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About 3% of banana seedlings derived from tissue culture(TC) of
Philippinose banana cultivar "Umalag" produced etiologically
unknown new disease so-called "banana red spot" inducing
redish brown spots on leaf blades, midribes and petioles. The
disease did not occur in other banana cultivars. Diagnostic
examination by means of tissue isolation, viral inoculation
of indicator plants, paraffin sectioning, tissue clearing, and
electronmicro- scopy revealed that no fungus, bacterium,
mycoplasms, virus or inclusions were found to be associated.
Inoculation of healthy banana seedlings with diseased
materials through mechanical, puncture, inarching, and
core inoculation methods failed to transmit the disease.
The disease occurred sporadically in the banana orchards
established with TC-seedling only, and it was not spread from
the diseased to the adjacent healthy plants. The disease was
transmitted only through vegetatively propagated seedlings,
i.e. suckers from diseased plants and TC-seedlings derived
from diseased rhizomes developed the disease. It was
assumed that the disease was caused by gene defect due to
muta- tion occurring during tissue-culture propagation of
Umalag cul- tivar. The xylem vessels of diseased plants
were generally plugged with gel matrix. Abnormal
metabolic products, and spherial bodies stained by phenolic-
affinitive dyes, were formed in the mesophyll cells and the
other parenchyma cells, some of which eventurely became
necrotic due to cytoplasm coagulation. The light affected
disease development; disease development was considerably
prohibited by low light intensity.
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