Possible cause(s) of red leaf disease (RLD) of pineapple (
Ananas comosus
L.) in Ghana were examined through field observations, isolation of suspected organisms from roots of diseased plants, growing plants in potted steam-sterilised and unsterilised natural field soils. Others included detection of the pineapple closterovirus (PCV) from symptomatic and healthy pineapple leaves using tissue blot immunoassay (TBIA). Effects of soil moisture, soil fertility, sucker condition and light intensity on the disease were studied in pots while some factor combinations were studied in mini plots in the field. Diseased plants from the field had reduced root systems and had
Neosartorya fischeri
. Nematodes of the genera
Aphelenchus
,
Pratylenchus
and
Helicotylenchus
were recovered from roots and infrequently from the rind of the underground stem. Pineapple plants grown outdoors in steam-sterilised field soil reddened just as those grown in unsterilised soil. The PCV was detected in only 53% of all typically symptomatic leaves examined. All non-symptomatic leaves also tested positive for PCV. Plants grown from symptomatic suckers in a plant house with diffuse light intensity (7,440 lm m
-2) and at 29 °C, recovered from RLD within 6 months. These plants, however, reddened when grown outdoors with intense light (39,751 lm m
-2) at 30 °C. Significantly (P<0.05) lower disease levels were recorded on mini-plots optimally fertilised with NPK and maintained at high moisture than on low fertility, low moisture plots. In a further mini plot trial, plants grown with reduced light had lower disease levels than those grown with full light. Overall, these results show that soil biotic factors have no primary etiological role in RLD. The viral nature of the disease is also doubtful. Leaf reddening in pineapple could be a physiological response to environmental stresses.