Determination of the appropriate level of salinity for screening of hydroponically grown rice for salt tolerance

Abstract

Development of salt tolerant rice varieties has become an urgent priority because of the increase of salinity in rice lands. The objectives of the present experiment were to determine: (a) the appropriate level of salt stress to be imposed for screening rice varieties grown in hydroponics for salt tolerance at Phase I (osmotic stress) and at Phase II (salt ion toxicity) of salt stress development; (b) the point of transition from Phase I to II and (c) the degree of salt tolerance in the Sri Lankan improved rice variety At354 in comparison to the known salt-tolerant rice variety, Pokkali. Seedlings of the two varieties were grown in a plant house in nutrient solutions in a range of salt concentrations, i.e. 1 (Control), 20, 40, 60, 80, 100, 120 and 150 mM NaCl. Area of the youngest fully-expanded leaf at salt stress commencement and at 2-7 day intervals was measured non-destructively. The total plant biomass was measured after 30 days of salt stress. Based on the time courses of relative area of the youngest fully-expanded leaf RL A (i.e. area of the leaf under salt stress as a proportion of that in the control), 100 mM Na + was determined as the optimum salinity level for varietal screening. At 100 mM Na + , the two phases could be identified clearly, with Phase I (from 0 to 10 days after reaching 100 mM Na + ) showing a significantly lower rate of reduction of RL A than Phase II (starting after 10 days). The Sri Lankan improved rice variety At354 showed lower rates of reduction of relative plant biomass and RL A and a slower rate of Na + accumulation in the shoot in comparison to Pokkali with increasing salt stress, demonstrating its greater salt tolerance than that of Pokkali.

Screening eighty traditional and improved rice genotypes in Sri Lanka for salinity tolerance at the seedling stage in Yoshida solution 

“…Dahanayaka et al (2015) reported that Pokkali5556 is salinity tolerant, and Noorzuraini et al (2021) reported that two different Pokkali lines (accession numbers were not given) are salinity tolerant. Pokkali has been reported as salinity tolerant at the seedling stage (Heenan et al, 1988;Wijerathna et al, 2011;de Costa et al, 2012b;Senanayake et al, 2017) and the panicle stage (Heenan et al, 1988). Pokkali serves as the tolerant check variety for salinity tolerance studies (El-Shabrawi et al, 2010;Chunthaburee et al, 2016;Sampangi-Ramaiah et al, 2020).…”

Assessment of Marker Based Genotype Diversity of Saltol QTL in Relation to Seedling Stage Salinity Tolerance in Selected Rice Genotypes

“…Salinity is a major constraint to expanding rice cultivation in Sri Lanka. Nearly 70% of the coastal rice lands are reported to be affected by salinity (De Costa et al, 2012). Sirisena and Herath (2009) stated that salinity is gradually spreading in rice lands of Sri Lanka both in coastal and inland regions.…”

Identification of Sri Lankan rice varieties having osmotic and ionic stress tolerance during the first phase of salinity stress

“…There were two salt treatments as 1 mM NaCl (un-stressed control) and 100 mM NaCl (salt-stress). Previous work as reported by De Costa et al (2012) showed 100 mM Na + to be the optimum level of salt stress for screening rice germplasm for salt tolerance during the two phases of salt stress development. The experimental design was a completely randomized design with two replications.…”

“…In order to ensure that plant growth is measured during Phase I of salt stress development, as determined by De Costa et al (2012), growth was measured 24 h after increasing the salinity up to 100 mM NaCl. Areas of the youngest fully expanded leaf and the next expanding leaf on the main culm were measured nondestructively in the control and salt-stressed treatments.…”

“…Plants were grown hydroponically in aerated nutrient solutions (Yoshida et al, 1972). In all 10 rounds of experiments, seed germination, preparation of nutrient solutions and seedling establishment and plant management were done using the protocol described in De Costa et al(2012). Briefly, seeds were germinated with moist filter paper and transferred to ¼ strength nutrient solutions in 3 L pots 01 wk after germination.…”