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

Main Conclusion
Seed 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.

Abstract
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 (ions), known to inhibit germination were tested in germination assays and their osmolality and conductivity assessed. 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 SEM. We found 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 to deliver improved commercial seed quality.