Abstract
Various adaptive mechanisms can ensure that seedlings are established at the most favourable time and place. These mechanisms include seed dormancy i.e., incapacity to germinate in any environment without a specific environmental trigger and inhibition i.e., incapacity to germinate in an unfavourable environment (water availability, temperature: thermoinhibition and light). The objective of this research was to study in the temperate range for germination of forage and turf grass species perennial ryegrass, if the thermal requirements for germination are under genetic controlled and could be selectively bred. Two divergent selections of three cycles were realized on a natural population: one to select for the capacity to germinate at 10°C vs. the impossibility to germinate at 10°C, and one to select for the capacity to germinate at 32°C vs. the impossibility to germinate at 32°C. Seeds of all the lots obtained from the two divergent selections were then germinated at constant temperatures from 5 to 35°C to evaluate their germination ability. Concerning the positive selection, the first cycle of positive selection at 10°C was highly efficient with a very strong increase in the germination percentage. However, afterward no selection effect was observed during the next two cycles of positive selection. By contrast, the positive selection at 32°C was efficient during all cycles with a linear increase of the percentage of germination at 32°C. Concerning the negative selection, we observed only a large positive effect of the first cycle of selection at 10°C. These findings demonstrate that seed thermoinhibition at 10 and 32°C observed in a natural population of perennial ryegrass has a genetic basis and a single recessive gene seems to be involved at 10°C.
Highlights
As the first stage of the plant life cycle, germination is critical for successful establishment and growth of plants (Ooi, 2012; Nunes et al, 2016)
In order to better assess the effect of selection, the germination capacity of the different populations resulting from the selection and the initial population, was evaluated in the range of temperatures from 5 to 35◦C
This experimental study showed clearly that the ability to germinate at specific unfavourable temperatures could be selectively bred within a natural population of perennial ryegrass
Summary
As the first stage of the plant life cycle, germination is critical for successful establishment and growth of plants (Ooi, 2012; Nunes et al, 2016). Various adaptive mechanisms ensure that seed germination occurs at the most advantageous time and place. These mechanisms could be classified as (i) “dormancy” that requires a special event or “trigger” before the embryo can resume growth e.g., stratification by cold temperatures and (ii) “inhibition” that requires just favourable environmental conditions for the embryo to grow (Hills and van Staden, 2003; Batlla and Benech-Arnold, 2015). For some dormant seeds, special environmental conditions must be met to release this dormancy and additional conditions must be met to allow germination of the seeds (Baskin and Baskin, 1988; Simpson, 1990; Bewley, 1997; Bewley et al, 2013). The action of temperature on seed germination is related to enzyme activity and membrane stability and permeability affecting respiratory metabolism (Baskin and Baskin, 2014; Nunes et al, 2016)
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