Although blast R gene Pi41 was previously reported in cv. 93-11 [47], additional R genes must also be present [26], [31], [49], [50], [51], [52] and [53]. The objectives of the present

study were to evaluate blast resistance in cv. 93-11 using a wide range of Chinese M. oryzae isolates, and to identify and map R genes additional to Pi41. Five rice cultivars, one near-isogenic line (NIL) and ten monogenic lines (MLs) were used in this study (Table 1). Indica cv. 93-11 (resistant, male parent) and japonica cv. Lijiangxintuanheigu (LTH, susceptible, female parent) were evaluated for reaction to M. oryzae isolates, and crossed to develop F2 and F3 populations for genetic analysis and gene mapping. Cultivars CO39, Aichi Asahi and IR64 together with 11 NILs/MLs, each carrying a single R gene ( Table 1), were used as reference lines to differentiate the genes mapped in 93-11 from learn more previously reported R genes. 93-11, LTH, Aichi Asahi, IR64 and F-128-1

are maintained at the Institute of Crop Science, Chinese Academy of Agricultural MK-2206 nmr Sciences (CAAS), Beijing, China. CO39 and the other 10 MLs were kindly provided by Dr. Yoshimichi Fukuta, International Rice Research Institute (IRRI), Los Baños, The Philippines. Seedlings were grown in 60 cm × 30 cm × 5 cm plastic seedling trays in a greenhouse. Pre-soaked seeds of test materials were sown in rows together with the parents. For genetic analysis and gene mapping, 300 seeds of the F2 population and 15 seeds of each parent were sown per tray. For differentiating R genes, 15 seeds of each of the two parents and 11 reference lines ( Table 1) were sown in each tray with two replications. A total of 495 M. oryzae isolates from different rice growing regions were used to evaluate the reaction of cv. 93-11. Among them, five isolates — three

indica-derived isolates, 001-99-1 (pathotype 241.6, from Jiangsu of China), RB17 (pathotype 423.2, from Hunan of China), and GZ26 (pathotype 541.0, from Guizhou of China), and two japonica-derived isolates, 99-26-2 Succinyl-CoA (pathotype 437.1, from Beijing of China) and P-2b (pathotype 303.0, from Japan) — provided clear resistant or susceptible reactions on the two parents and 11 reference lines ( Table 1) and were chosen for further studies. All isolates are stored at the Institute of Crop Science, CAAS, Beijing, China. Inoculum preparation and seedling inoculation followed the procedure described by Chen et al. [60]. Disease reactions were evaluated 6–7 days after inoculation on a numerical scale ranging from 0–3 (resistant) to 4–5 (susceptible) as described by Mackill and Bonman [4]. Observed reactions were verified in the field following injection-inoculation as described by Lei et al. [61]. Genomic DNA was extracted from seedling leaves using the CTAB method [62]. Two sets of DNA bulks, each containing a resistant pool and a susceptible pool, were prepared following the methods described by Yang et al. [47].