Phenotyping Winter Dormancy in Switchgrass to Extend the Growing Season and Improve Biomass Yield

Seasonal changes have a great impact on plant development and crop production. For warm season grasses like switchgrass (Panicum virgatum), the transition from a long-day, hot summer to a short-day cold winter will induce a phenomenon called winter dormancy. Like most perennial warm season species, switchgrass undergoes growth suspension in winter as a surviving strategy in temperate climates to protect their meristems from cold injuries and dehydration, while storage organs below ground drive spring regrowth when conditions become favourable.

In this paper, the authors described a reliable phenotyping method for winter dormancy in switchgrass using various traits including regrowth height after clipping in early fall (FRH), senescence percentage, date of spring regrowth (SRD), and flowering date (FD). A diverse panel of switchgrass germplasm was used to evaluate the phenotyping approaches. The panel consisted of 36 accessions that included 14 uplands, 17 lowlands, and 5 intermediate ecotypes, in addition to the parents of the mapping populations AP13 × VS16. Dormancy phenotypic data evaluated consisted of 1) Level of senescence (senescence %) and plant regrowth height after clipping in the fall (FRH), 2) Date of spring regrowth initiation (SRD), 3) Date of flowering (FD), and 4) Dry biomass weight.

Fall regrowth height data showed a normal distribution with a slight left skewness, signifying a high proportion of lower FRH values in the population. Senescence % distribution was also normal but skewed to the right, indicating a high proportion of higher senescence values in the population. This is expected because most of the upland and intermediate genotypes enter dormancy and senesce much earlier than lowland accessions. The data distribution for SRD was normal but with some outliers in both tails. For FD, the distribution was less bell-shaped and left skewed, suggesting a wide window of flowering and a large variation of flowering dates in the population.

In conclusion, combining the variables FRH, senescence, and SRD in a selection index may provide a reliable tool to phenotype winter dormancy in switchgrass. The strong correlation of these variables with biomass yield makes them useful candidates for the manipulation of the duration of dormancy to increase the growing season and consequently improving biomass production.

Article by Rasyidah Mohamad Razar and Ali Missaoui, from University of Georgia, Athens, GA, USA.

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