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Tall fescue is a major species growing in temperate grasslands. It is a cool-season perennial native of Western Europe and used worldwide as forage for its quality and adaptability to various soils and climates. By its effects on germination and seedling growth, temperature affects the recruitment of individuals and, consequently, the genetic diversity of plant communities. Under most climate change scenarios, breeding cultivars adapted to new ranges of temperature will be necessary. Knowing the variability of the responses to temperature by different accessions is an essential first step towards such breeding. In this work, we (i) analyze the intraspecific variability of tall fescue in response to a constant temperature during germination and (ii) quantitatively describe the response curves. A sample of nine, from 128, accessions of tall fescue was evaluated. Four replicates of 100 seeds per accessions were tested for germination in the dark at eight constant temperatures ranging from 5 to 40 °C with increases of 5 °C. The germinability, lag to start and maximum germination rates were estimated. It was observed that the responses of tall fescue accessions were statistically different (p < 0.05). The optimal temperature for maximum germination ranged from 9 °C to 25 °C. Germination was not observed for any accession at 40 °C. The novelty of this work comes from the duration of the sampling period at low temperatures that was longer than in most published papers. Based on the responses to temperature during germination, our findings suggest that a high intraspecific genetic variability exists in tall fescue that merits further exploration. This variability should be useful to breed new cultivars adapted to the new environmental conditions imposed by the ongoing fast climate change. [ABSTRACT FROM AUTHOR]

Lolium perenne (L.) is one of the most important species in temperate grasslands. Temperature is a major factor controlling plant development. Breeding L. perenne cultivars adapted to new ranges of temperature could be necessary under most climate change scenarios. However, before any breeding effort in such direction, knowing the intraspecific variability of responses to temperature is essential. Our objective was to analyze a sample of accessions of L. perenne for their response to constant temperature during germination and initial heterotrophic growth. Eight accessions were taken out from a genebank containing 160 accessions. Six accessions were wild populations collected in different places in France and the other two were populations from a selection program. For germination, four replicates of 100 seeds per accession were tested in Petri dishes in the dark at eight constant temperatures, from 5 to 40°C with increases of 5°C. Germination countings were carried out at variable time intervals and durations that depended on treatments. For initial heterotrophic growth analysis, seeds were germinated at 25°C. Sets of 30 seedlings per accession were placed in polypropylene boxes on blotter blue paper and transferred to each one of the eight treatments in the dark. They were pictured at variable time intervals for root and shoot growth measurement by image analysis. Neither seed germination nor heterotrophic growth was observed at 40°C, for any accession. Temperature and time course response surfaces were markedly different between accessions. Equally, maximum germinability and the shape of the response curves to temperature were significantly different between accessions. This means that limited similarities between responses were observed. Furthermore, germination rates followed the non-linear beta function with significant differences between some accessions. These also showed significant differences in their root and shoot growth rate in response to temperature. In general, the relative growth rates of roots and shoots were slow at 5°C, peaked between 25 and 30°C, and showed a sharp reduction afterward. These results reveal, for the first time, high genetic variability within L. perenne germplasm for the response to temperature in the initial life phases. This discovered variability should serve breeders to create perennial ryegrass varieties for the future. [ABSTRACT FROM AUTHOR]