Salinity tolerance in Australian wild Oryza species varies widely and matches that observed in O. sativa.

backgroundSoil salinity is widespread in rice-producing areas globally, restricting both vegetative growth and grain yield. Attempts to improve the salt tolerance of Asian rice, Oryza sativa-the most salt sensitive of the major cereal crops-have met with limited success, due to the complexity of the trait and finite variation in salt responses among O. sativa lines. Naturally occurring variation among the more than 20 wild species of the Oryza genus has great potential to provide breeders with novel genes to improve resistance to salt. Here, through two distinct screening experiments, we investigated variation in salinity tolerance among accessions of two wild rice species endemic to Australia, O. meridionalis and O. australiensis, with O. sativa cultivars Pokkali and IR29 providing salt-tolerant and sensitive controls, respectively.

resultsRice plants were grown on soil supplemented with field-relevant concentrations of NaCl (0, 40, 80, and 100 mM) for 30 d, a period sufficient to reveal differences in growth and physiological traits. Two complementary screening approaches were used: destructive phenotyping and high-throughput image-based phenotyping. All genotypes displayed clear responses to salt treatment. In the first experiment, both salt-tolerant Pokkali and an O. australiensis accession (Oa-VR) showed the least reduction in biomass accumulation, SES score and chlorophyll content in response to salinity. Average shoot Na

conclusionThe combination of our two screening experiments uncovered striking levels of salt tolerance diversity among the Australian wild rice accessions tested and enabled analysis of their growth responses to a range of salt levels. Our results validate image-based phenotyping as a valuable tool for quantitative measurement of plant responses to abiotic stresses. They also highlight the potential of exotic germplasm to provide new genetic variation for salinity tolerance in rice.