Improved experimental protocols to evaluate cold tolerance thresholds in Miscanthus and switchgrass rhizomes (original) (raw)
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Winter cold-tolerance thresholds in field-grown Miscanthus hybrid rhizomes
The cold tolerance of winter-dormant rhizomes was evaluated in diploid, allotriploid, and allotetraploid hybrids of Miscanthus sinensis and Miscanthus sacchariflorus grown in a field setting. Two artificial freezing protocols were tested: one lowered the temperature continuously by 1°C h–1 to the treatment temperature and another lowered the temperature in stages of 24 h each to the treatment temperature. Electrolyte leakage and rhizome sprouting assays after the cold treatment assessed plant and tissue viability. Results from the continuous-cooling trial showed that Miscanthus rhizomes from all genotypes tolerated temperatures as low as –6.5 °C; however, the slower, staged-cooling procedure enabled rhizomes from two diploid lines to survive temperatures as low as –14 °C. Allopolyploid genotypes showed no change in the lethal temperature threshold between the continuous and staged-cooling procedure, indicating that they have little ability to acclimate to subzero temperatures. The results demonstrated that rhizomes from diploid Miscanthus lines have superior cold tolerance that could be exploited to improve performance in more productive polyploid lines. With expected levels of soil insulation, low winter air temperatures should not harm rhizomes of tolerant diploid genotypes of Miscanthus in temperate to sub-boreal climates (up to 60°N); however, the observed winter cold in sub-boreal climates could harm rhizomes of existing polyploid varieties of Miscanthus and thus reduce stand performance.
Cold tolerance of forage plant species
Semina: Ciências Agrárias, 2018
The occurrence of frost in southern and southeastern Brazil affects pasture quality and limits the use of forage species with high yield potential. Therefore, elucidating the cold tolerance of individual forage species could facilitate the selection of species that will optimize production and animal feeding throughout the year. Accordingly, the aim of the present study was to evaluate the cold tolerance of forage species to low temperatures, based on cell membrane stability and photoinhibition. Alfalfa (Medicago sativa), sorghum (Sorghum bicolor), black oat (Avena strigosa), marandu grass (Urochloa brizantha), pearl millet (Pennisetum americanum), mombaça grass (Megathyrsus maximus), and bermuda grass ‘Tifton 85’ (Cynodon spp) plants were subjected to temperatures of 0.2, -0.9, -1.8, -2.7, -4.1, -4.6, and -6.2 °C for 1 h in a growth chamber. Cell membrane stability and photoinhibition were based on the electrical conductivity of leaf section solutions and chlorophyll fluorescence, ...
Miscanthus × giganteus grown in cool temperate regions of North America and Europe can exhibit severe mortality in the year after planting, and poor frost tolerance of leaves. Spartina pectinata (prairie cordgrass), a productive C4 perennial grass native to North America, has been suggested as an alternative biofuel feedstock for colder regions; however, its cold tolerance relative to M. × giganteus is uncertain. Here, we compare the cold tolerance thresholds for winter-dormant rhizomes and spring/summer leaves of M. × giganteus and three accessions of S. pectinata. All genotypes were planted at a field site in Ontario, Canada. In November and February, the temperatures corresponding to 50% rhizome mortality (LT50) were near −24°C for S. pectinata and −4°C for M. × giganteus. In late April, the LT50 of rhizomes rose to −10°C for S. pectinata but remained near −4°C for M. × giganteus. Twenty percent of the M. × giganteus rhizomes collected in late April were dead while S. pectinata rhizomes showed no signs of winter injury. Photosynthesis and electrolyte leakage measurements in spring and summer demonstrate that S. pectinata leaves have greater frost tolerance in the field. For example, S. pectinata leaves remained viable above −9°C while the mortality threshold was near −5°C for M. × giganteus. These results indicate M. × giganteus will be unsuitable for production in continental interiors of cool-temperate climate zones unless freezing and frost tolerance are improved. By contrast, S. pectinata has the freezing and frost tolerance required for a higher-latitude bioenergy crop.