Exploiting Plant Growth Promoting Rhizobacteria for the Conservation and Regeneration of the Near Threatened Chilgoza Pine (Pinus gerardiana) In Dir Upper, Khyber Pakhtunkhwa, Pakistan

Chilgoza pine (Pinus gerardiana) forests in Upper Dir are facing serious threats due to poor natural regeneration and slow growth. This study was conducted to isolate and identify plant growth-promoting rhizobacteria (PGPR) from the rhizospheric soils and root saplings of Chilgoza pine, evaluate their effects on seed germination and seedling growth, and compare their performance with phytohormones. The study area was Narkoon, located in the Pathrak forest range of Upper Dir district. The isolated bacterial strains were Enterobacter (from soil) and Klebsiella spp. (from roots). Chilgoza pine seeds were treated with gibberellic acid (150 ppm), PGPR, and their combinations. The experiment was carried out under controlled conditions in a growth chamber (CRD) and in a forest nursery (RCBD). Germination was recorded when the radicle reached 2 mm in length, and growth parameters were measured after one growing season. One-way ANOVA was applied to assess significant differences among treatments. The results showed that seeds treated with Klebsiella pneumoniae + 150 ppm gibberellic acid exhibited the highest germination energy (83%). Both Enterobacter cancerogenus and Klebsiella pneumoniae, alone or in combination with gibberellic acid, significantly enhanced germination percentage, mean daily germination, germination index, and seedling growth traits. Notably, (E. cancerogenus + 150 ppm gibberellic acid) resulted in the greatest root length (7.8 cm) and shoot length (14.6 cm). Statistical analysis confirmed significant treatment effects on germination and growth parameters (p < 0.05). Overall, the study demonstrates that PGPR inoculation combined with gibberellic acid can substantially improve seed germination and seedling growth in P. gerardiana.