Research On Potassium Utilization And Yield Formation In Bt Rice

As the most primary cereal crop in world, rice is seriously attacked and threatened by pests. How to make rice avoid pest invasion without traditional chemical pesticides and guarantee or even increase grain yield is worth exploring for high yielding cultivation of rice, which also caused great concerns of breeders in recent years. Bt insect-resistant genes are widely used in transgenic crops for they can effectively kill the lepidoptera pests and do not pollute the environment while also save the cost. But the incorporation of exogenous Bt genes have also produced some changes on non-target characters. Potassium has an important influence on yield formation of rice, then whether potassium nutrition characters of Bt rice would also change is worth researching.Thus, a pot experiment with Og (KO),0.4g (K1) and0.6g (K2) K2O in per kilogram of dry soil was carried out by means of potassium nutrition regulation. Three Bt transgenic rice lines MH63(CrylC*), MH63(Cry2A*), MH63(CrylAb/Ac) and their non-Bt counterpart MH63were used at screenhouse of Huazhong Agricultural University to conduct this test in2012and2013. The study focused on (1) The potassium (K) absorption and utilization characteristics of Bt rice;(2) The photosynthetic production characteristics of Bt rice;(3) The matter translocation and distribution characteristics of Bt rice;(4) The yield and components characteristics of Bt rice;(4) The Bt protein contents in Bt rice lines. These operations aimed to ascertain the effects of exogenous Bt gene on K utilization and distribution and characters of the structure and function of "source-sink-flow" in rice, so the outcomes of the studies could provide references for breeding and establishing a cultivation mode of high production and efficiency of them. The main results are as follows:1. The K distribution and yield formation characteristics of MH63(CrylC*) were different from non-Bt transgenic rice. The total K absorption of above-ground plant parts of MH63(CrylC*) was not lower than that of non-Bt transgenic rice. Compared with MH63, the K accumulation of MH63(CrylC*) in culms and leaves was significantly higher, while that in grains was significantly lower (except K1level in2012). Grain yield of MH63(CrylC*) was significantly lower than that of MH63, which mainly attributed to the remarkably decreased setting rate. The mean grain yield and setting rate of MH63(CrylC*) in two years reduced by27.7%and22.3%than those of MH63, respectively. Compared with MH63, MH63(CrylC*) had higher non-structural carbohydrates (NSC) concentration in culm and sheath at filling and maturing stages, while lower apparent out-transport of NSC in culm and sheath from heading stage to maturing stage, number of small vascular bundles in neck internode at heading and filling stages, diameter and bleeding intensity of neck internode at filling stage. MH63(CrylC*) had higher photosynthetic rate, stomatal conductance, intercellular CO2concentration and transpiration rate at KO level compared with MH63at panicle initiation and filling stages.2. The yield formation characteristics of MH63(CrylAb/Ac) were partly different from non-Bt transgenic rice. MH63(CrylAb/Ac) had lower grain yield than that of MH63(except K1level in2012) which derived from a significantly reduced1000-grain weight; Furthermore, its pollen fertility significantly decreased compared with MH63(in2013). The diameter and bleeding intensity of neck internode at filling stage of MH63(CrylAb/Ac) were significantly lower than those of MH63. There were no significant differences on photosynthetic rate, stomatal conductance, intercellular CO2concentration, transpiration rate and SPAD between MH63(CrylAb/Ac) and MH63.3. There were no significant differences on K distribution and yield formation characteristics between MH63(Cry2A) and MH63. Each measured index of K absorption and utilization characteristics, yield and components characteristics, matter translocation and distribution characteristics, photosynthetic production characteristics for MH63(Cry2A) didn’t have coincidence with those of non-Bt transgenic rice at different potassium levels.4. There were evident correlations between characters of sink and flow. Grain yield and setting rate were highly significantly correlated with apparent out-transport of NSC in culm and sheath, number of small vascular bundles in neck internode; grain yield had significant and greatly significant correlations with diameter and bleeding intensity of neck internode. Apparent out-transport of NSC in culm and sheath was significantly and extremely significantly correlated with number of small vascular bundles and bleeding intensity of neck internode; there were largely significant correlations between diameter and number of small vascular bundles, bleeding intensity of neck internode. Grain yield was quite significantly correlated with setting rate, and aslo had significant correlation with stainable pollen grain rate; there was particularly significant correlation between stainable pollen grain rate and1000-grain weight, too.5. K nutrition had a certain effect on Bt protein expression in Bt rice. Bt protein contents in the three Bt transgenic rice lines at high potassium level (K2) were significantly higher than those at low potassium level (KO) and conventional potassium level (K1). Whether at heading stage or filling stage, the mean Bt protein contents of the three potassium levels were characterized by that MH63(Cry2A*) was the highest, MH63(CrylAb/Ac) followed, and MH63(CrylC*) was the lowest. Bt protein contents at filling stage of MH63(CrylC*) and MH63(Cry2A*) were higher than those at heading stage, while that of MH63(CrylAb/Ac) was inverse.6. Bt transgenic and non-Bt transgenic rice lines (MH63) had no sensitive reaction to potash application treatments. Most measured indexes of K absorption and utilization characteristics, yield and components characteristics, matter translocation and distribution characteristics, photosynthetic production characteristics of all the rice lines did not increase with the improvement of potash.Some changes have taken place in K utilization and "source-sink-flow" characteristics of MH63by the incorporation of exogenous Bt genes, which we could take corresponding improved breeding technology and high yield cultivation measures to insure and improve K utilization and yield formation potential of Bt rice according to different characteristics of different Bt rice lines in breeding and cultivation practices.