Genotypic differences and some associated plant traits in potassium internal use efficiency of lowland rice (Oryza sativa L.)

As potassium (K) deficiency in paddy soils is becoming one of the limiting factors for increasing rice yield in Asia, it is important to identify genotypic differences and exploit genetic potential for K use efficiency in lowland rice. Successful identification of K-efficient genotypes and genetic improvement largely depend on development of accurate and feasible screening parameters and methods. In this study, over 134 rice (Oryza sativa L.) genotypes were tested under nutrient solution and field conditions at low and adequate K levels to examine genotypic differences in K internal use efficiency (KIUE) and identify the associated plant traits. Marked differences in K internal use efficiency for biomass production (KIUE-B) and for grain production (KIUE-G) were observed among the rice genotypes. The KIUE-B at the seedling stage (g DWg(-1) K taken up) differed sixfold among the 134 rice genotypes under low K. A positive and close correlation was observed between the relative shoot and root dry matter yields, relative root K accumulation and the KIUE-B at the seedling stage, respectively. However, a negative and significant correlation was found between the KIUE-B and the relative K concentrations in shoots and roots, and the relative K accumulation in shoots, respectively. The results from the two years of field experiments showed that rice genotypes with greater KIUE-B at the seedling stage had higher KIUE-B at the tillering stage and higher KIUE-G at physiological maturity. Both KIUE-B at the tillering stage and KIUE-G at physiological maturity were closely and positively correlated with the relative shoot dry matter yield in shoots at the tillering stage and harvest index under low K, and had a highly significant and negative correlation with the shoot K concentration and accumulation at low K among the nine rice genotypes. Therefore, the K internal use efficiency could be used as an index for selecting K-efficient genotypes. The relative shoot biomass, relative root length, K concentration and accumulation in shoots as well as harvest index are among the most important plant traits for identifying K-efficient genotypes in lowland rice.