positive correlation between 16 and 28 weeks indicating that early selection is realistic and there is minimal interaction of disease susceptibility with time. These results were consistent and reproducible and no changes in the ranking were observed between external and internal symptoms recordings. Statistical analyses demonstrated significant variation between progenies and consistent ranking of progenies tested in independent trials. The analyses of the F values indicated that the kinetics of the screening test reached an acceptable level of discrimination 20 weeks after inoculation. Nursery results compared with field results, recorded in natural condition of infection, showed that with the test, no highly-susceptible progenies would have been planted. The major aim of this paper is to highlight the efficiency and the reproducibility of this early prenursery inoculation test which allows to screen now around 100 progenies per month. In parallel, the development of a melanised tough mycelium named stromatic-like structure has been observed in the lignified cavity at the base of infected palm; Root-Bol interface. Randomly field observations of the young and mature palm seem to demonstrate that the initial point of Ganoderma penetration is localised in this lignified area. No initial Ganoderma invasion of young palms by the fungus was observed at the peripheral area of this lignified cavity.

Mots-clés : elaeis guineensis; ganoderma; indonésie; ganoderma boninense

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