Butt rot

Butt rot or 'top rot' of pineapple can be serious on pineapple 'seed materials' and occurs wherever pineapple is grown (Rohrbach, 1983). The causal fungus, C. paradoxa, is widespread in the tropics on pineapple, coconut and other palms, sugar cane as 'pineapple disease', cacao as 'pod rot', and banana as 'black-head disease' on rhizomes, suckers and roots, and as 'stem-end rot' on fruit (Dade, 1928).

The symptoms of butt rot are a soft rot and blackening of the basal portion of the stem tissue of vegetative seed material (Fig. 9.8). If infected seed material is kept wet, as in a pile of crowns, the infection may progress to rot the entire seed piece (stem and leaves) or even the entire pile. Severely rotted seed material is normally discarded prior to planting. Slightly to moderately infected seed material may be planted, but growth will be slow and plants will be stunted, due to loss of stem tissue, which contains carbohydrate reserves and the initial roots.

Fig. 9.8. Cross-section of crown showing pineapple butt rot caused by Chalara paradoxa and the loss of tissues from which adventitious roots arise.

When uncured or untreated seed material is planted in soils with high inoculum levels of C. paradoxa, butt rot levels may reach 100%. Inoculum levels in pineapple soils in Hawaii varied from an average of 2630 propagules g-1 following field preparation to 280 propagules g-1 of soil at the end of the crop cycle. At planting, inoculum levels varied by field from a high of 12,969 to as low as 31 propagules g-1 of soil (Rashid, 1975).

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