# Seed Zone Nutritional Sensitivity and Hormone-Independent Rooting in Sugar Pine (Pinus lambertiana Dougl.): A Two-Phase Evaluation of Nutrient Solutions and Rooting Environments

## TL;DR

This study explores how different seed zones of sugar pine respond to nutrients and rooting environments, finding that northern seed sources are more sensitive to high nutrients and hormone-free rooting works best.

## Contribution

The study identifies seed zone-specific nutritional sensitivities and demonstrates hormone-independent rooting success in sugar pine propagation.

## Key findings

- Northern seed zones showed significant survival decline under high-nutrient solutions, while southern zones maintained high survival and increased branching.
- Rooting success occurred only in non-mist environments and was highest in untreated cuttings.
- Hormone treatments did not improve rooting success compared to untreated controls.

## Abstract

Clonal propagation of rust-resistant sugar pine (Pinus lambertiana Dougl.) is currently limited by extreme rooting recalcitrance and highly variable donor responses to nursery management. This study identified seed zone-specific nutritional sensitivities and evaluated rooting success; we hypothesized that northern seed sources would exhibit greater sensitivity to high nutrient loads and that stable microclimates would outperform high-intensity rooting systems. In Study 1, seedlings from five United States Department of Agriculture seed zones were grown for 27 weeks in five nutrient solutions (tap-water control, modified Hoagland, Foliage-Pro®, Andrejow, and FloraNova®) spanning 0.72–3.00 dS m−1. The nutrient-rich Foliage-Pro® and FloraNova® solutions defined the upper end of the nutrient-intensity range and revealed strong seed zone contrasts: northern zones (526, 550) showed marked sensitivity, with survival declining from 70 to 100% in the control to 15–40% under the highest-EC formulations, whereas southern zones (992, 993) maintained high survival (≥75%) across all treatments and exhibited increased branching (up to 3.7 branches plant−1) under higher-nutrient solutions. In Study 2, stem cuttings were rooted in three environments (non-mist, hydroponic, and aeroponic) and four hormone treatments (control, Clonex®, Dip’n Grow®, and IBA + Ethrel). Rooting occurred exclusively in the non-mist propagator; untreated controls achieved 65% success and outperformed all hormone treatments (0–10%). These results demonstrate that P. lambertiana propagation depends on seed zone-specific donor nutrition and stable, hormone-independent rooting environments.