Increased adaptation of an energy willow cultivar to soil salinity by duplication of its genome size

Soil salinity can limit the use of marginal lands for biomass production based on cultivation of short-rotation woody crops as energy willow. Here, we compare salt stress responses of the diploid, productive cultivar (Energo), and its artificially produced autotetraploid (PPE-2; PPE-7; PPE-13) variants. After pre-testing the effects of various salt concentrations, willow plants with different genome sizes were exposed to 1.5 g NaCl kg(-1) soil (electrical conductivity (EC) value: 7.04 mS/cm). Digital imaging of shoot surface area (green pixel) and root surface (white pixel) indicated variable improvements in growth responses of tetraploids relative to diploid ones in saline soils. After nine weeks of salt stress, increase in salt adaptation capability of tetraploid plants was indicated by larger biomass, leaf and root weights under salinity (1.5 g NaCl kg(-1) soil) relative to diploids. Biomass weights were significantly higher in the case of tetraploid PPE-2 plants with increased water consumption and leaf water content than of diploid plants. The inhibitory effect of salt stress on photosynthetic assimilation rates was less significant in plants with doubled genome. The Na+ accumulation was reduced in leaves of tetraploids and increased in their roots, while the K+ ion content was higher in their leaves than in diploids. Tetraploidy improved K+/Na+ ratio in leaves and roots of willow plants under normal soil condition. This parameter was less reduced in tetraploid leaves exposed to salt stress. The described tetraploid energy willow genotypes with salt tolerance can play a role in the extended use of green energy.