Ethylene-releasing agents such as ethephon
(2-chloroethylphosphonic acid) are used widely to induce
flowering in pineapples (Ananas comosus (L.) Merrill).
However, ethephon treatment is less reliable in
summer, particularly if plants are treated on abnormally
hot days. [14C]ethephon was used to follow uptake and
translocation in leaf tissues. Up to 30% of the ethephon
entered the leaf within 4 h, and up to 60% by 24 h.
Uptake was dramatically modified by temperature, relative
humidity, solution pH, and the surface on which
solution droplets were placed. Entry occurred across the
leaf cuticle and probably also by way of stomatal pores,
and label was recovered at all depths within the leaf. 14C
label entered more rapidly through the abaxial epidermis
than through the adaxial epidermis. Low-volume spray
applications to whole plants resulted in rapidly drying
droplets mainly on the adaxial, distal epidermis and were
rather ineffective at inducing flowering, possibly because
little ethephon or ethylene reaches the shoot apex. Highvolume
sprays may facilitate ethephon entry because solution
accumulates in leaf axils and hence remains in
prolonged contact with abaxial epidermis of leaf bases
close to the shoot apex. When poured into the center of
the plant, 20% of a normal commercial ethephon dose
induced full flowering even under adverse temperatures.
It is suggested that high-volume evening spraying and
avoidance of hot days may reduce the incidence of flowering
failure.