Molecular Markers Associated with Phosphorus Uptake and Internal Phosphorus-Use Efficiency in Rice

Abstract

Phosphorus (P) deficiency is a major constraint to rice production. Increasing the P-deficiency tolerance of rice cultivars may represent a more cost-effective solution than relying on fertilizer application. The objective of this study was to identify putative QTLs for P-deficiency tolerance in rice, using 98 backcross inbred lines derived from a japonica * indica cross. Lines were genotyped at 245 RFLP marker loci and grown on P-deficient soil to evaluate their P uptake and internal P-use efficiency. Four QTLs were identified for P uptake, explaining 54.5% of the variation for this trait. One QTL linked to marker C443 on chromosome 12 had a major effect, accounting for about half of the explained variation. Two of the three QTLs detected for internal P-use efficiency, including the major one on chromosome 12, coincided with QTLs for P uptake as well, however, whereas indica alleles increased P uptake they reduced P-use efficiency. We concluded that this was not due to tight linkage of two genes in repulsion but rather due to an indirect effect of P uptake on P-use efficiency because most lines with high P-use efficiency were characterized by very low P uptake and low dry weight and apparently experienced extreme P-deficiency stress. In this study P-deficiency tolerance was thus mainly caused by genotypic differences in P uptake and genotypic differences in P-use efficiency and dry matter production were merely reflections of differences in P uptake. Lines with indica alleles at the major QTL on chromosome twelve had twice the P uptake compared to lines with japonica alleles. After further confirmation and fine mapping, this major QTL should be a prime target for isolating the gene or genes increasing P uptake in rice.