Breeding of perennial ryegrass (Lolium perenne L.) for forage is mainly aimed at increase in herbage yield. However, abiotic stresses such as drought and winterkill threaten persistence and ability to produce stable aerial biomass of the plant. Field experiments, performed under natural conditions, rather than dissection of abiotic stress factors under artificial or semiartificial conditions, offers opportunity to evaluate the effect of complex of abiotic stresses on the plant performance. The aim of this study was to evaluate the relationship between dry matter yield and tolerance to winter kill and drought of perennial ryegrass ecotypes and cultivars differing in their ploidy level during a 2‐yr period. The field experiment was located in Akademija, Lithuania (55°40′ N, 23°87′ E) in 2015 and 2016. The germplasm consisted of 128 diploid and 25 tetraploid perennial ryegrass populations. Winterkill, spring growth and regrowth after cuts, drought damage, and dry matter yield were assessed. Short periods of lower than −10°C temperatures with slim snow cover determined low damages of the perennial ryegrass after winters. Medium correlation was estimated between drought damages and dry matter yield. Tetraploid genotypes of perennial ryegrass demonstrated higher tolerance to cold and drought stress conditions, better spring growth and regrowth after cuts, and higher dry matter yield.

Drought is one of the critical abiotic stresses that significantly affect agricultural production, and current models predict an increase in its severity and intensity in the future. Generally, polyploidy has been found to improve the resistance of plants to abiotic stress. Understanding the role of ploidy in resistance to drought was achieved by comparing the response between diploids and their respective induced autotetraploids of Westerwolths ryegrass (Lolium multiflorum ssp. multiflorum). Field trials were carried out in the 2017 and 2018 growing seasons, and mild drought simulation experiments in controlled conditions were carried out to validate the effect of chromosome duplication. Results obtained from morphological traits in the field experiment revealed that the induced tetraploids were significantly (p < 0.05) taller, had longer inflorescences and larger flag leaf area than their diploid counterparts, especially in the year 2018 characterized by the prolonged drought. This study also revealed that the induced tetraploids produced more dry matter yield than their diploid progenitors, especially in drought periods. The induced tetraploids had significantly higher antiradical activity and phenolic content than the diploid progenitors in response to mild drought, and this significantly correlated with the plant performance in 2018 field trials, indicating that increased ploidy level plays an important role in conferring resistance to drought in Westerwolths ryegrass. Furthermore, the antiradical activity and total phenolic content proved to be a good tool to evaluate drought tolerance at the vegetative stage in Westerwolths ryegrass.

Global warming is predicted to impact many agricultural areas, which will suffer from reduced water availability. Due to precipitation changes, mild summer droughts are expected to become more frequent, even in temperate regions. For perennial ryegrass (Lolium perenne L.), an important forage grass of the Poaceae family, leaf growth is a crucial factor determining biomass accumulation and hence forage yield. Although leaf elongation has been shown to be temperature-dependent under normal conditions, the genetic regulation of leaf growth under water deficit in perennial ryegrass is poorly understood. Herein, we evaluated the response to water deprivation in a diverse panel of perennial ryegrass genotypes, employing a high-precision phenotyping platform. The study revealed phenotypic variation for growth-related traits and significant (P &lt; 0.05) differences in leaf growth under normal conditions within the subgroups of turf and forage type cultivars. The phenotypic data was combined with genotypic variants identified using genotyping-by-sequencing to conduct a genome-wide association study (GWAS). Using GWAS, we identified DNA polymorphisms significantly associated with leaf growth reduction under water deprivation. These polymorphisms were adjacent to genes predicted to encode for phytochrome B and a MYB41 transcription factor. The result obtained in the present study will increase our understanding on the complex molecular mechanisms involved in plant growth under water deficit. Moreover, the single nucleotide polymorphism (SNP) markers identified will serve as a valuable resource in future breeding programs to select for enhanced biomass formation under mild summer drought conditions.

Winter hardiness is influenced by many environmental factors, and freezing tolerance is among the main ones, rendering the phenotypic selection of winter wheat (Triticum aestivum L.) under field conditions a difficult task due to the irregular occurrence or absence of winter damage in field trials. Plant growth in response to low temperatures during the acclimation period might be used as an indirect approach to assess freezing tolerance. Thirteen winter wheat cultivars were investigated for autumn and spring growth and winter hardiness under field conditions for two growing seasons. Additionally, a precise and non-destructive technique was applied to study leaf growth at a high temporal resolution accompanied by a freezing tolerance test under laboratory and semi-field conditions. The results of the study revealed variations in thermal growth patterns among the 13 winter wheat cultivars. The cultivars with the lower base temperature (Tb) values, in particular ‘Lakaja DS’ and ‘Sedula DS’, grew slower and, thus, had a lower response to temperature increases (SlpLER-T) than the fast-growing cultivars, such as ‘Simano” and ‘KWS Ferrum’, whose SlpLER-T values were stronger and whose Tb values were higher. A correlation analysis of the investigated traits showed a clear association between leaf growth parameters and freezing tolerance, indicating a certain level of genetic adaptation to growth cessation under low temperatures, and which confirmed that these are important factors for explaining the freezing tolerance of different cultivars. The evaluated freezing tolerance (LT30) showed a strong negative correlation (r = −0.82 ÷ −0.89, p = 0.01) to winter hardiness scores from the field experiment, supporting the essential contribution of growth rate patterns to winter hardiness. The findings provide novel information for the development of winter-hardy wheat cultivars that are adapted to the future environments.

Perennial ryegrass is an important agricultural crop, however, it is susceptible to winterkill. Freezing injury is caused primarily by ice formation. The LpIRI1 protein has the potential to inhibit ice recrystallization, thus minimize the damage. An association study was conducted using single nucleotide polymorphisms obtained through allele sequencing of the LpIRI1 gene and phenotypic data were collected using two phenotyping platforms in a perennial ryegrass association mapping population of 76 diverse genotypes. Winter survival (FWS) was evaluated under field conditions, while tiller survival (PTS) and electrolyte leakage (EL) at -8 and -12°C were determined under controlled-environment conditions. Proline content (PC) in cold-acclimated plants was measured prior to the freezing test. Significant variation in FWS, PTS, EL and PC was observed among genotypes in our panel. EL and PTS revealed significant negative correlations at -8°C (r s = -0.40) and -12°C (r s = -0.49). PC, however, did not show significant correlations with any of the measured traits, while FWS was correlated (r s = -0.48) with EL at -12°C. The LpIRI1 gene was found to be highly polymorphic with an average SNP frequency of 1 SNP per 16 bp. Association analysis revealed two non-synonymous SNPs being associated with increased EL, both located in the LpIRI1 leucinerich repeat. The results indicate that allelic variation in the LpIRI1 gene plays an important role in the cell membrane integrity of perennial ryegrass during freezing, and can be exploited for developing more freezing tolerant cultivars.