Investigating optimal site conditions for flower bud production inEucalyptus smithiiorchards in South Africa

Abstract

Eucalyptus smithii is an important commercial forestry species in South Africa. The species' shy and erratic flowering tendencies hinder its genetic improvement and seed production. Breeders and seed producers are highly dependent on paclobutrazol (PBZ) applications for encouraging flower and seed production in E. smithii orchards. During the summer of 2003/04, an E. smithii flowering field trial series was established across a range of high elevation (1568-1828 m asl), cool temperate (13.8-15.5°C mean annual temperature (MAT)) commercial forestry sites in South Africa. The main objective was to investigate the interaction between PBZ and a range of climatic and landscape factors on E. smithii floral bud (umbel) production. The main aim was to define optimum environmental conditions for E. smithii umbel production and potential orchard establishment. In the fifth and sixth years after planting, 64% and 83% of the control (nil PBZ) grafted trees and 94% and 94% of PBZ-treated trees produced umbels. In the fifth year, PBZ application increased mean (across-site) umbel production per tree by 132%. Regardless of whether PBZ was applied or not, mean umbel production varied markedly across sites. In the absence of PBZ application, E. smithii test orchards located on south-west facing slopes in high elevation (>1550 m asl) areas at the lower end of the applied MAT range were generally the most productive on the basis of umbel crop. The study demonstrated that, through careful site selection, dependency on PBZ to achieve satisfactory umbel production in reproductively mature E. smithii trees may be substantially reduced. Within the elevation and MAT ranges applied in the trial series, E. smithii orchards situated in low positions in the landscape were at high risk of being severely damaged by frosts. ARTICLE HISTORY

Flowering acceleration in native Brazilian tree species for genetic conservation and breeding

“…In this study, we found that PBZ application induced early flowering and fruiting, in agreement with its effects on grafted Eucalyptus nitens (Gardner et al 2013), E. smithii (Gardner et al 2016), E. globulus (Hasan &Reid 1995), E. camaldulensis, andE. tereticornis (Varghese et al 2009) seedlings, confirming the efficacy of this growth regulator in accelerating the transition to adulthood in perennial tree species.…”

“…terebinthifoliusand J. mimosifolia produced flowers and fruits both outdoors and in the greenhouse, indicating that climatic conditions were favorable for the reproduction of these species. PBZ probably contributed to these results by decreasing GA concentrations (Zhang et al 2019) and increasing abscisic acid and cytokine concentrations in flower buds (Srivastav et al 2010, Gardner et al 2016, thereby redirecting the available resources to flower development (Yuceeret al 2003, Upreti et al 2014, Srilatha et al 2016.…”

“…Grafting and growth regulators can be used to induce early flowering in plants (Martínez-Fuentes et al 2013, Gardner et al 2016, Zhang et al 2016, Soumya et al 2017, Bindu et al 2018. Paclobutrazol (PBZ) [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pentan-3-ol] is a triazole fungicide with growth regulatory properties (Soumya et al 2017).…”

“…Paclobutrazol (PBZ) [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pentan-3-ol] is a triazole fungicide with growth regulatory properties (Soumya et al 2017). It has been shown to reduce growth (Hasan & Reid 1995), increase flowering (Gardner et al 2016), and shorten generation cycles (Wei et al 2018). PBZ acts by inhibiting the synthesis of gibberellins (GAs), a family of growth hormones (Kishore et al 2015).…”

Modulation of the initial growth of Eucalyptus clones using paclobutrazol: when smaller is better

“…Changes promoted by PBZ depend on species, variety and plant development stage as well as PBZ concentration and application method (Silva and Faria Jr, 2011). Regarding Eucalyptus cultivation, PBZ shortens the juvenile stage and stimulates the reproductive phase, resulting in early flowering (initiation of flower buds) (Moraes et al,2014;Gardner et al, 2016;Klocko et al, 2016;Potts et al, 2008). The effects of PBZ on Eucalyptus growth were first reported in the 1990s (Willians et al, 1999;Griffin et al, 1993).…”