LAUSR

Low soil moisture is a major abiotic stress wide spread in arid and semi-arid regions, limiting both seed germination and seedling establishment. Deep-seeding technique allows seeds to use the moisture in deep soil, however, most sorghum seeds cannot penetrate soil layer of 10 cm or deeper. To develop sorghum varieties tolerant to deep-seeding, it is necessary to identify promising accessions with good agronomic traits and tolerance to deep-seeding. A high throughput hydroponic method was developed to screen sorghum accessions with long mesocotyl under dark conditions. This method revealed large genetic variations for mesocotyl length in the panel of 105 sorghum accessions, which were validated by soil culture and deep-seeding experiments. The lines with long mesocotyl under hydroponic culture had good seedling establishments in deep-seeding experiments, while the lines with short mesocotyl length could not emerge. Compared to conventional sand or soil cultural methods, the hydroponic culture was highly efficient that requires less time, space, and labor. The mesocotyl lengths of screened sorghum accessions under the newly developed hydroponic method were highly correlated with soil culture and germination rate under deep-seeding in soil. As an efficient screening tool for the mesocotyl lengths under soil culture and the seedling emergence rates from deep soil layer, the hydroponic culture method can be easily integrated in breeding programs targeting deep-seeding tolerance. Breeding for long mesocotyl sorghum varieties may lead to good seedling establishments under arid and semi-arid regions.