Shoot axillary bud morphogenesis in kiwifruit (Actinidia deliciosa)

Abstract

The annual cycle of kiwifruit [Actinidia deliciosa (A. Chev.) C F. Liang et A. R. Ferguson var. deliciosa cv. Hayward] shoot axillary bud (first-order axillary bud. FOAB) morphogenesis is described. FOABs developed quickly with the majority of bud scales and leaf primordia present approx 125 d after budbreak (dab). Mature FOABs had, on average, 23.2 bud scales and leaf primordia. Most second-order axillary structures were also present approx. 125 dab. During the growing season, the second-order structures developed into second-order axillary buds (SOABs) or remained as simple, dome-shaped meristems (SDSMs). At maturity, nearly all FOABs had four SOABs and, on average. 124 SDSMs. Most SDSMs were fused to the subtending leaf primordia, but some SDSMs developed so that they were 'free' from the subtending leaf primordia. Third-order axillary meristems (third-order SDSMs) were observed in the axils of most SOABs, and, on average, there were 20.6 per FOAB. Our observations on the development of second-order axillary structures are consistent with evocation in kiwifruit occurring earlier than the generally-accepted time of late summer.