Screening And Uptake Mechanisms Of Potassium High Efficiency Genotypes Of Watermelon

The cultivated soil is rich in potassium, but the rate of its direct absorption by plants is very low. With the improvement of crop yield, the potassium content in soil is decreasing. Increasing potassium fertilizer application is a traditional method to ensure high yield of crops. However, In China the resource of potash fertilizer is very poor, large quantities of potash should be needed to import from abroad each year, which is increasing prices of potash and crop production costs. For such a large agricultural country, it is not economical and also can cause environmental pollution. In order to solve this problem, it is important to screen high potassium efficiency genotypes by studying their physiological and genetic mechanisms and by producing new varieties through the means of breeding and molecular biology.In the study, potassium efficient and inefficient genotypes of watermelon were screened by the differences of the K uptake and transition rate between low K and higfi K conditions at the seedling stage. The physiological mechanisms of potassium efficient watermelon genotypes were studied by the analysis of potassium absorption characteristics, which may provide evidence for the improvement of the genetic breeding of crops.1. Screening of Potassium Efficient GenotypesThe results were as follows:33 kinds of genotypes of watermelon were selected in this test, including xiaoxiacheng, xinlan, zhaoyang and so on. Two levels of potassium, low K and high K were selected. The criteria of screening were biomass, K concentration of plant, K uptake, K utilization index, K transport rate and so on. The result showed that K uptake was increased in CK and there were significant differences in K uptake and K utilization indexes among different genotypes of watermelons. Watermelon genotypes were classified into four kinds:Efficient-efficient, inefficient-efficient, efficient-inefficient and inefficient-inefficient genotypes. In small melons, Xiao xiacheng, Zaochun hongyu and Xinlan were efficient-efficient genotypes which showed higher potassium uptake average at both low potassium and high potassium levels. Huang Xiaoyu H, Jintong were inefficient-inefficient genotypes which showed low potassium uptake average at both low potassium and high potassium levels. In medium and large melons, Hei Juba, Teda Tainongbahao and Xin Heilongwang were efficient-efficient genotypes which showed higher potassium uptake average at both low potassium and high potassium levels. Ping 87-14,8424 and Kangbing Dilei were inefficient-inefficient genotypes, which showed low potassium uptake average at both low potassium and high potassium levels.2. Potassium Efficient and Inefficient Physiological and Genetic Mechanisms of Small Melon Potassium GenotypesStudy of potassium absorption kinetics and physiological indicators showed that compared to inefficient-inefficient genotypes, the potassium efficient-efficient genotypes have high root activity, root length and fresh weight. In the potassium uptake kinetics experiments at low potassium, efficient-efficient genotypes showed higher potassium uptake, late absorption equilibrium, potassium maximum absorption rate and potassium affinity than inefficient-inefficient genotypes Huang Xiaoyu H and Jintong. Transporters and channels play an important role in potassium uptake under low potassium conditions. In this experiment, NH4C1 and BaC12 were used as specific uptake inhibitors of transporters and channels, respectively. Under the low potassium condition, when potassium transport protein inhibitors NH4C1 was added, the maximum rate of absorption and potassium affinity of potassium inefficient-inefficient genotypes were significantly reduced by 69% and 61%, but efficient-efficient genotype Zaochun Hongyu was unaffected. This showed that the maximum rate of absorption and potassium affinity of potassium inefficient-inefficient genotypes rely on the ability of transporter protein. Under the low potassium condition, when potassium channel inhibitors BaC12 was added, the maximum rate of absorption of potassium efficient-efficient genotype Zaochun Hongyu was significantly reduced by 28%, but inefficient-inefficient watermelon genotypes Huang Xiaoyu H and Jintong were unaffected. This showed that the maximum rate of absorption of potassium efficient-efficient genotypes rely on the ability of potassium ion channels.3. The Physiological Differences of Medium and Large Melon Potassium Efficient and Inefficient GenotypesStudy of the root characteristics of potassium efficient-efficient and inefficient-inefficient genotypes showed that potassium efficient-efficient genotypes have more dry weight of root, root length, root volume and root surface area. However, there was no difference of the root activity and the average diameter of the root between potassium efficient-efficient and inefficient-inefficient genotypes. Therefore, the reason of the efficient-efficient potassium absorption was higher dry weight of root, root length, root volume and root surface area.