Cultural treatments for accelerated growth and flowering of Panicum virgatum

Abstract

Background: Exploiting heterosis through hybrid breeding is essential to increase biomass yields of switchgrass (Panicum virgatum). However, life cycle timespan for clone evaluation for field evaluation is a major limitation to genetic selection. Methods & results: In an attempt to shorten the switchgrass life cycle timespan, we investigated the effect of four variables on the vegetative and reproductive morphology of the P. virgatum cultivar “Alamo”: day length, temperature, container size, and application of plant growth regulators. Seedlings grew fastest and reached flowering fastest under 18 hours of daylight with growth being severely and mildly inhibited at 8 h and 23 h, respectively. Under the optimum (18 h) photoperiod, day temperature of 25°C led to the fastest growth and flowering whereas a 5°C increase or decrease inhibited growth and flowering. Within the 18 h/25°C treatment, 44% of plants flowered after 90 d and >15% of plants reached full anthesis or post-anthesis seed set. Conclusions: Allowing 45 d for seed set and 30 d for cold stratification, generation time for the post-anthesis plants grown in 18 h/25°C conditions is approximately 165 days, allowing for the production of two generations of switchgrass per year for accelerating germplasm development for this perennial bioenergy crop.

Acknowledgements

CNS, SJ, JB, and LA designed the experiments; LA implemented the experiments, analyzed the data, and prepared the manuscript; EH collected the data and maintained the plants. All authors read and approved the final manuscript. M. Alexander, E. Kraft, and M. Hanson assisted with plant maintenance and data collection. This work was supported by Genera Energy, Inc. and Agriculture and Food Research Initiative Competitive Grant no. 2011-68005-30410 from the USDA National Institute of Food and Agriculture. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the USDA, University of Tennessee, or Genera Energy.

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Executive summary

•	“Alamo” switchgrass grown from seed in controlled environment chambers showed the most rapid growth and flowering under 18 hours of daylight with growth being severely and mildly inhibited at 8 h and 23 h, respectively.
•	Under the optimum (18 h) photoperiod, a day time temperature of 25°C led to the fastest growth and flowering while a 5°C increase or decrease inhibited growth and flowering.
•	Within the 18 h/25°C treatment, 44% of plants flowered after 90 d and 11 plants were in reproductive stage R4 (full anthesis) or R5 (post-anthesis seed set).
•	Application of these treatments may decrease generation time of switchgrass by up to 20% and allow for the production of two generations of switchgrass per year.