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Temperature is one the most influential environmental factors for the germination and establishment of grass species. The specific objective of this study was to determine the effects of low constant temperature on the time needed to express the full germination capacity of nondormant seedlots. Fifteen accessions, comprising seven of Lolium perenne L., three of Festuca arundinacea Schreb., three of Dactylis glomerata L. and two of Triticum aestivum L., were evaluated at constant temperatures of 5 and 21 °C. As expected, the germination rates were faster at 21 °C than at 5 °C. Indeed, at 5 °C seeds needed up to twenty-one times longer to reach the maximum germination than when tested at 21 °C. The genotypic variability found for the ratio of germination rates between the two temperatures (i.e., germination rate at 5 °C/germination rate at 21 °C) was much more variable than what is found in the literature for perennial cool-season grasses. On the other hand, in most cases, no significant differences were observed in the germinability (the capacity to germinate) response to 5 °C and 21 °C. Within the four species, twelve of the fifteen studied accessions expressed the same germinability at 5 °C and 21 °C, when given enough time. Only three accessions had final germination percentages higher at 21 °C than at 5 °C. Our results suggest that, in general, nondormant seeds at low temperatures germinate as well as nondormant seeds at near-optimal temperatures, provided they have enough time to express their germination capacity. These findings cast doubts on the validity of conclusions drawn in many studies where germination experiments were performed for a period insufficient to obtain full germination at low temperatures. Another major finding in this work concerns the risk of wrongly estimating germinability at low temperatures. [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]