Development of dominant rice blast Pi-ta resistance gene markers

Incorporation of resistance genes into existing rice (Oryza sativa L.) cultivars is a powerful strategy and is commonly applied in breeding rice resistance to blast disease [caused by Pyricularia grisea Sacc. = P. oryzae Cavara (teleomorph: Magnaporthe grisea (Hebert) Barr)]. The rice blast resistance gene, Pi-ta, originally introgressed into japonica from indica rice is important in breeding for rice blast resistance worldwide. In the southern USA, the rice cultivar Katy contains Pita and is resistant to the predominant blast M. grisea races IB-49 and IC-17 and has been used as the blast resistant breeding parent. Three pairs of DNA primers specific to the dominant indica Pi-ta gene were designed to amplify the Pi-ta DNA fragments by polymerase chain reaction (PCR). PCR products amplified by these Pi-ta specific primers were cloned and sequenced. Sequence analysis confirmed the presence of the dominant indica Pi-ta allele. These Pi-ta primers were used to examine the presence of Pi-ta alleles in advanced Arkansas rice breeding lines. The Pi-ta containing rice lines, as determined by PCR analysis, were resistant to both IB-49 and IC-17 in standard pathogenicity assays. In contrast, lines lacking the Pi-ta genes failed to protect rice plants against both races IB-49 and IC-17. The presence of Pi-ta markers correlated with the Pi-ta resistance spectrum. Thus, the Pi-ta gene markers provide a basis for stacking other blast resistance genes into high yielding and good quality advanced breeding rice lines.