Abstract
Rice is the staple food for almost half of the world population. In South and South East Asia, about 40% of rice production is from deltaic regions that are vulnerable to salt stress. A quantitative approach was developed for characterizing genotypic variability in biomass production, leaf transpiration rate and leaf net photosynthesis responses to salinity during the vegetative stage, with the aim of developing efficient screening protocols to accelerate breeding varieties adapted to salt-affected areas. Three varieties were evaluated in pots under greenhouse conditions and in the field, with average soil salinity ranging from 2 to 12dSm−1. Plant biomass, net photosynthesis rate, leaf transpiration rate and leaf conductance were measured at regular intervals. Crop responses were fitted using a logistic function with three parameters: 1) maximum rate under control conditions (Ymax), 2) salinity level for 50% of reduction (b), and 3) rate of reduction (a). Variation in the three parameters correlated significantly with variation in plant biomass production under increasing salinity. Salt stress levels that caused 50% reduction in net leaf photosynthesis and transpiration rates were higher in the tolerant genotype BRRI Dhan47 (16.5dSm−1 and 14.3dSm−1, respectively) than the sensitive genotype IR29 (11.1dSm−1 and 6.8dSm−1). In BRRI Dhan47, the threshold beyond which growth was significantly reduced was above 5dSm−1 and the rate of growth reduction beyond this threshold was as low as 4% per unit increase in salinity. This quantitative approach to screening for salinity tolerance in rice offers a means to better understand rice growth under salt stress and, using simulation modelling, can provide an improved tool for varietal characterization.
Highlights
Salinity is one of the main limiting environmental factors for crop production worldwide
At a high salinity level of 12 dS m−1, no significant differences in biomass were observed among the contrasting rice genotypes evaluated in this study, indicating that even the tolerant genotype was overwhelmed due to both osmotic stress and higher accumulation of salt in plant tissues, causing both toxicity and internal dehydration
For the tolerant genotype BRRI Dhan47, a 50% loss in leaf conductance did not occur until a salinity level of 11.08 dS m−1, but BRRI Dhan47adjusted its stomatal conductance at a lower level than the other genotypes (1.04 dS m−1)
Summary
Salinity is one of the main limiting environmental factors for crop production worldwide. Its occurrence and severity are expected to increase by around 25% by 2050 in vulnerable regions, in deltaic costal zones (Dasgupta et al, 2014) where rice growing areas account for more than 65% of global production, making salinity one of the major threats to food security. Salinity has different effects on yield and growth, depending on crop stage, stress severity and duration, as well as the tolerance of the variety (Lutts et al, 1995; Zeng and Shannon, 2000). Addressing salt stress by developing improved salt-tolerant rice cultivars could mitigate the effects of salinity on rice production and contribute to improving food security at a global scale
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