Breeding for Phosphorus Deficiency Tolerance

Insufficient amounts of phosphorus (P) in soils with P-fixing properties result in reduced tilllering, delay in flowering, and yield losses, making P an essential inorganic plant nutrient in agriculture. It is therefore important to develop P-efficient crops. The identification of the Phosphorus Uptake 1 (Pup1) QTL from tolerance donor Kasalath was the first significant step toward the development of P-efficient rice varieties. Gene-specific molecular markers spanning the Pup1 genomic region were then developed to facilitate molecular breeding of such varieties. The Pup1 locus has been introgressed into IR64, IR74, and in Indonesian varieties Batur, Situ Bagendit, and Dodokan. Phenotypic data showed higher grain yield per plant in IR74-Pup1 lines in pot as well as field experiments. Similar data were obtained in field experiments using Pup1 introgression lines of Indonesian upland varieties Batur and Situ Bagendit. A beneficial effect from Situ Bagendit and Batur introgression was observed in low-P-application fields in Indonesia. Some selected Situ Bagendit- and Batur-Pup1 NILs are being tested under P-deficient conditions. The transgenic approach was also conducted to further analyze the function of Pup1. Sequencing of the Pup1 locus now reveals the presence of a novel Ser/Thr protein kinase gene, PHOSPHORUS STARVATION TOLERANCE 1 (OsPSTOL1). This gene is located in a Kasalath-specific insertion-deletion (~90 kbp) region and confers tolerance by enhancing root growth. The enhanced root growth provides plants with an advantage in  accessing P and other soil nutrients.