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.
Highlights
Most forage breeding programs have utilized spaced-plant evaluation to select breeding materials.the ability of spaced-plants to predict sward biomass has been questioned [1]
The M26 × M35 intermediate wheatgrass mapping population was evaluated over two years in three competition environments to determine the effect of these environments on classical quantitative genetic parameters and on quantitative trait loci (QTL) identification for biomass, morphology, and forage nutritive value
Moderate to high heritable variation was observed for intermediate wheatgrass biomass and morphological traits within the three environments (H ranged from 0.50 to 0.87), and with few exceptions, the forage nutritive value traits were highly heritable (H > 0.70) within all three environments
Summary
Most forage breeding programs have utilized spaced-plant evaluation to select breeding materials.the ability of spaced-plants to predict sward biomass has been questioned [1]. Agronomy 2019, 9, 580 to intra-specific competition, and, not having been exposed to inter-specific competition, will not possess the optimal biological characteristics conducive to coexistence and compatibility in grass–legume polyculture mixtures [3]. Breeding for improved ECA is predicted to reduce competitive exclusion between plant species, whereas reciprocal recurrent breeding for ECA between grasses and legumes is predicted to improve performance of grass–legume mixtures [2,3,4]. This hypothesis is largely unvalidated with only limited genetic studies attempting to investigate the role of genetics in grass–legume mixtures [4,5]
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