Conventional Breeding and Molecular Markers for Blast Disease Resistance in Rice (Oryza sativa L.)

Monogenic lines, which carried 23 genes for blast resistance were tested and used donors to transfer resistance genesby crossing method. The results under blast nursery revealed that 9 genes from 23 genes were susceptible to highlysusceptible under the three locations (Sakha, Gemmeza, and Zarzoura in Egypt); Pia, Pik, Pik-p, Piz-t, Pita, Pi b, Pi,Pi 19 and Pi 20. While, the genes Pii, Pik-s, Pik-h, Pi z, Piz-5, Pi sh, Pi 3, Pi 1, Pi 5, Pi 7, Pi 9, Pi 12, Pikm and Pita-2were highly resistant at the same locations. Clustering analysis confirmed the results, which divided into two groups;the first one included all the susceptible genes, while the second one included the resistance genes. In the greenhousetest, the reaction pattern of five races produced 100% resistance under artificial inoculation with eight genes showingcomplete resistance to all isolates. The completely resistant genes: Pii, Pik-s, Piz, Piz-5 (=bi2) (t), Pita (=Pi4) (t), Pita,Pi b and Pi1 as well as clustering analysis confirmed the results. In the F₁ crosses, the results showed all the 25 crosseswere resistant for leaf blast disease under field conditions. While, the results in F₂ population showed seven crosseswith segregation ratio of 15 (R):1 (S), two cross gave segregated ratio of 3 R:1 S and one gave 13:3. For the identi-fication of blast resistance genes in the parental lines, the marker K3959, linked to Pik-s gene and the varietyIRBLKS-F5 carry this gene, which was from the monogenic line. The results showed that four genotypes; Sakha105, Sakha 103, Sakha 106 and IRBLKS-F5 were carrying Pik-s gene, while was absent in the Sakha 101, Sakha104, IRBL5-M, IRBL9-W, IRBLTACP1 and IRBL9-W(R) genotypes. As for Pi 5 gene, the results showed that itwas present in Sakha 103 and Sakha 104 varieties and absent in the rest of the genotypes. In addition, Pita-Pita-2 gene was found in the three Egyptian genotypes (Sakha 105, Sakha 101 and Sakha 104) plus IRBLTACP1 monogenetic. In F2 generation, six populations were used to study the inheritance of blast resistance and specific primersto confirm the ratio and identify the resistance genes. However, the ratios in molecular markers were the same of theratio under field evaluation in the most population studies. These findings would facilitate in breeding programs forgene pyramiding and gene accumulation to produce durable resistance for blast using those genotypes.