Using seed respiration as a tool for calculating optimal soaking times for ‘on-farm’ seed priming of barley (Hordeum vulgare)

Javier Carrillo-Reche,Adrian C Newton,Richard S Quilliam

doi:10.1017/s0960258521000039

Javier Carrillo-Reche, Adrian C Newton + Show 1 more

Open Access

https://doi.org/10.1017/s0960258521000039

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Abstract

AbstractA low-cost technique named ‘on-farm’ seed priming is increasingly being recognized as an effective approach to maximize crop establishment. It consists of anaerobically soaking seeds in water before sowing resulting in rapid and uniform germination, and enhanced seedling vigour. The extent of these benefits depends on the soaking time. The current determination of optimal soaking time by germination assays and mini-plot trials is resource-intensive, as it is species/genotype-specific. This study aimed to determine the potential of the seed respiration rate (an indicator of metabolic activity) and seed morphological changes during barley priming as predictors of the priming benefits and, thus, facilitate the determination of optimal soaking times. A series of germination tests revealed that the germination rate is mostly attributable to the rapid hydration of embryo tissues, as the highest gains in the germination rate occurred before the resumption of respiration. Germination uniformity, however, was not significantly improved until seeds were primed for at least 8 h, that is, after a first respiration burst was initiated. The maximum seedling vigour was attained when the priming was stopped just before the beginning of the differentiation of embryonic axes (20 h) after which vigour began to decrease (‘over-priming’). The onset of embryonic axis elongation was preceded by a second respiration burst, which can be used as a marker for priming optimization. Thus, monitoring of seed respiration provides a rapid and inexpensive alternative to the current practice. The method could be carried out by agricultural institutions to provide recommended optimal soaking times for the common barley varieties within a specific region.

Highlights

Seed germination involves an array of coupled morphological and respiratory changes that make up three distinct phases each of which are characterised by the dynamics of water uptake
After the first 4 h of imbibition, the wetting of the embryonic tissues was visually evident. This was reflected in moisture content as almost half of the total water absorbed occurred within the first 4 h of soaking, which is characteristic of the phase I “imbibition” stage (Fig. 2a)
From 4 h to 20 h, no major morphological changes were observed, the overall seed size increased gradually concurrent with a progressive increase in moisture content

Summary

Introduction

Seed germination involves an array of coupled morphological and respiratory changes that make up three distinct phases each of which are characterised by the dynamics of water uptake.Germination commences with ‘imbibition’ (phase I), a profuse uptake of water by the dry seed and a gradual increase of seed size, this phase is associated with no or little metabolic activity (Bewley et al, 2013). By controlling the transition through the germination phases, i.e. allowing seeds to undergo the pre-germinative phases I and II but preventing the start of phase III, ‘on-farm’ primed seed retains the benefits of pre-germinative advancements and, concurrently, preserve desiccation tolerance (Harris, 2006; Bewley et al, 2013). This can lead to quicker emergence and enhanced seedling vigour (and yield) when the primed seed is sown in the field as demonstrated for a range of crops (Carrillo-Reche et al, 2018). To fully exploit this method of seed priming, the safe limit (the maximum length of time that seeds can be soaked without germination taking place before sowing) for each crop and cultivar first needs to be determined

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