Abstract
Hybrid vigor and polyploidy are genetic events widely utilized to increase the productivity of crops. Given that bioenergy usage needs to be expanded, we investigated triploid hybrid vigor in terms of the biology of biomass-related willow traits and their relevance to the control of biomethane production. To produce triploid hybrid genotypes, we crossed two female diploid Swedish cultivars (Inger, Tordis) with two male autotetraploid willow (Salix viminalis) variants (PP-E7, PP-E15). Field studies at two locations and in two successive years recorded considerable midparent heterosis (MPH%) in early shoot length that ranged between 11.14 and 68.85% and in the growth rate between 34.12 and 97.18%. The three triploid hybrids (THs) developed larger leaves than their parental cultivars, and the MPH% for their CO2 assimilation rate varied between 0.84 and 25.30%. The impact of hybrid vigor on the concentrations of plant hormones in these TH genotypes reflected essentially different hormonal statuses that depended preferentially on maternal parents. Hybrid vigor was evinced by an elevated concentration of jasmonic acid in shoot meristems of all the three THs (MPH:29.73; 67.08; 91.91%). Heterosis in auxin-type hormones, such as indole-3-acetic acid (MPH:207.49%), phenylacetic acid (MPH:223.51%), and salicylic acid (MPH:27.72%) and benzoic acid (MPH:85.75%), was detectable in the shoots of TH21/2 plants. These hormones also accumulated in their maternal Inger plants. Heterosis in cytokinin-type hormones characterized the shoots of TH3/12 and TH17/17 genotypes having Tordis as their maternal parent. Unexpectedly, we detected abscisic acid as a positive factor in the growth of TH17/17 plants with negative MPH percentages in stomatal conductance and a lower CO2 assimilation rate. During anaerobic digestion, wood raw materials from the triploid willow hybrids that provided positive MPH% in biomethane yield (6.38 and 27.87%) showed negative MPH in their acid detergent lignin contents (from –8.01 to –14.36%). Altogether, these insights into controlling factors of above-ground growth parameters of willow genotypes support the utilization of triploid hybrid vigor in willow breeding to expand the cultivation of short rotation energy trees for renewable energy production.
Highlights
IntroductionPlants, as sessile organisms, are the primary victims of extreme and damaging environmental conditions
Climate change interacts with the plant kingdom in a complex way
Traditional forestry, short rotation forestry (SRF) that entails a high density of plants and frequent harvesting can offer an alternative silvicultural system to be harnessed for climate change mitigation and phytoremediation goals
Summary
Plants, as sessile organisms, are the primary victims of extreme and damaging environmental conditions. They play a positive role in climate change mitigation and renewable energy production. Different forest ecosystems and management practices should be evaluated for their forestation potential to insure high C sequestration capacity into both biomass and soil stocks. In this respect, shrub willows grown as woody crops have outstanding potential to serve as an optimal feedstock to produce bioenergy, biofuels, and bioproducts with environmental and rural development benefits (Clifton-Brown et al, 2019). Traditional forestry, short rotation forestry (SRF) that entails a high density of plants and frequent harvesting can offer an alternative silvicultural system to be harnessed for climate change mitigation and phytoremediation goals (refer to the review by Capuana, 2020)
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