Promotion of flowering in potted Piceaengelmannii (Perry) grafts: effects of heat, drought, gibberellin A4/7, and their timing

Abstract

Young, potted grafts ofPiceaengelmannii were moved into a 30:20 °C (day:night) heated polyethylene house at different stages of lateral shoot elongation; and there they were subjected to low, moderate, or severe drought stress with and without branch applications of gibberellin A4/7 (GA4/7). The critical time for promoting flowering by high temperature was the late stage of slow shoot elongation, whereas for drought it was during early and rapid shoot growth. Each treatment inhibited flowering at the time the other was maximally effective and the effective treatment period for GA4/7 appeared to include that both for high temperature and drought. In contrast to drought, optimally timed heat treatment did not retard shoot elongation, nor did it result in a decreased needle water potential relative to well-watered grafts outdoors. It appears that heat and drought promote flowering through different mechanisms, albeit mechanisms which may be mediated, at least in part, through their influence on gibberellin metabolism. Advantages of indoor-potted orchards over conventional soil-based orchards for accelerating the breeding and production of genetically improved P. engelmannii seeds are discussed.