Marker-Assisted Introgression of the Salinity Tolerance Locus Saltol in Temperate Japonica Rice

Abstract

Background Rice is one of the most salt sensitive crops at seedling, early vegetative and reproductive stages. Varieties with salinity tolerance at seedling stage promote an efficient growth at early stages in salt affected soils, leading to healthy vegetative growth that protects crop yield. Saltol major QTL confers capacity to young rice plants growing under salt condition by maintaining a low Na+/K+ molar ratio in the shoots. Results Marker-assisted backcross (MABC) procedure was adopted to transfer Saltol locus conferring salt tolerance at seedling stage from donor indica IR64-Saltol to two temperate japonica varieties, Vialone Nano and Onice. Forward and background selections were accomplished using polymorphic KASP markers and a final evaluation of genetic background recovery of the selected lines was conducted using 15,580 SNP markers obtained from Genotyping by Sequencing. Three MABC generations followed by two selfing, allowed the identification of introgression lines achieving a recovery of the recurrent parent (RP) genome up to 100% (based on KASP markers) or 98.97% (based on GBS). Lines with highest RP genome recovery (RPGR) were evaluated for agronomical-phenological traits in field under non-salinized conditions. VN1, VN4, O1 lines were selected considering the agronomic evaluations and the RPGR% results as the most interesting for commercial exploitation. A physiological characterization was conducted by evaluating salt tolerance under hydroponic conditions. The selected lines showed lower standard evaluation system (SES) scores: 62% of VN4, and 57% of O1 plants reaching SES 3 or SES 5 respectively, while only 40% of Vialone Nano and 25% of Onice plants recorded scores from 3 to 5, respectively. VN1, VN4 and O1 showed a reduced electrolyte leakage values, and limited negative effects on relative water content and shoot/root fresh weight ratio. Conclusion The Saltol locus was successfully transferred to two elite varieties by MABC in a time frame of three years. The application of background selection until BC3F3 allowed the selection of lines with a RPGR up to 98.97%. Physiological evaluations for the selected lines indicate an improved salinity tolerance at seedling stage. The results supported the effectiveness of the Saltol locus in temperate japonica and of the MABC procedure for recovering of the RP favorable traits.

Physiological Responses to Salt Stress at the Seedling Stage in Wild (Oryza rufipogon Griff.) and Cultivated (Oryza sativa L.) Rice

“…From a visual evaluation of symptoms of salt stress injuries, based on the SES score [35] used for mass screening (Figure 1A and Figure S1), OR showed higher survival rate and was the most tolerant genotype. On the contrary, between the two Italian cultivars, VN was the most sensitive, in accordance with previous results obtained in similar salt treatments under hydroponics [31,34].…”

“…Consequently, upon salt stress, the shoot/root fresh weight ratio remained almost unchanged in OR, whereas it decreased significantly in B and, to a higher extent, in VN (Figure 2B). Under analogous salt treatment, a similar high reduction in shoot/root fresh biomass ratio was observed in VN, and in the salt sensitive japonica Onice rice cultivar [34], while the tolerant indica IR64-Saltol cultivar kept this ratio almost constant. Shoot growth impairment and changes in biomass partitioning induced by salinity have been shown to be linked to variations in hormonal concentrations of auxins and cytokinins in roots and shoots [45].…”

“…In order to analyze the response to salt stress by rice at the seedling stage, rice seedlings were grown in hydroponic culture for 2 weeks; during the second week, seedlings were exposed to 80 mM NaCl, which is considered a suitable concentration for studying the salt tolerance of rice grown in hydroponics over this time interval [34].…”

QTLs and Genes for Salt Stress Tolerance: A Journey from Seed to Seed Continued

“…The amount of proline provides stress tolerance through the maintenance of cell osmotic balance and protection of cell membranes [ 137 ]. It is also involved in reserving organic N 2 during the stages of stress recovery in plants [ 138 , 139 , 140 ]. Therefore, the YNU31-2-4 population was suggested to be a promising candidate for the improvement of salt stress under both seedling and reproductive stages of rice cultivars for the maintenance of higher yields even in changing environmental conditions.…”

Homomorphic Integral and Dual Rectified Convolutional Grading for Salinity Prediction During Seedling in Rice

“…However temporal aspects were not covered. In [16], the temporal aspects involved in rice salinity employing genotyping and marker assisted backcross were analyzed. With this mechanism improved salinity stress at the seedling stage was ensured in an accurate and precise manner.…”