A Novel Phenotyping Technique for Reproductive-stage Salinity Tolerance in Rice☆

Abstract Rice responds differentially at different stages of development for salinity tolerance. Seedling and reproductive stages are the most sensitive growth stages; however, association between tolerances at the two stages is very weak, suggesting their regulation through different processes and sets of genes/QTLs. There are numerous reports on seedling-stage salinity tolerance in rice, but hardly on reproductive-stage salinity tolerance mainly because of the lack of reliable reproductive-stage-specific phenotyping. There are two major challenges, first, how to stress plants at the reproductive stage without stressing them at the seedling or late vegetative stage. Second, how to impose the stress on different genotypes or mapping populations at equivalent growth stages of development as they may mature differently. We devised a methodology that allows salt translocation to the reproductive organs such as the flag leaf (the largest source for the sink) and panicle as quickly as possible just at the initiation of booting when the genotypes are at the same stage of tissue/organ development rather depending on age of the plant. Extra leaves were clipped, leaving only a minimum number of leaves needed by the rice plant that will not significantly affect grain yield and yield components. Salt stress equivalent to EC 10 dSm -1 was imposed on rice plants with trimmed leaves starting from boot leaf emergence up to 20 days in a pot experiment under controlled conditions. The stage-specific effect of salt stress was verified by observing salt-sensitive and salt-tolerant genotypes. Leaf cutting before the booting stage efficiently directed the salt concentration to the reproductive stage and helped in discriminating tolerant genotypes from sensitive ones as evidenced by the lower pollen viability and higher accumulation of toxic ions in the flag leaf of the sensitive genotype (IR64). The opposite was found true for the tolerant genotype (IR4630-22-2-5-1-3). Details will be discussed during presentation.