Rice growth, assimilate translocation, and grain quality in response to salinity under Mediterranean conditions

The effect of salinity on rice (Oryza sativa L.) cropping systems has been extensively studied in controlled experiments, but little is known about the performance of rice varieties to salt stress under field conditions. The study's purpose was to examine the effect of salinity on agronomic, physiological, and grain quality traits of indica and japonica rice varieties with different sensitivity to salt stress in a three-year (2010–2012) field study under Mediterranean conditions. Treatments consisted of two salinity levels, i.e., high salinity level (HSL, EC between 3.8 to 6.4 dS m-1) and low salinity level (LSL, EC between 0.9 and 1.3 dS m-1), and eight rice varieties arranged in a randomized complete block design in a split-plot arrangement. Rice growth showed an inconsistent response across varieties and years, demonstrating the importance of genotype and environment on rice response to salinity. The detrimental effect of salinity to rice growth was more evident when the weather conditions were favourable for rice production and salt stress was the main limiting factor for plant growth. Averaged across varieties, HSL prolonged the time to heading by 7 to 14 days compared to the LSL treatment. A considerable decrease of dry matter accumulation was observed in salt-sensitive varieties. In addition, salinity stress reduced the number of fertile tillers per plant up to 27% and the grain yield up to 50%. The contribution of pre-anthsesis assimilates to grain yield was increased due to salinity in two of the three years of the experimentation. In tolerant varieties, no differences among salinity levels in grain weight were observed. Salinity had less effect on grain quality. Grain length was similar across salinity treatments, while there was no consistent correlation between salinity level and grain vitreosity. Findings provide suggestive salinity tolerance traits of the studied rice varieties under field conditions that could be exploited for optimizing the performance of rice cropping systems in saline soils.