Introgression of , and for resistance to bacterial blight in thermosensitive genetic male sterile rice ( L.) for the development of two-line hybrids

Bacterial blight (BB) of rice caused by pv. is a major production constraint in commercial hybrid rice production in the Philippines because most of the parental lines used in hybrid production do not carry resistance genes against the pathogen. In this study, three bacterial blight resistance genes, , and , were introgressed to a temperature-sensitive genetic male sterile (TGMS1) line. A three-way cross of AR32-19-3-3/TGMS1//IRBB4/7 (PR36944) was made to produce 1,364 F plants carrying various combinations of , and . Individual plants were characterized for reaction to bacterial blight PXO61 (race 1), PXO86 (race 2), PXO99 (race 6) and pollen sterility. Of 144 F plants demonstrating resistance against PXO61, PXO86 and PXO99, 22 exhibited highly resistant phenotypes with mean lesion lengths ranging from 0.37–2.97 cm. Analysis of disease reaction identified 20 potential TGMS F plants containing , and while 78 plants with +. Phenotypic and polymerase chain reaction (PCR) analyses confirmed PR36944-450, PR36944-473 and PR36944-700 as homozygous for and and highly resistant to all three races. Fertility of PR36944-450 and PR36944-700 was restored at permissive temperature in a growth chamber. BB-resistant TGMS lines should facilitate breeding two-line hybrids in the tropics.