HIGH-TEMPERATURE ARREST OF INFLORESCENCE DEVELOPMENT IN BROCCOLI (BRASSICA-OLERACEA VAR. ITALICA L.)

High temperature causes unevenly-sized flower buds on broccoli inflore scences, This deformity limits production of broccoli to areas where s ummer temperatures rarely exceed 30 degrees C, The stage of developmen t sensitive to heat was determined by exposing plants of 'Galaxy' broc coli at varying developmental stages to 35 degrees C day temperature f or 1 week, and subsequently analysing the head structure, During the h igh temperature exposure, the development of certain flower buds was a rrested, 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, Meriste ms were affected only if heat was applied during inflorescence product ion or the floral initiation process, Shorter heat exposures produced little injury, and longer exposures were lethal. The plant's developme nt 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 prim ordia. The injury was fully expressed by the time the head was first e xposed (approximately 5-10 mm wide), though it became more apparent as the head matured, The buds that were delayed in development by the hi gh temperature developed into normal flowers.