Identification of salt-tolerant wild Oryza : physiological and molecular investigation

Abstract

Soil salinity is a major abiotic stress constraining global crop production. Salinity is already affecting more than 800 million hectares (Mha) of total global land area, where 20 Mha and 4 Mha are in Australia and India, respectively. Salinity stress is thought to be only secondary to the drought stress in hindering rice productivity in the major rice-growing regions. Rice (Oryza sativa L.) is highly susceptible to salinity stress. Improvement in rice salinity tolerance using existing cultivars is facing bottlenecks of narrow genetic diversity and negative linkage between key salinity tolerance traits and yield and quality traits. Wild rice preserved wide diversity of genetic pools in undisturbed natural habitats, which draws a lot of attention from the plant breeders for its outstanding performance under different environmental stresses including salinity. In this Ph.D. thesis, salinity tolerance of ten Oryza species was explored using agronomical, physiological, and molecular approaches to expand the understanding of salinity tolerance in rice. I studied the agronomic, physiological, electrophysiological, and molecular responses of three rice cultivars (Koshihikari, Doongara, and Reiziq) differing in salt tolerance to NaCl treatment in both greenhouse and field experiments. The assessment was also conducted in the wild Oryza species to evaluate if the observed relation between salinity tolerance and the measured parameters in O. sativa, can also be validated in wild Oryza species. I then studied the adaptation mechanism of leaf tissue of the only halophytic Oryza species - O. coarctata and evaluated whether different leaf tissues of O. coarctata had a specific contribution to the overall tissue tolerance to NaCl using physiological, cell biological, and transcriptomic approaches. This study provides useful insights into physiological and molecular mechanisms of salinity response in the Oryza genus. I also suggest the potential use of traits and genes from wild rice species, especially those with the C genome and the halophyte O. coarctata, in breeding for salt-tolerant rice cultivars. Outcomes of this Ph.D. project will not only improve the understanding of the complex salt tolerance mechanisms in wild and cultivated rice species but also guide future research towards a more sustainable rice production by improving tolerance of cultivated rice with the salt-tolerant traits of their wild relatives.

Date of Award	2022
Original language	English