The onset of reproduction is an important trait and is controlled by the FT1 locus in poplar (Populus sp.). Sequence variation in this locus is not well-understood. This study's aim is to identify sequence variation in the FT1 locus in a small population of Populus deltoides with varying reproductive onset. Gene specific primers were designed to amplify FT from 14 genotypes. The sequence analysis showed 12 single nucleotide polymorphisms and four insertion-deletion sites located in introns of FT1. No connection was observed between the identified polymorphisms and variation in reproductive onset. Further DNA sequencing of the genotypes needs to be done on the promoter region of FT1 to conduct an association study to statistically assess the connection between polymorphisms and phenotypic variation in a larger population. This information is expected to help us understand the genetic basis of phenotypic variation in reproductive onset.

Short rotation woody crops (SRWC) eastern cottonwood (Populus deltoides) and hybrid poplar plantations were established in 2021 in Pontotoc and Oktibbeha counties of Mississippi to study the biomass potential of SRWC for biofuel production. We used a novel backpack LiDAR system to measure forest metrics and harvested sample trees to build aboveground biomass (AGB) and leaf area index (LAI) equations. The results showed that LiDAR-derived variables accurately estimated aboveground biomass (R2 =0.81 and 29.22 % RMSE). However, the LAI estimation results showed that the LiDAR metrics moderately explained field measurements of LAI (R2 =0.31 and 18.05% RMSE) for individual-trees and poorly explained plot-level LAI measured with the LAI-2200C (R2 =0.11 and 66% RMSE). The backpack LiDAR system can be valuable for forest managers and researchers, enabling non-destructive AGB and LAI estimation. However, further research is required to overcome its limitations and achieve precise measurements of AGB and LAI.

The economic feasibility of producing biomass-based fuels requires high-yielding feedstocks to supply biomass to biorefineries. Populus trees are a potential biomass feedstock due to their high yield, but their high water requirement limits productivity under drought conditions. The number of genes controlling drought tolerance, and the long generation time for perennial species, slows cultivar development. Accelerated domestication proposes using the sequenced Populus genome to quickly incorporate target traits into productive clones by transgenesis. Six putative drought tolerance transcription factors: DREB2A, DREB2B, AtMYB, AREB1/ABF2, MYB, and NAC, had been previously identified and manipulated in eastern cottonwood (Populus deltoides). Three constructs of each gene were transformed into a P. deltoides background clone, including constitutive overexpression (OE), drought inducible OE, and knockdown. This greenhouse study examines the effect of these previously transformed constructs on drought tolerance by characterizing leaf abscission, leaf water potential, and growth under drought and well-watered conditions. AREB1/ABF2 constitutive OE lost significantly fewer leaves under drought than the Vector control, and had one of the lowest rates of leaf loss overall. Both DREB2A inducible OE and AREB1/ABF2 constitutive OE plants were more productive than the Vector control under drought conditions. MYB inducible OE was a productive construct and initially appeared to be drought tolerant. It is possible that this construct experienced xylem cavitation early on due to the severity of drought experienced by the large trees containing this construct. DREB2A inducible OE, AREB1/ABF2 constitutive OE, and MYB inducible OE were the most productive constructs as well as being likely to confer drought tolerance. Field trials would be the next step, providing a clearer picture of how these constructs would perform under natural conditions.

Polyclonal plantings of Populus deltoides are expected to display increased site resource use, productivity, and tolerance to stress through plasticity changes leading to niche differentiation (i.e changes to crown/canopy structures). In the present study, P. deltoides Clones S7C8, 110412, and polyclonal plots were tested for differentially expressed genes and enriched biological pathways between planting schemes. Transcriptomic analysis of leaves revealed upregulation of an active growth gene and gene family members that play important roles in plant stress and stress tolerance in polyclonal plantings. A gene associated with oxidative stress was upregulated in polyclonal plantings across all treatments. Secondary metabolic pathways including arginine and proline metabolism were upregulated in monoclonal plantings and downregulated in polyclonal plantings. Phenotypic results displayed greater aboveground biomass in polyclonal plantings. Results suggested a potential increased tolerance in polyclonal plantings to water and heat stress, including increased productivity and resource usage.