Mapping QTLs For Heavy Metal Stress Tolerance Using Two Sets Of Reciprocal Introgression Lines In Rice

Study the effects of abiotic stress toxicities, such as Aluminum, ferrous and zinc in crop plants is a dire need of the time. As the time is passing by, the environmental pollutants including soil contaminants are increasing pollution at micro and macro climatic levels. It is doubtless that the industrialization is bringing the general prosperity in society, but there are many evidences that due to industrialization wastes, the lands have been contaminated with heavy metals, such as aluminum, cadmium, copper, chromium, ferrous, zinc e.t.c. Due to these toxicities in agricultural soils not only the area under crop cultivation is decreasing but our food of daily life is also becoming unsafe. Hence keeping in mind the importance of aluminum, ferrous and zinc stress toxicity tolerance at seedling stage in rice, a series of hydroponic experiments for these stress toxicities had been conducted under green house conditions. In addition, these stresses are highly damaging at the seedling stage of rice. Therefore, this study had been conducted at the seedling stage to detect the tolerant QTLs for these stresses in rice. The hydroponic experiments under green house conditions are also time saving, providing more chances for repetition of experiments throughout the year, giving high precision in collection of data and most importantly, we could apply these stresses at commonly required rate of toxicity, which could be the representative rate for field conditions.The main objectives of this study were to analyze the correlation between stress tolerances, to detect the QTLs conferring tolerant to the Al3+, Fe2+and Zn2+toxicities in rice, to validate some major QTLs using derived progenies and to analyze the genetic background effect on QTL expressions of the tested traits, and to confirm the losses caused by aluminum, ferrous and zinc toxicities in rice crop for growth and growth parameters at seedling stage. In this way, this study would be highly beneficial for further development of Al3+, Fe2+and Zn2+toxicity tolerant lines.Rice possesses the greater tolerance against aluminum toxicity stress than many other cereal crops. Hence its tolerance mechanism and genetic factors were brought under genetic study. Most of the farming communities of the developing countries are facing the problem of aluminum toxicity. So for this, a hydroponic experiment for two sets of reciprocal introgression lines derived from the cross of02428/Minghui63injaponica02428background (02428-ILs) and indica Minghui63background (MH63-ILs) were conducted to evaluate aluminum toxicity tolerance (ATT) under the concentration of1.5mmolL-1at the seedling stage in green house. The largest root length was recorded before10days of treatment and after15days of treatment for both control and stress conditions. The ratio of average root elongation under stress versus non stress conditions for each line in each replication was calculated as the relative root elongation (RRE) for evaluation of ATT. The two sets of ILs were genotyped by384evenly distributed SNP markers developed by the two parents. QTLs affecting RRE were mapped by QTL IciMapping software. The parent02428has greater ATT than that of MH63. The RRE of introgression lines for both backgrounds showed dynamic growth and showed tremendous segregations. Fourteen QTLs for all environments, nine QTLs detected in MH63-RILs and five in02428-RILs, were identified on chromosomes1,2,3,4,5,6,8,9,10, and12. Among them, four QTLs (QRl1b, QR12, QRl9and QRL10) on chromosome1,2,9and10were commonly detected in both backgrounds. The preliminary QTL mapping of ATT will provide useful information for further fine-mapping and marker-assisted selection for rice improvement of ATT.Ferrous and Zinc toxicity are two important abiotic stresses which affect the rice production. However, excess Fe2+and Zn2+toxicity can occur in acid soils. Rice plants have a special mechanism to tolerate these two stresses, specially Fe2+and Zn2+stress toxicity tolerant QTLs. Therefore, this research was conducted to find out these QTLs in rice crop for these two abiotic stresses. A hydroponic experiment for two sets of400reciprocal introgression lines derived from the cross of02428/Minghui63in02428japonica background (02428-ILs) and indica Minghui63background (MH63-ILs) was conducted to evaluate Fe2+and Zn2+toxicity tolerance (FZTT) under the concentration of300ppm and200ppm respectively at the seedling stage in green house. The root length (RL), shoot height (SH), root dry weight (RDW) and shoot dry weight (SDW) were recorded after21days of treatment for both control and stress conditions. The ratio of average for these all traits under stress versus non stress conditions for each line in each replication was calculated as the relative traits for evaluation of FZTT. The two sets of ILs were genotyped by265evenly distributed SNP markers developed by the two parents. QTL affecting traits were mapped by QTL IciMapping software. The parent02428has greater FZTT than that of MH63. In total28QTLs for all traits,15QTLs in MH63-ILs and13in02428-ILs were identified. The preliminary QTL mapping of FZTT will be helpful for further development of FZTT lines.Out of these200lines from each background MH63indica and02428japonica, twelve (6%) extreme lines (six highly tolerant (3%) and six (3%) highly susceptible) for ferrous and zinc toxicity tolerant (FZTT) were studied under same environmental conditions to the already finished regular experiments for FZTT. For valid confirmation of extremism in these lines, the experiments were repeated twice with application of ferrous and zinc stresses for21days and26days. The agronomical and physiological effects of these stresses on extreme lines were recorded. The phenotypic performance of tolerant lines from each background MH63indica and02428japonica showed comparatively better toxicity tolerance than sensitive lines during these two different periods of stresses. Therefore, it could be expected that these tolerant lines would be helpful to develop FZTT lines (varieties) to face the challenges of soil contamination problem in future.