Effects of stem-injected gibberellins and 6-benzylaminopurine on phytohormone profiles and cone yield in two lodgepole pine genotypes

Abstract

Stem-injection of plant growth regulators into ramets of two lodgepole pine genotypes altered endogenous phytohormones and metabolites in long-shoot buds, and in one of the genotypes, dramatically increased female cone yield. Effects of exogenously applied gibberellins (GAs) and 6-benzylaminopurine (BA) on profiles of phytohormones and some of their metabolites relative to controls in long-shoot buds of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were analyzed during cone bud initiation and differentiation. Differential responses in phytohormones and in cone yield were observed in ramets of the two tested genotypes (478 and 276) to stem-injected mixtures of GA4 and GA7 (GA4/7) and /or BA. Injected GA4/7 affected bud concentrations of GA4 and GA7. Injected PGRs, with the exception of BA injection, decreased concentrations of abscisic acid (ABA) and ABA glucose-ester at week 5 and/or week 7. Internal concentrations of trans-zeatin riboside (t-ZR) increased in response to all treatments at week 3 in genotype 276. In genotype 478, t-ZR only increased with treatments of BA or GA4/7 plus BA. Dihydrozeatin riboside concentrations increased in response to GA4/7 plus BA treatment at week 7 in genotype 276. Concentrations of isopentenyl adenosine declined with treatments of GA4/7 and GA4/7 plus BA in genotype 276 at week 5. In genotype 478, a similar decrease was caused by GA4/7 plus BA treatment. For both genotypes, the highest ratio of zeatin-type cytokinins to isopentenyl-type cytokinins occurred at weeks 5 and 7 after injection with GA4/7 plus BA. Stem-injection of GA4/7, especially in combination with BA, increased female cone yields significantly in genotype 276, but not in genotype 478.