Impact of genotype and parent origin on the efficacy and optimal timing of GA4/7 stem injections in a lodgepole pine seed orchard

Simon W Bockstette,Barb R Thomas

doi:10.1007/s11056-019-09733-w

Abstract

Seed orchards play a critical role in reforestation, but often struggle to consistently produce enough seed. A mixture of the less polar gibberellins, GA4 and GA7, has been shown to promote flowering in Pinaceae species, but the responses vary significantly based on species, genotype and provenance, application method, timing and dosage. Previous studies with lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) suggest that the response to exogenous GA4/7 varied among genotypes. Gibberellins also play a critical role in seed development and germination but it remains unclear how exogenous GA4/7 will affect seed quality. We used 25 lodgepole pine genotypes in a commercial seed orchard in Alberta, Canada to explore the impact of genotype and geographic origin on the efficacy and optimal timing of GA4/7 stem injections to promote female cone bud initiation, cones and seed production. Overall, we found that GA4/7 stem injections promoted female conelets in 40% of genotypes included in this study. For these 10 genotypes, we found that the latitude of their provenance was positively correlated with later effective application times. Of the remaining 15 genotypes, five were hypersensitive to exogenous GA4/7 showing needle discolouration and loss, and 10 genotypes showed no response. In general, stem-injected GA4/7 did not affect the number of seeds per cone while two genotypes showed a reduced seed yield and one genotype showed increased seed yield per cone. Seed weights were not affected by the stem-injected GA4/7, while the July application date resulted in higher germination rates compared to control trees.

Highlights

Seed orchards play a critical role in supplying high-quality seed for reforestation, but often struggle to consistently produce enough seed (Giertych 1987; Eriksson et al 1998)
Research conducted in the late 1970s and 80s showed that in many conifers, cone bud initiation can be promoted through the application of exogenous gibberellins (GA) and other plant growth regulators (Ross and Pharis 1976; Pharis et al 1980, 1987; Owens and Blake 1985; Bonnet-Masimbert 1987)
For the 10 remaining genotypes that showed an increase in female conelet production in response to the exogenous GA4/7, the effective application times represented the full range of treatments (i.e. June–August) (Table 3)

Summary

Introduction

Seed orchards play a critical role in supplying high-quality seed for reforestation, but often struggle to consistently produce enough seed (Giertych 1987; Eriksson et al 1998). A mixture of the less polar gibberellins, GA4 and GA7, has been shown to promote flowering and thereby enhance conelet production in Pinaceae species, but the responses can vary significantly based on species, genotype and provenance, as well as application method, timing and dosage (Eriksson et al 1998; Zhao et al 2011). Wheeler et al (1980) found that exogenous GA4/7, applied as a spray or droplets, can be used to enhance female conelet production in lodgepole pine In a recent study with only two genotypes in a lodgepole pine seed orchard, GA4/7 stem injections promoted female cone production in one of the genotypes, while the other genotype showed no response (Kong et al 2018). It is reasonable to consider that the optimal timing of any G A4/7 treatment will vary among seed orchard trees based on the geographic origin of the parent tree

Methods

Results

Conclusion