Fusarium wilt of oil palm I. Possible causes of stunting

Abstract

In West Africa the most serious disease of oil palm (Elaeis guineensis) is vascular wilt caused by Fusarium oxysporum Schl. f.sp. elaeidis. Although severe stunting of leaves has frequently been reported in this disease and has been assumed to be a result of disease induced water stress, this is the first investigation of the mechanisms and possible causes of this symptom. In diseased palms stunting was due to a large (up to 95%) decrease in the size of both the petiole and leaf lamina, which were almost entirely caused by a reduction in cell division, rather than cell size. When uninoculated plants were exposed to drought there was a reduction in leaf number but not leaf size. However, the application of an inhibitor of gibberellin synthesis (Paclobutrazol) to uninfected palms resulted in very similar symptoms which were also due to a reduction in cell division. The application of gibberellin to both infected and uninfected palms caused an increase in petiole length, by an increase in cell division, but had no effect of the size of leaf lamina. These results provide circumstantial evidence that stunting in diseased palms is not caused by water stress and, at least in part, is the result of changes in the level or activity of host gibberellin.