Evaluation of zeolite seed 'Drying Beads®' for drying rice seeds to low moisture content prior to long-term storage

Four experiments were carried out using zeolite seed Drying Beads (R) to dry freshly harvested rice seeds to low (genebank) moisture content. The beads were mixed with 120 g of seeds in different ratios (between 0 and 3 beads-to-seed, by weight), sealed inside moisture-proof bags or heat-sealed laminated aluminium foil packets and placed in temperature controlled environments for drying and/or storage. The first experiment confirmed that the beads dry seeds very rapidly. The final moisture content of the seeds depended on the ratio of beads to seeds and, to some extent, on the temperature, with slightly more drying at 30 degrees C compared with 15 or 5 degrees C. When seeds were stored with the beads at either 5 or -20 degrees C, seeds continued to dry. In the first two experiments, insufficient beads (bead-to-seed ratios of 0.97 and 1.06) were used to reach the target moisture content of 6.1%. The lowest moisture content reached was 4.2%, when the quantity of beads was three-times that of seeds. Germination was similar for seeds stored for 371 days at 5 degrees C either with or without the beads after the same initial drying treatment. There was lower germination of seeds dried at low temperature and then stored at -20 degrees C; however, this was attributed to dormancy. Whilst the water uptake isotherms confirmed the high capacity of the beads compared with silica gel, particularly at low relative humidity, the beads do not work to full capacity in a bead-seed system and the adsorption properties appeared to change. Further work is required to optimise the use of these beads for drying seeds to target moisture contents, without either under-drying which could lead to undesirable high rates of viability loss, or unnecessary and perhaps detrimental over-drying.