Phenotypic Selection Improves Biomass Yields of an Alamo Population of Switchgrass.

Switchgrass (Panicum virgatum L.) cultivar breeding at the University of Tennessee, Knoxville is focused on biomass yield improvement for use as a bioenergy feedstock. Using four-year-old sward plots of ‘Alamo’ population established at the Holston unit of  East Tennessee Research and Education Center, over 230 individual plants were selected based on phenotypic evaluation in the fall of 2011. Open pollinated seeds were harvested separately from each selected plant that constituted a halfsib family.  Based on seed yield and germination, 62 halfsib families were retained for evaluation at two Tennessee locations, Knoxville and Crossville. The halfsib family evaluation trial was established in spring 2012 as a spaced-planted nursery, using a randomized complete block design with 3 replications. Each family in each replication was planted in a single-row-plot of 9 plants 30cm  apart, and 90cm between rows. The biomass yield was recorded from established plots in the fall of 2013. Results demonstrated significant genetic variation among halfsib families. Compared to the original population, the mean biomass yield of the halfsib families at Knoxville site was 14% higher indicating potential yield gain that could be made using phenotypic selection. However, at the Crossville location, the mean performance of the selected families was 10% below the original population, indicating the potential hurdle attributable to the genotype by environment interaction. A few of the halfsib families have shown superior performance at both locations.  This indicates that phenotypic selections could be made for development of varieties with stable performance in a broader range of environment.