Quantitative Trait Loci (QTL) for forage traits in intermediate wheatgrass when grown as spaced-plants versus monoculture and polyculture swards

Authors: MORTENSON, JOHN - Utah State University; Waldron, Blair; Larson, Steven; Jensen, Kevin; DEHAAN, LEE - The Land Institute; Peel, Michael; JOHNSON, PAUL - Utah State University; CREECH, J - Utah State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2019
Publication Date: 9/25/2019
Citation: Mortenson, J.S., Waldron, B.L., Larson, S.R., Jensen, K.B., DeHaan, L.R., Peel, M., Johnson, P.G., Creech, J.E. 2019. Quantitative Trait Loci (QTL) for forage traits in intermediate wheatgrass when grown as spaced-plants versus monoculture and polyculture swards. Agronomy Journal. 9(10). https://doi.org/10.3390/agronomy9100580.
DOI: https://doi.org/10.3390/agronomy9100580

Interpretive Summary: Increases in forage productivity of cool-season grasses due to breeding is often less than anticipated. This lack of response may be because plant breeders often conduct evaluations as widely-spaced individual plants which is not like the production environments of monoculture and mixture swards. Many assume that the genetic control of forage traits, especially biomass, for grass plants growing as spaced-plants versus swards and monocultures versus mixtures is at least partially different, however, these assumptions are largely untested, especially at the DNA level. Therefore, this study used an intermediate wheatgrass genetic population to examine the genetic control of forage traits when grown under three different competition environments (spaced-plants, and grass monoculture and grass-legume mixture swards). Biomass, morphological traits, and forage nutritive value were all moderatly to highly heritable within all three environments and genetic control of forage nutritive value was similar among all environments. However, this study verified that the genetic control of grass biomass in a nonculture 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 grass monoculture or grass-legume mixture sward environment per se.

Technical 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 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 .87). Genetic correlations (rc) 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 an allelic by environment interaction. 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.