Tolerance of rice germplasm to iron toxicity stress and the relationship between tolerance, Fe2+, P and K content in the leaves and roots

Rice varieties commonly grown in Uganda are generally intolerant to iron toxicity stress. Rice germplasm originating from other countries might potentially have better iron toxicity tolerance. Field and greenhouse experiments were conducted to determine variation in iron toxicity tolerance and uptake of macronutrients in 19 rice cultivars. Iron toxicity reduced grain yield by 34.2% under field conditions and 28.3% under greenhouse conditions. Tolerance to iron toxicity was associated with high biomass production and phosphorus content in the leaves. Resistant cultivars retained more iron in the root tissue, confirming earlier findings that root retention is more efficient as an avoidance/exclusion mechanism. Growth and nutrient uptake showed negative correlation with iron content in the leaves, suggesting that both traits were impacted by iron toxicity. Results showed a significant correlation (r = 0.76) between P and K content of leaves, suggesting that P has a significant role in the uptake of K under iron toxic conditions. Shoot levels of both nutrients seem to determine varietal tolerance to iron toxicity. Four varieties, PNA, K98, IR73678-20-1-B and WITA4, showed less variability in biomass production and nutrient uptake and could potentially serve as new germplasm sources for genetic improvement of rice to iron toxicity.