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This is the first investigation of the physiology of oil palm infected with Fusarium oxysporum f. sp. elaeidis, the causal organism of vascular wilt disease. Leaf stunting, a prominent symptom, was associated with prolonged mild water stress. Stunted leaves showed no decrease in the rate of transportation or photosynthesis per unit leaf area, and (despite a significant reduction in xylem diameter) a relatively small increase in vascular resistivity in the petiole. However, nonstunted leaves, that were formed before the pathogen became established, were severely and permanently water stressed. These water stressed leaves had a very high vascular resistivity in the petiole in spite of minimal reductions in xylem diameter, and minimal levels of visible vascular occlusion. It is possible that reductions in xylem diameter may lessen the occurrence of vascular embolisms, and in combination with the reduced leaf area may represent an adaptation to disease induced water stress. |
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