Rain events at maturity severely impact the seed quality of psyllium (Plantago ovata Forssk)

Abstract

Plantago ovata Forssk. is an emerging crop yielding psyllium husk, a material com-prised of hydrophilic polysaccharides that form mucilage upon wetting. Psyllium husk has important industrial uses including as a dietary fibre supplement and a textural al-ternative in gluten-free bread production. Industrial applications require high-quality and purity psyllium husk, but consistent supply of uniform quality material is often limited by climatic constraints, especially unseasonable rainfall at crop maturity. Here we compared the seed quality of four P. ovata varieties harvested before and after 26 mm of rain and validated our key findings in the following season. Colourimetry showed that the rain event caused the seeds to be darker and greener, possibly from pigment oxidation and microbial growth. Sugar profiling, water absorption assays and microscopy showed that premature hydration of the husk in rain-damaged samples caused loss of the most soluble mucilage components and an increase in non- mucilage contaminants, leading to a reduction in seed water absorption capacity, which is a key indicator of psyllium husk functionality. Germination was also diminished in rain- affected seeds. In this study we show for the first time the extent that unseasonable rain at maturity has on P. ovata seed quality. We suggest that rain-damaged seeds are unsuitable for husk production and resowing and outline potential screening methods to identify rain-damaged seeds before purchase. Additionally, the extensive quality impacts described here may make P. ovata a suitable model or indicator species for studying acute climate effects on seed quality, especially from rain.