Defoliation alters spring growth flush characteristics and inhibits flowering in Protea cv. Carnival

Abstract

Inflorescence initiation in Protea cv. Carnival ( P. compacta R. Br.×P. neriifolia R. Br.) starts at spring budbreak, and production of involucral bracts occurs concurrently with spring flush elongation. The presence of mature leaves on an over-wintering shoot is essential for inflorescence initiation on the spring growth flush of ‘Carnival’ indicating that conditions prevailing during winter, whether environmental or intra-plant factors, are conducive to flowering. Total defoliation applied 40 days before spring budbreak or earlier prevented flowering, and reduced the stem length and number of leaves on the spring growth flush. Later defoliation had a less marked effect on spring flush characteristics, and all shoots initiated flowers. Early defoliation prevented flowering either directly by a reduction in available carbohydrates or removal of photoperiod and temperature perceptive tissues, or indirectly by the resultant production of a weaker spring flush. Shoots are in the induced state and committed to flowering 6–7 weeks before inflorescence initiation begins. The induced state is retained for a period and then gradually lost.