This study was conducted to evaluate drought tolerance and persistence in a germplasm of smooth bromegrass and association of forage productivity with different traits. Thirty‐six genotypes of smooth bromegrass were clonally propagated and evaluated under two soil moisture environments for three years (2013–2015). High genotypic variation was observed among genotypes for all the measured traits. Drought stress decreased mean values for traits related to productivity. Also, the long‐term stress for three years reduced the persistence of plants. Results indicated that indirect selection based on components of forage yield, which had high heritability and high correlation with yield, would be more effective to improve drought tolerance in this germplasm. The results of principal component analysis showed that there was a negative relationship between phenological traits with the persistence‐related traits and yield production. This suggests that selection for earliness may indirectly promote persistent genotypes. The results showed that some Hungarian genotypes are valuable gene sources for persistence. The most persistent genotypes from both groups (Iranian and foreign) were identified using the biplot method. These genotypes may be useful for the development of populations for future studies.

The genetic basis of physiological responses to drought and its association with productivity, persistence and summer dormancy is not clear in orchardgrass (Dactylis glomerata L.). Thirty-six orchardgrass genotypes were evaluated under water stress and non-stressed conditions during 2 years (2013–14). High genotypic variation was observed for all of the agronomic and physiological traits. Water stress reduced dry matter yield, relative water content and chlorophyll content while significantly increasing carotenoids, water-soluble carbohydrates, proline and chlorophyll a : b ratio. The results indicated that carotenoids and proline accumulation could not be used for discriminating drought-tolerant genotypes of orchardgrass, whereas water-soluble carbohydrates may be used to achieve this purpose. Moreover, the results showed that the stable genotypes that have lower changes in productivity from normal to water-stress environments also have more persistence. No association was found between summer dormancy and drought tolerance measured by both physiological and yield-based drought-tolerance indices. Some of the drought-tolerant genotypes had relatively high persistence and better autumn recovery, a characteristic useful for the development of new synthetic varieties.

No abstract

Polycross designs bridge the two usual mapping approaches (bi-parental mapping and association analysis) and increase mapping power by incorporating greater genetic diversity. In this study, we used diverse genotypes selected from polycrossed progenies to identify marker loci associated with a set of seed- and forage-related traits as well as drought tolerance in orchardgrass (Dactylis glomerata L.). Associations were estimated between phenotypic traits and 923 DNA markers (including 446 inter-simple sequence repeats and 477 sequence-related amplified polymorphism markers). Positive relationship was found between forage yield and seed yield under normal and water-stress conditions, indicating that simultaneous improvement of seed and forage yield could be achieved in orchardgrass. The results of population structure analysis identified five main subpopulations possessing significant genetic differences. Under normal and water-stress conditions, respectively, 341 and 359 markers were significantly associated with the studied traits. Most of these markers were associated with more than one trait. Water-environment specificity of trait-associated markers indicates that genotype × environment interactions influence association analysis. However, 75 stable associations were identified across two moisture conditions for traits such as seed and forage yield. Marker–trait association revealed that markers M1/E1-5, M2/E6-5, M3/E4-6, P14-7 and P845-7 were consistently linked with drought-tolerance index. The identified marker alleles associated with multiple traits across environments may be considered for further analysis for their chromosome locations, the corresponding sequences and their potential functions.

In smooth bromegrass (Bromus inermis Leyss), few efforts have been made to develop rapid and reliable physiological indices for selection of persistent and drought‐tolerant genotypes. In addition, the association of these indices with seasonal growth activity, such as summer dormancy and autumn recovery, has not been studied. In this research, 36 genotypes of smooth bromegrass were clonally propagated and evaluated under water stress and nonstress conditions during 2013 to 2014. Water stress greatly influenced physiological functions and persistence, which affect plant growth and biomass production. Among the 36 randomly selected genotypes from the progeny of 25 half‐sib polycross families of smooth bromegrass, high genotypic variation was observed for all measured traits. Leaf proline content was not correlated with drought tolerance and persistence. However, carotenoid content and water‐soluble carbohydrates were correlated with drought tolerance and can be suggested for indirect selection of drought‐tolerant genotypes. Three genotypes (G8IHA, G13HUN, and 32HUN) were found to be more drought tolerant than others based on stress tolerance index, higher dry matter yield, summer dormancy, and relatively higher persistence and autumn recovery.

Genetic analysis of seed production and the effect of water stress on seed and forage production have not been addressed simultaneously in orchardgrass (Dactylis glomerata L.). Thirty-six genotypes of orchardgrass were clonally propagated and evaluated in the field under two moisture environments (normal and water stress) during 3 years (2013–15). A high degree of variation was observed among genotypes for all of the measured traits. Water stress had a negative effect on seed weight per plant and dry matter biomass per plant, and it reduced genotypic variation for most of the traits. A significant and positive correlation was found between seed weight per plant and dry matter biomass per plant, which suggested that simultaneous selection for both traits is possible in normal as well as water-stress environments. The results also indicated that traits explaining seed and forage production variability were not exactly the same in water-stress and non-stress environments. Therefore, indirect selection based on seed weight and dry matter biomass components under normal and water-stress conditions may result in genotypes with different performances. In both normal and water-stress environments, some genotypes were identified as superior with respect to high seed weight and dry matter biomass per plant. These genotypes can be used for further studies to improve seed weight and dry matter biomass per plant, simultaneously.

The genetic basis of post-drought recovery, summer dormancy and persistence under drought stress is little investigated in orchardgrass (Dactylis glomerata L.). In this study, polycross populations (half-sib genotypes) were evaluated under normal and regulated deficit irrigation for 3 years (2012–14) in the field. Irrigation was then withheld in 2015, and the genotypes were evaluated for post-drought recovery and persistence. The results showed that regulated deficit irrigation decreased forage yield, yield components, persistence and recovery. A broad range of general combining ability was observed for most of the measured traits. Moderate to high estimation of narrow-sense heritability for yield components, persistence, recovery and summer dormancy index indicated that phenotypic selection may be successful to attain genetic progress. Under deficit irrigation, flowering time was positively correlated with persistence and recovery, indicating that selection based on lateness would lead to improvement in these traits. Stable and superior families across environments were identified based on regression coefficients and principle component analysis that would be desirable in future breeding programs.

The consequences of recurrent drought events compared with a single drought, and drought's interaction with deliberate selfing compared with open‐pollination on postdrought recovery and persistence of smooth bromegrass, are not clear. This research was conducted to investigate the effects of recurrent drought stresses compared with a single drought on stress response, poststress recovery and persistence of full‐sib and half‐sib progenies of smooth bromegrass. During this study, 25 selfed (S1) and 25 open‐pollinated (OP) progenies of smooth bromegrass created in 2012 were evaluated in the field under normal and recurrent drought stress during 2013–2016. After the first harvest of above‐ground biomass in 2016, irrigation was withheld in both environments for 2 months; plants were subsequently re‐watered and evaluated. Recurrent drought stress changed the relationships between different traits. Moreover, prolonged drought stress resulted in increased plant productivity (recovery aerial biomass; RABI) of S1 and OP populations in recurrent drought stress compared with normal environment. Mandatory selfing increased persistence of smooth bromegrass genotypes but did not affect recovery after prolonged drought stress. Results revealed that, selecting among S1 families would be more effective than OP ones.