The biochemistry underpinning industrial seed technology and mechanical processing of sugar beet

James E. Hourston,Tina Steinbrecher,Gerhard Leubner-Metzger,Uwe Fischer,Michael Ignatz,Juliane Meinhard,Miroslav Strnad,Veronika Turečková

doi:10.1007/s00425-019-03257-5

Abstract

Main conclusionSeed-processing technologies such as polishing and washing enhance crop seed quality by limited removal of the outer layers and by leaching. Combined, this removes chemical compounds that inhibit germination.Industrial processing to deliver high-quality commercial seed includes removing chemical inhibitors of germination, and is essential to produce fresh sprouts, achieve vigorous crop establishment, and high yield potential in the field. Sugar beet (Beta vulgaris subsp. vulgaris var. altissima Doell.), the main sugar source of the temperate agricultural zone, routinely undergoes several processing steps during seed production to improve germination performance and seedling growth. Germination assays and seedling phenotyping was carried out on unprocessed, and processed (polished and washed) sugar beet fruits. Pericarp-derived solutes, known to inhibit germination, were tested in germination assays and their osmolality and conductivity assessed (ions). Abscisic acid (ABA) and ABA metabolites were quantified in both the true seed and pericarp tissue using UPLC-ESI(+)-MS/MS. Physical changes in the pericarp structures were assessed using scanning electron microscopy (SEM). We found that polishing and washing of the sugar beet fruits both had a positive effect on germination performance and seedling phenotype, and when combined, this positive effect was stronger. The mechanical action of polishing removed the outer pericarp (fruit coat) tissue (parenchyma), leaving the inner tissue (sclerenchyma) unaltered, as revealed by SEM. Polishing as well as washing removed germination inhibitors from the pericarp, specifically, ABA, ABA metabolites, and ions. Understanding the biochemistry underpinning the effectiveness of these processing treatments is key to driving further innovations in commercial seed quality.

Highlights

After the harvest of dry fruits and seeds, innovative industrial technologies such as cleaning, sizing, washing, drying, dehulling, polishing, priming, coating, or pelleting are applied (Sliwinska et al 1999; Kockelmann and Meyer 2006; Sharma et al 2009; Pedrini et al 2017; Steinbrecher and Leubner-Metzger 2017; Chomontowski et al 2019)
For commercial seed production, washing, dehulling, and polishing technologies are used to improve the germination performance by removing physical (“hardness”) and chemical constraints conferred by the seed and fruit coats
The true seed is composed of a fragile and brittle seed coat covering the coiled embryo which is curled around the central perisperm, a starchy storage tissue descended from the nucellus (Fig. 1a)

Summary

Introduction

After the harvest of dry fruits and seeds, innovative industrial technologies such as cleaning, sizing, washing, drying, dehulling, polishing, priming, coating, or pelleting are applied (Sliwinska et al 1999; Kockelmann and Meyer 2006; Sharma et al 2009; Pedrini et al 2017; Steinbrecher and Leubner-Metzger 2017; Chomontowski et al 2019). Processing technologies are applied to dry seeds and fruits for the production of fresh sprouts of Beta vulgaris subsp. In sugar beet, red beet, spinach, and other Amaranthaceae food and feed crops, the harvested “seed” is botanically a fruit, consisting of the true seed surrounded by the fruit coat (pericarp), derived from the carpels, and the incorporation of other parts of the flower (Artschwager 1927; Hermann et al 2007; Lukaszewska and Sliwinska 2007; Deleuran et al 2013). The germination of sugar beet is largely controlled by the pericarp, which functions as both a physiochemical barrier and a reservoir of inhibitory substances

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Conclusion