IRC2014_MS11
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This study conducted early-generation field screening followed by marker-assisted backcrossing to introduce disease resistance genes into the temperate japonica rice variety MS11. Screening of backcross progenies with isolates specific to the targeted resistance genes showed high correspondence between genotype and phenotype, suggesting molecular markers can be useful in selecting lines with the desired resistance in the MS11 background. The results indicate disease resistance from different donors is well expressed in MS11, and molecular markers can guide further backcrossing to develop temperate rice varieties with improved resistance to bacterial blight and blast.
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IRC2014_MS11
- 1. Temperate rice in the tropics: upgrading MS11 disease resistance through early-generation morphological field screening and marker-assisted backcrossing We conducted an early-generation morphological selection in IRRI fields followed by marker-assisted backcrossing, increasing the possibility of detecting successful breeding lines with useful disease resistance (R) genes for further evaluation. Screening with isolates specific to the target R genes revealed a high correspondence between genotype and phenotype, suggesting the usefulness of molecular foreground markers in the MS11 background. Ian Paul Navea, Woon-Chul Shin, Jonas Padilla, Ruby Burgos, Gideon Torollo, Katreena Titong, Chenie Zamora, Bo Zhou, Isabelita Oña, Casiana Vera Cruz, Ki- Young Kim, Bo-Kyeong Kim, Woon-Goo Ha, Woon-Sang Yeo, and Joong Hyoun Chin International Rice Research Institute, DAPO Box 7777, Metro Manila 1301, Philippines Email address: i.navea@irri.org Materials and methods Plant materials Acknowledgments This study was supported by RDA-IRRI collaboration projects funded by the Rural Development Administration, Republic of Korea. Special thanks go to Brian Montes and Crisipulo Cura for the technical support. P630 Recurrent parent (RP): MS11 (a high-quality japonica, Jinmibyeo/Cheolwon 46, 20% yield gain in the Philippines) Resistance donors (DP): Bacterial blight: IRBB66 (Xa4+xa5+Xa7+xa13+Xa21)—Xa4 and Xa7 are the main priorities because of temperature stability of resistance Blast: IRBL9-W (Pi9 – broad-spectrum) Early-generation field selection BC1F2 segregating generation was grown in the field without genotyping. Plants were selectively harvested with the following criteria: Good fertility MS11-like plant shape Foreground genotyping Bulk segregant analysis (BSA) was done for the selected lines of BC1F2. Panicles from plants selected from the BSA were propagated in the field. Table 1. List of makers used for foreground genotyping. Marker Target R gene Donor Pi9-1 Pi9/Pi2 WHD-1S-75-1-127 Pi9-2 Pi9/Pi2 WHD-1S-75-1-127 MP Xa4 TKM 6 xa5-R xa5-resistant Aus Boro lines xa5-S xa5-susceptible M5 Xa7 DV85 xa13-130-147 xa13 BJ1 (Aus Boro) Xa21 Xa21 O. longistaminata Screening using artificial inoculation BC1F3 plants were grown in screenhouses and screened for isolates differential to the target R genes. Fig. 1. Blast artificial inoculation setup. Fourteen days after sowing (DAS), seedlings were misted with blast fungal spore suspension differential to Pi9. Monogenic line screening with different isolates revealed that Ca41 discriminates the Pi9 gene from other blast-resistance genes (data not shown). Fig. 2. Artificial inoculation of PXO61 (AvrXa4) and PXO86 (AvrXa7) by clipping method 45 DAS. Results and discussion There was a high correspondence between marker scores and screening results. (Pi9) Line Ca41 scorea Pi9-1 Pi9-2 RP 5 absent absent DP 0 present present MSPi-24 1 present present MSPi-28 0 present present MSPi-34 0 present present MSPi-44 2 present present MSPi-47 0 present present MSPi-50 0 present present MSPi-55 1 present present MSPi-57 0 present present MSPi-61 2 present present MSPi-63 0 present present Table 2. Blast scores of RP, DP, and backcross progenies together with marker scores. Fig. 3. Ca41 isolate reactions of RP, DP, and improved backcross progenies. Photos were taken 14 days post-inoculation. (Xa4 + Xa7 + more R genes) Line Lesion length (cm) R genesa Xa4 xa5 Xa7 xa13 Xa21 RP 81.52 ± 2.26 S S S S S DP 15.98 ± 2.36 R R R R R MSBB-102 2.06 ± 0.33 R R R H H MSBB-188 2.43 ± 0.39 R R S H S MSBB-042 2.72 ± 0.82 R R S S H MSBB-166 2.78 ± 0.73 R R S S S Table 3. Lesion length and marker scores of the RP, DP, and 4 lines selected for additional backcrossing. a0 = completely resistant, 5 = completely susceptible. aR, S, and H are resistant, susceptible, and heterozygous, respectively. Fig. 4. Reactions of leaves inoculated with isolates differential to Xa4 and Xa7, PXO61 and PXO86, respectively. Fig. 5. Segregation of backcross progenies at the R-gene loci. Disease resistance conferred by the R genes from different donors is highly expressed in the MS11 background, a temperate japonica. With high correspondence to the screening results, the molecular markers used in this study can be used for additional backcrossing of selected progenies. In the advanced backcross generation, high-throughput background genotyping will be applied together with field inoculation of bacterial blight and blast isolates. Conclusions