Genetic correlations between switchgrass performance in sward conditions and surrogate measures

Authors: TILHOU, NEAL - Former ARS Employee; CASLER, MICHAEL - Retired ARS Employee

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2022
Publication Date: 5/5/2022
Citation: Tilhou, N., Casler, M. 2022. Genetic correlations between switchgrass performance in sward conditions and surrogate measures. Crop Science. 62(4):1511-1521. https://doi.org/10.1002/csc2.20767.
DOI: https://doi.org/10.1002/csc2.20767

Interpretive Summary: Perennial energy grasses, such as switchgrass, represent a potentially important component of sustainable bioenergy production. Breeding new switchgrass varieties is an essential element for development of these sustainable production practices. There are a number of essential and critical decisions about breeding methods that must be made by all switchgrass breeders. One of these decisions is exactly how to evaluate improved switchgrass seed samples to determine which ones should be advanced in the breeding program. This study evaluated five different plot methods, consisting of plant spacings ranging from one plant per 10 square feet to one plant per square inch. The study showed that all five spacings had very high correspondence with each other, essentially all capable of identifying the seed lots with the highest biomass production potential. Unexpectedly, the study showed that the spacing of one plant per square foot had consistently the highest biomass yield, by 50% over the next best spacing. These results have generated an important question about plant spacings in commercial biomass production fields that will be an important consideration for agronomy and genetics researchers.

Technical Abstract: Switchgrass breeding experiments use spaced seedling plots for evaluations of biomass yield, but prior studies are ambiguous about the relationship between performance in spaced plots and commercial seeded sward performance. This study evaluated 52 half-sib switchgrass families across two years to determine the correlations between of four different plot types (including seeded swards) and four individual plant measures. Overall biomass yield reliability was 0.53 with a mean of 0.47 for individual plot types. Plots (1.62 m2) which contained with 3, 6, and 18 plants had mean yields of 5.92, 8.04, and 11.06 Mg ha-1, respectively, while seeded sward plots had a mean of 5.37 Mg ha-1. In a mixed-model analysis, the largest proportion of family variance was accounted for by the main effect (48%), while the plot type-by-family effect was only 17% of family variance. These results indicate that spaced plant plots are reasonable surrogates for biomass performance in sward conditions. Individual plant surrogates for sward yield varied due to the genetic background of the families in the study. Yield of families derived from the Liberty cultivar (n=32) were significantly correlated with winter survivorship scores (0.46). A diverse set of families from the lowland ecotype (n=20) had significant yield correlations with plant height (0.72) and heading date (0.50). This study unexpectedly emphasized a major difference in performance among the plot types, specifically that seeded swards have depressed yield due to high plant density. This should encourage further research for the mechanism behind this difference in performance.