Overhead irrigation increased winter chilling and floral bud production in Eucalyptus nitens

  • Robin AW Gardner
  • Isa Bertling
  • Michael J Savage

Abstract

Eucalyptus nitens requires a sufficiently cold winter to produce flower buds. In areas in South Africa where E. nitens commercial plantations as well as breeding and production seed orchards are located, winter chilling is often insufficient for floral bud initiation. Hence, under such conditions, E. nitens floral bud and seed crops are poor and inconsistent. The local industry is almost entirely dependent on paclobutrazol (PBZ) applications for encouraging flowering in E. nitens seed orchards. Between 2008 and 2010, an experiment was conducted to investigate the potential of overhead irrigation (sprinkling) as a means of supplementing winter chilling to improve floral bud production in E. nitens. The treatments included three levels of sprinkling (nil, 10 weeks and 16 weeks duration), two levels of PBZ (nil, 0.025 g a.i. per mm basal stem circumference) and two grafted clones (prolific flowerer and shy-flowerer). Sprinkling reduced E. nitens daytime bud temperatures by as much as 16.2 ºC on warm, dry winter days. In 2009 (cold winter) and 2010 (warm winter), sprinkling increased chilling accumulation by 44% and 72% (nil versus maximum sprinkling), respectively. In 2009, in the absence of PBZ, sprinkling resulted in a higher percentage of trees of either clone producing umbels (flower buds) compared with the control. In the warmer 2010 winter, sprinkling again increased flowering, with the number of flowering shoots and umbels per tree being significantly higher than the control at p < 0.05. In both 2009 and 2010, PBZ showed a strong additive effect to winter chilling on E. nitens floral bud production. The E. nitens clone  chilling  PBZ flowering interaction was complex and warrants more detailed investigation in future. Overhead sprinkling offers a practical method of supplementing winter chilling and improving floral bud production in high-chill-requiring temperate eucalypt species such as E. nitens.

Keywords: chill modelling, evaporative cooling, global warming, insufficient chilling, paclobutrazol, seed orchard

Southern Forests 2013, 75(4): 199–212

Author Biographies

Robin AW Gardner
Institute for Commercial Forestry Research, PO Box 100281, Scottsville 3209, South Africa; Horticultural Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa
Isa Bertling
Horticultural Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa
Michael J Savage
Agro-meteorology, Soil-Plant-Atmosphere Research, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa
Published
2013-11-13
Section
Articles

Journal Identifiers


eISSN: 2070-2639
print ISSN: 2070-2620