Unexpected Intraspecific Variability of Perennial Ryegrass (Lolium perenne L.) in Response to Constant Temperature During Germination and Initial Heterotrophic Growth

Abstract

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.

Tall Fescue (Festuca arundinacea Schreb.) Shows Intraspecific Variability in Response to Temperature during Germination

“…On top, under high temperature and humidity, saprophytic fungi developed that made it impossible to follow the seeds beyond twelve weeks. Consequently, a subsidiary experiment was conducted at 40 • C under aseptic conditions, as described previously [6].…”

“…As in Ghaleb et al [5], for each set of 100 seeds in a Petri dish, the cumulated number of germinated seed over time was fitted a nonrectangular hyperbola. From there, the parameters t 50% , τ, and α 50% were estimated as described in Ahmed and Escobar-Gutiérrez [6]. Further, for each accession, the data were normalized for its maximum germinability observed in any Petri dish, regardless of the temperature treatment [6].…”

“…From there, the parameters t 50% , τ, and α 50% were estimated as described in Ahmed and Escobar-Gutiérrez [6]. Further, for each accession, the data were normalized for its maximum germinability observed in any Petri dish, regardless of the temperature treatment [6]. The four replicates per accession were pooled together and plotted against the temperature [6].…”

“…By its effects on germination and seedling growth, temperature affects the recruitment of individuals and, consequently, the genetic diversity of plant communities. The rates of chemical and biochemical reactions, as well as the rates of cell growth and plant functioning, all depend on the temperature [6,7]. The relationship between seed germination and temperature has been extensively studied [2,8], and several mathematical models have been proposed to describe such a relationship that can be expressed in terms of the cardinal temperatures [9][10][11][12].…”

“…However, as for many other species, published knowledge is scarce concerning the intraspecific variability of tall fescue in response to climate factors, particularly to temperature during germination and early growth [7]. Despite numerous studies having explored the relation between temperature and germination in gramineous grasslands [18][19][20][21][22][23][24], there have only been a few reports on within-species genetic diversity [5,6,9,25,26]. For instance, the germination percentage was shown to display very different temperature responses for cocksfoot accessions [9,27,28].…”