Phenotypic Responses of Oryza Species to Saline Condition at Reproductive Growth Stage

Aims: This research aimed at evaluating the response and morphological effects of salt stress on Oryza species at vegetative and reproductive growth stage.

Study Design: Salt tolerance was evaluated by adopting the Standard Evaluation System of IRRI for salt tolerance under modified hydroponic systems.

Place and Duration of Study: The investigations for this study were conducted at AfricaRice Station at the International Institute of Tropical Agriculture (IITA), Ibadan (Latitude 3°541N and longitude 7°301W), Nigeria and the Department of Biological Sciences, Ahmadu Bello University, Zaria, Nigeria.

Methodology: Forty rice (Oryza sativa (20), Oryza glaberrima (10) Oryza barthii (05) and NERICA (05) genotypes encompassing 20 tolerant and 20 susceptible pre-screened genotypes to salinity stress at seedling growth stage were subjected to salinity stress at early vegetative growth stage. The sensitive (IR29) and tolerant (POKKALI) checks served as controls for susceptibility and tolerance respectively. These genotypes were subjected to salinization with NaCL at EC 8dsm-1 at pH 5.2 till maturity. Plant phenotypic responses were evaluated to ascertain specie response.

Results: Results acknowledged that the effect of salinity on plant growth was genotype and specie dependent. The interactions between genotypes and traits evaluated were highly significant (P< 0.01). Tolerance at seedling stage did not culminate to tolerance at reproductive stage. Phenotypic response to salinity stress at reproductive stages showed strong (p<0.01) negative association between salinity evaluation score (SES) to plant height (r2= -0.5), culm length (r2= -0.5) and filled grain (r2 = -0.5). Salinity stress adversely affected panicle emergence and caused aborted spikelet, thus suppressing rice yield. The grain length of susceptible genotypes increased significantly. A 55% increase in brown rice shape was obtained. Tolerance range for survival at reproductive stage for Oryza sativa and Oryza glaberrima were 90 and 40% respectively. Oryza barthii and NERICA were most susceptible to salt stress and failed to set seed at reproductive stage. Six (15%) genotypes showed tolerance comparable to the tolerant check at maturity while 7 (17.5%) genotypes were moderately tolerant to salinity. Six susceptible genotypes (15%) with an SES score of 7 at reproductive stage set seed.

Conclusion: The effect of salinity stress on plant growth and yield were genotype and specie dependent. Salinity adversely resulted in reductions in plant biometrics. Degrees of growth plasticity were observed in some genotypes as an escape strategy against salinity. Salt stress induced changes in grain lengths and seed shape. The presence of flag leaf and penultimate leaf or few leaves before panicle initiation determind the genotype ability to set seed at reproductive growth stage.