Time-Varying BTFs

lron toxicity is a widespread nutritional disorder of rice in wetlands characterized by large concentrations of reduced iron (Fe) in the soil solution. It is associated with poor water control, resulting in reducing soil conditions that promote the accumulation of soluble ferrous iron in the soi! solution. Genetic improvement is considered the most promising strategy to counteract negative effects of iron toxicity on rice. Within the genus Oryza, only accessions of the species Oryza sativa and O. glaberrima have so far been assessed for their tolerance to elevated concentrations of iron in solution. However, the genus Oryza comprises 23 species that may contain genes of interest and represent a so far completely untapped potential for future rice breeding research. We hypothesize that rice wild relatives might have evolved adaptive mechanisms to abiotic stresses including iron toxicity, thus enlarging the gene pool for future rice breeding work for iron stress tolerance. The present research aimed at characterizing selected domesticated O. sativa and 0 glaberrima as weil as 62 accessions belonging to the other species of Oryza (wild relatives) at the vegetative growth stage for their response to elevated Fe(lI) in soi! solution. A total of 75 genotypes belonging to 21 different species of Oryza were comparatively assessed in a greenhouse experiment. Twelve-day-old seedling were transplanted into polders that were enriched with reduced iron either to represent a constant moderate iron concentration in the soil (chronic stress) or a short-term high iron pulse (acute stress). Toxicity symptoms were assessed as Leaf Bronzing Scores (LBS) on ascale from 0 to 10. Genotypes responded differently to the two types of Fe stress. Early formation of LBS and subsequent recovery was observed with acute Fe stress while more constant but also less severe symptoms occurred with chronic stress. Genotypes belonging to the species O. nivara showed the lowest LBS under acute stress, while O. sativa genotype FL483 expressed the lowest LBS under chronic Fe stress. Based on the relationship of leaf iron concentration and LBS some accessions of the species O. rufipogon and O. nivara could be classified as tolerant includer types (tolerating high tissue concentrations of iron), whi!e other accessions of O. nivara and most accessions of O. barthii could be classified as excluder types (limiting the uptake of iron by the roots). Based on this preliminary assessment we conclude that some wild relatives of rice have potential and may be of interest for future rice breeding strategies for tolerance to conditions of iron toxicity.