SENSITIVITY OF BROCCOLI INFLORESCENCE DEVELOPMENT TO
HIGH TEMPERATURE.
Thomas Bjorkman and Karen Pearson, Department of Horticultural
Sciences, NYSAES, Cornell University, Geneva, NY 14456
Production of broccoli in areas where summer temperatures
exceed 30C is difficult because the head may not form
properly. The high temperature causes and unevenness
in the head due to widely differing sizes of buds.
The sensitive stage of development was determined
for the early-maturing variety Galaxy by exposing it
to 1 week at 36C at varying developmental stages, and
subsequently analyzing the head structure. The injury
is a cessation of bud enlargement during the high temperature
exposure. There is no corresponding cessation of bud
initiation at the apex. The pattern of injury is consistent
with susceptibility over a relatively small range of
bud development: even with a 1-week exposure, only
about 1/3 of the buds will be affected. The plants
most developmental stage at this sensitive period still
appears vegetative, but the youngest leaves are just
beginning to reorient as a consequence of the reduced
stem elongation rate. The meristem is less than 1
mm wide, and scanning electron micrographs show floral
primordia just forming, still subtended by leaf primordia.
The injury is fully expressed when the head is first
exposed (approx 10 mm wide), though it becomes more
apparent as the head matures. The buds that were delayed
in development by the high temperature developed into
fertile flowers, albeit about a week late.
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