2015 RESEARCHS witchgrass (Panicum virgatum L.) is a predominant component of the North American prairie. It is adapted to a wide range of landscapes and ecosystems in North America (Casler et al., 2007a). Its traditional uses include pasture or hay production, prairie renovation, and erosion control (Vogel, 2004). After the 1991 decision by the USDOE to develop switchgrass as a dedicated lignocellulosic feedstock for bioenergy production, there has been overwhelming motivation for research on this species to understand its agronomy and biology, as well as to develop genomics tools to improve its biomass yield potential and conversion efficiency. The species needs significant improvement in biomass yield potential for its competitive use as a bioenergy feedstock. Cultivar breeding to improve biomass yield, targeting bioenergy feedstock use, is underway at several universities and USDA Agriculture Research Centers.Conventional breeding to improve yield relies on capturing both additive and dominant genetic variation. Additive genetic variance, as well as part of the dominant genetic variance, can be captured through recurrent selection using phenotypic or genotypic selection on the basis of half-sib, full-sib, or other types of progeny performance. The dominant genetic variation is responsible for hybrid vigor or heterosis, which can be better exploited through hybrid cultivar development. Heterosis in plant vigor, ABSTRACT Biomass yield improvement of switchgrass (Panicum virgatum L.) is critical for its use as a viable bioenergy feedstock. Population improvement through accumulation of favorable genes and exploitation of heterosis are two ways to improve biomass yield. The objective of this study was to assess biomass yield heterosis in biparental crosses between genotypes of lowland switchgrass. Forty-four genotypic crosses between two predominant lowland populations 'Alamo' and 'Kanlow', along with nine crosses among genotypes of other lowland germplasm, were evaluated in Knoxville and Crossville, TN. The experiment was established in summer 2014 using a randomized complete block design with three replications. Each plot within each replicate was a single row of 10 plants planted on 30-cm spacing, and rows were spaced 90 cm apart. Parental clones of 22 crosses were evaluated only in Crossville sites. Biomass yield was recorded at the end of fall 2015 and 2016. Biparental crosses were different in biomass yield (p < 0.001), and significant genotype ´ environment interaction for biomass yield was observed. Nineteen crosses produced 18 to 53% higher biomass compared with the average of the Alamo and Kanlow population bulks. Average yields of a matured stand ranged from 11.16 to 23.3 t ha −1 . Four crosses demonstrated 25 to 41% midparent heterosis (MPH), and one cross showed 23% high-parent heterosis. Two of the crosses showed negative MPH. Heterosis in both directions suggests presence of both favorable and unfavorable complementary dominant genes in switchgrass. These findings could help improve cultivar breedi...

Switchgrass (Panicum virgatum L.), a native of the North American prairies, has been selected for bioenergy research. With a focus on biomass yield improvement, this study aim (i) to estimate the genetic variation in biomass yield and important agronomic traits in ‘Alamo’, (ii) to determine correlations between biomass yield and agronomic traits, and (iii) to compare efficiency of phenotypic selection from a sward plot and advanced cycle half‐sibs (ACHS) on the basis of space‐plant performance. Sixty‐two Alamo half‐sib families (AHS) from a 4‐yr‐old Alamo sward and 20 advanced cycle half‐sib families (ACHS) were evaluated in replicated field trials under simulated swards in Knoxville and Crossville, TN. Results showed significant variation (P < 0.05) among AHS for biomass yield, tillering ability, and spring vigor, suggesting the importance of additive genetic variation in these traits. Overall mean biomass yield of AHS was not different from the Alamo control, demonstrating the inefficiency of phenotypic selection from swards. Mean biomass yield of ACHS was 15 and 20% less than that of the control and AHS, respectively. Such results could be attributable to the influence of environment and genotype × environment interaction. However, results showed great potential for biomass yield improvement through selection on the basis of family performance. Using 10% selection intensity, parental control of two, and a narrow‐sense heritability estimate of 0.11, gain per cycle selection from half‐sib family selection is estimated to be 23%. Spring vigor showed potential use for indirect selection due to its high genetic correlation (rG = 0.75) with biomass yield. However, it is impeded by the low heritability estimate (h2 = 0.34).

Switchgrass (Panicum virgatum L.) is a warm-season, perennial grass valued as a promising candidate species for bioenergy feedstock production. Biomass yield is the most important trait for any bioenergy feedstock. This study was focused on understanding the genetics underlying biomass yield and feedstock quality traits in a “Kanlow” population. The objectives of this study were to (i) assess genetic variation (ii) estimate the narrow sense heritability, and (iii) predict genetic gain per cycle of selection for biomass yield and the components of lignocelluloses. Fifty-four Kanlow half-sib (KHS) families along with Kanlow check were planted in a randomized complete block design with three replications at two locations in Tennessee: Knoxville and Crossville. The data were recorded for two consecutive years: 2013 and 2014. The result showed a significant genetic variation for biomass yield (p < 0.05), hemicellulose concentration (p < 0.05), and lignin concentration (p < 0.01). The narrow sense heritability estimates for biomass yield was very low (0.10), indicating a possible challenge to improve this trait. A genetic gain of 16.5% is predicted for biomass yield in each cycle of selection by recombining parental clones of 10% of superior progenies.

Heterosis plays an important role in switchgrass (Panicum virgatum L.) breeding. To identify superior clones for hybrid development through seasonal single cut, 10 crosses derived from ‘Alamo’ × ‘Kanlow’ and parents were evaluated. The experiment was planted in 2018 using a randomized complete block design with two replications at two locations in Tennessee: the East Tennessee Research and Education Center (ETREC), Knoxville, and the Plateau Research and Education Center (PREC), Crossville. The crosses and their parents were evaluated for biomass yield, plant height, and clonal mass in the fall of 2019 and 2020. The crosses were significantly different in biomass yield within and across locations (P ≤ .05). Average biomass yield of the crosses ranged from 7.1 to 8.7 Mg ha−1 at ETREC and from 10.0 to 11.8 Mg ha−1 at PREC. The crosses demonstrated an average of 46% mid‐parent heterosis (MPH) and 24% high‐parent heterosis (HPH) for biomass yield across the two locations. The MPH and HPH were 3 and −1.3% for plant height and 12 and 1% for clonal mass, respectively. Moderate to strong positive association was found between clonal mass scores and biomass yield at individual locations across years and across locations and years (r = 0.37–0.79, P ≤ .05). The association between biomass yield and plant height was inconsistent (r = −0.24 to 0.67, P ≤ .05). The findings of biomass yield heterosis in these crosses suggested the potential of hybrid cultivars for biomass yield improvement in lowland switchgrass.