Quantitative Trait Loci (QTL) for Forage Traits in Intermediate Wheatgrass When Grown as Spaced-Plants versus Monoculture and Polyculture Swards

Abstract

It has been hypothesized that the genetic control of forage traits, especially biomass, for grass plants growing as spaced-plants versus swards is different. Likewise, the genetic control of compatibility in grass–legume polyculture mixtures is assumed to be different than for forage production in a grass monoculture. However, these hypotheses are largely unvalidated, especially at the DNA level. This study used an intermediate wheatgrass mapping population to examine the effect of three competition environments (spaced-plants, polyculture, and monoculture) on classical quantitative genetic parameters and quantitative trait loci (QTL) identification for biomass, morphology, and forage nutritive value. Moderate to high heritable variation was observed for biomass, morphological traits, and nutritive value within all three environments (H ranged from 0.50 to 0.87). Genetic correlations (rG) among environments for morphology and nutritive value were predominantly high, however, were moderately-low (0.30 to 0.48) for biomass. Six biomass QTL were identified, including three on linkage groups (LG) 1, 6, and 15 that were only expressed in the monoculture environment. Moreover, three biomass QTL on LG 10, 14, and 15 exhibited significant QTL by environment interactions. This study verified that the genetic control of grass biomass in a monoculture versus a grass–legume mixture is only partially the same, with additional genes expressed in monoculture, and that biomass in widely spaced-plants versus swards is predominantly under different genetic control. These results indicate that selection for improved grass biomass will be most successful when conducted within the targeted monoculture or polyculture sward environment per se.

Floret site utilization and reproductive tiller number are primary components of grain yield in intermediate wheatgrass spaced plants

“…Lazenby and Rogers, 1964;Asay and Johnson 1997;Waldron et al, 2008). This was validated in a recent QTL mapping study of IWG forage traits, where in some cases varying QTL positions and allele effects and were detected for forage biomass and fertile tiller number plant -1 in spaced plant and sward environments (Mortenson et al, 2019). However, whether this persists in more recently developed germplasm for grain and other yield component traits has not yet been published.…”

“…This suggests that there is limited evidence for a tradeoff between excessive reproductive tillering and yield per spike in spaced plants and again highlights the importance of determining whether excessive tillering is advantageous for yield in a sward environment and if the tendency of a genotype to tiller is stable across these two growing environments. Results from Mortenson et al (2019) suggest relatively low phenotypic and genetic correlations (r p = .10 and r g = .47) between fertile tiller number per plant in IWG spaced plants compared with monoculture sward environments.…”

“…This increase was also accompanied by near doubling of reproductive tiller number, and a decrease in almost all other yield component and biomass traits (yield per spike, TGW, spikelets per spike, florets per spikelet, flag leaf area, and stem diameter). Larson et al (2019) also reported the performance of IWG in spaced plants over 2 and 3 yr in two locations. Although they did not report yield per plant, similar decreases over time in yield per spike, seed mass, seed dimensions, florets per spikelet, and stem width were observed, though whether this decrease occurred between the second or third year was variable depending on the trait.…”

“…Crop Science each including a lemma, palea, and a caryopsis with varying levels of fertility (Larson et al, 2019). In 1983, researchers at the Rodale Research Center (Kutztown, PA) began surveying a panel of nearly 100 perennial grass species for their domestication potential, and in 1988 initiated germplasm evaluation of IWG (Wagoner, 1990).…”

Nested association mapping reveals the genetic architecture of spike emergence and anthesis timing in intermediate wheatgrass

“…This finding is supported by the vast differences in GDD accumulation across the two sites (Supplementary Figure S1). Furthermore, previous work in IWG has also shown that the presence and location of QTL can vary depending on whether phenotypic data are tested on an individual environment basis or averaged across environments ( Larson et al 2019 ; Mortenson et al 2019 ).…”