Phenotypic Response of Oryza Species Seedlings to Saline Conditions

Aims: This investigation was conducted to profile and evaluate the response of Oryza species to salt stress at seedling growth stage.

Study Design: Salt tolerance was studied by evaluations, using the Standard Evaluation System of IRRI for salt tolerance under hydroponic systems.

Place and Duration of Study: The investigations for this study were conducted at the International Institute of Tropical Agriculture (IITA), Ibadan (Latitude 3°541N and longitude 7°301W), Nigeria. The seeds of 184 rice genotypes (comprising of 130 O. sativa lines; 26 O. glaberrima, 16 O. barthii lines and 12 interspecific hybrids (NERICA) were obtained from the International Rice Research Institute, Las Boanos, Philippines and Africa Rice, Ibadan station, IITA, Nigeria.

Methodology: A total of 184 rice genotypes (comprising of 130 Oryza sativa lines; 26 Oryza glaberrima, 16 Oryza barthi and 12 interspecific hybrid (NERICA) were subjected to salinization with NaCl at EC 12dSm-1and pH 5.2 for 28 days in a hydroponic system. Plant phenotypic responses were evaluated to ascertain specie response. Among the test entries were Pokkali and IR29 which served as the tolerant and susceptible checks respectively.

Results: Seedlings from the genotypes showed varying levels of salt injury symptoms. The effect of salinity stress on plant growth parameters were genotype and species dependent. Progressive reductions in most growth parameters were obtained with increasing age of plant. Plasticity due to salinity stress was observed in some growth parameters (increased leaves number, longer root length and improved tillering ability). Susceptible genotypes showed more effect of salt injury than tolerant genotypes. Tolerant genotypes (6.92%) to salinity tress were predominated by Oryza sativa genotypes. The interspecific hybrids (NERICA) showed moderate tolerance (73.3%) to salinity stress followed sequentially by Oryza sativa (57.9%), Oryza glaberrima (18.5%) and Oryza barthii (12.5%). NERICA accumulated more salts in their shoot compared to other species of rice. TOG9047 (O. glaberrima) showed tolerance comparable to Pokkali (tolerant check) at seedling stage. Genotypes like OS6, Indiano and WAB 100-B-B-B-2B showed greater salt injury compared to IR29 (negative check) and could serve as an alternative to IR29. Reductions in biomass arising from salinity stress served as a good indicator of susceptible genotypes to salt stress. Reductions in the root/shoot ratio indicated that salinity had more effect on the roots than the shoots of the genotypes and hence, suggests the point of action and damage due to salinity.

Conclusion: Oryza species showed varied response to salt stress. These responses were genotype and specie dependent. Oryza sativa contained the highest percentage of tolerant genotypes to salinity stress at 12dSm-1. However, NERICA contained the highest percentage of moderately tolerant to salinity stress followed sequentially by Oryza sativa, Oryza glaberrima and Oryza barthii. Tolerant and moderately tolerant genotypes could further be exploited for breeding purposes geared towards crop advancement.