Diallel Analysis of Biomass and Ethanol Yield in Leaves versus Stems of Lowland Switchgrass

Switchgrass (Panicum virgatum L.) is a warm season perennial grass used widely as a forage crop. This research seeks to address improving biomass yield and predicted ethanol yield through certain traits by the following objectives: (1) differences in average biomass and predicted ethanol yields from leaves versus stems, (2) genetic variance and heritability estimates of biomass and ethanol yield traits (3) general (GCA) and specific combining ability (SCA) among the five parents for biomass and ethanol yield, and (4) correlations between agronomic and morphological traits. Five parents with varying morphological traits were crossed in a diallel design, excluding selfs. Clonal replicates of all crosses were planted at ETREC in Knoxville, TN and PREC in Crossville, TN.

The mean leaf biomass yield in 2012 was 22.9 g plant^-1 [ grams per plant] and 15.2 g plant-1 at two locations. In 2013 mean values were 41.5 g plant-1 and 57.9 g plant^-1. The mean stem biomass values were 29.4 g plant^-1 and 15.6 g plant^-1 in 2012. In 2013 the mean stem biomass yield increased to 84.6 g plant^-1 and 98.6 g plant^-1. The average leaf to plant ratio in 2012 was 0.55 and 0.37 in 2013. The mean for predicted leaf ethanol in 2012 was 65.8 mg g^-1 DM [milligrams per gram dry matter] and was 68.4 mg g^-1 DM in 2013. Predicted stem ethanol mean was 61.67 mg g^-1 DM.

GCA for leaf biomass ranged from -2.90 to 1.8 g plant^-1, and SCA values ranged from -5.7 to 7.1. GCA values -7.8 to 9.2 g plant-1 for stem biomass yield, and SCA values ranged from -10.9 to 11.0 g plant-1. Predicted leaf ethanol yield GCA values ranged from -0.77 to 0.87, and SCA values ranged from -1.3 to 0.84. GCA values for predicted stem ethanol ranged from -3.2 to 2.6 mg g^-1 DM, and SCA values from -1.2 to 1.3 mg g^-1 DM. Narrow sense heritability estimates ranged from 0.03 to 0.23. Broad sense heritability estimates ranged from 0.16 to 0.6. High parent heterosis was observed in all traits. There were correlations between agronomic traits and morphological traits.