Molecular Analysis and Production of Multiple-Gene Pyramided Lines for Disease and Insect Resistance in Indica Rice

Biotic stresses such as bacterial leaf blight (BB), Blast and brown planthopper (BPH) are major threats to rice production in South and Southeast Asia. Several single genes conferring resistance to these diseases and insect resistance have lost their resistance due to changes in insect biotypes and disease races in recent years. Thus, there is a need to breed for rice varieties with durable and broad spectrum of resistance to insect pests and diseases. In this study, we transferred three resistance (R) genes, Xa4, xa5 and Xa21 for BB, one (Pi40) for blast and one (Bph18) for BPH from one japonica breeding line, IR 90751-1-14-1-2 into two elite indica varieties (IR72 and NSIC Rc222) genetic background by backcross breeding and marker assisted selection (MAS) using gene-specific, STS and CAPS markers. Initially, F₁ plants with confirmed multiple R genes in heterozygous state were backcrossed with the respective recurrent parents and a set of segregating backcross progenies were developed. Molecular analysis revealed the presence of different gene combinations (2 lines with 5 genes, 12 lines with 4 genes and 10 lines with 3 different genes) in the backcross progenies of two genetic backgrounds. Selected pyramided lines of second backcross progenies were analyzed and some progenies with multiple R genes were identified with 5 R genes. Preliminary bioassays of the five-gene pyramided lines revealed strong resistance to virulent races of BB, Blast and BPH populations of Philippines. Comprehensive incorporation of multiple R genes into elite cultivars will pave the way to improve indica rice production.