Journal of Experimental Botany 49:101-106. 1998.
High temperature arrest of inflorescence development in
broccoli (Brassica
oleracea var. italica L.)
Thomas Björkman and Karen J. Pearson
Department of Horticultural Sciences, New York State Agricultural
Experiment
Station, Cornell University, Geneva, NY 14456
ABSTRACT High temperature causes unevenly-sized
flower buds on broccoli
inflorescences. This deformity limits production of broccoli to areas
where
summer temperatures rarely exceed 30°C. The stage of
development sensitive
to heat was determined by exposing plants of 'Galaxy' broccoli at
varying
developmental stages to 35 °C day temperature for 1 week, and
subsequently
analyzing the head structure. During the high temperature exposure, the
development of certain flower buds was arrested. There was no
corresponding
cessation of bud initiation at the apex. No injury resulted if heat was
applied before the reproductive induction, nor was there injury to
differentiated
flower buds. Meristems were affected only if heat was applied during
inflorescence
production or the floral initiation process. Shorter heat exposures
produced
little injury, and longer exposures were lethal. The plant's
development
at this sensitive period still appeared vegetative externally, but the
youngest leaves had just begun to reorientate as a consequence of the
reduced
stem elongation rate. The meristem was less than 1 mm wide, and floral
primordia were just forming, still subtended by leaf primordia. The
injury
was fully expressed by the time the head was first exposed (approx. 5
to
10 mm wide), though it became more apparent as the head matured. The
buds
that were delayed in development by the high temperature developed into
normal flowers.
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