Silicon alleviation of ferrous iron toxicity in rice : a physiological and genetic approach

Ferrous iron (Fe2+) toxicity is one of the major abiotic stress factors in rice that contributes to yield losses worldwide. The beneficial effects of Silicon (Si) in tolerance to metal toxicity, mainly in Si-accumulating species have been already shown. Rice is a Si accumulator and the question of the Si effects on the reduction of iron toxicity has been raised. The general objective of this thesis was to determine the relationship between Si nutrition and stress induced by an excess of Fe2+ in cultivated rice in a perspective of genetic improvement. Firstly, the experiments were conducted in hydroponics in order to understand the mechanisms involved in Si-mediated alleviation of Fe2+ toxicity. Secondly, the physiological and agronomic effects of Si fertilization were assessed in the field under Fe2+ toxicity. Finally, the genetic determinism of tolerance mechanisms to Fe2+ toxicity induced by the presence of Si was studied through three practical approaches under hydroponic, pot and field conditions in a perspective of genetic improvement. The results of this PhD thesis showed that Si alleviates Fe2+ toxicity in rice. Firstly, Si readily accumulates in the aerial parts of the plant in form of phytoliths that contribute to limit transpiration and therefore decreases the translocation of Fe2+ to the leaves. Secondly, Si does not act directly on the antioxidant defense system of rice, but the oxidative stress in alleviated through the reduction in iron concentration in the leaf tissue. In the field, the leaf biomass increased, the symptoms of leaf bronzing were reduced and a 21 % yield increase was observed. In the perspective of plant improvement, 10 interesting genomic regions containing QTLs potentially involved in the mechanism of resistance to Fe2+ toxicity in the presence of Si were found for physiological parameters, yield parameters and mineral composition in the leaf tissues.