Marker-Assisted Simultaneous and Stepwise Pyramiding of Broad-Spectrum Bacterial Leaf Blight Resistance Genes, Xa33 and Xa38, into Salt-Tolerant Rice Variety “CO43”

Bacterial leaf blight (BLB) disease is one of the most important diseases of rice in India and worldwide. The management of this disease becomes extremely challenging due to the presence of Xoo races with varying level of virulence and diversity. The development of BLB-resistant rice lines with the help of marker-assisted selection has been proven as one of the most effective strategies to sustain rice cultivation. This study demonstrates marker-assisted introgression and pyramiding of two broad-spectrum BLB genes (Xa33 and Xa38) into the background of “CO43,” a popular fine white-grained rice cultivar, tolerant to saline coastal areas in southern India. Two separate marker-assisted backcrossing schemes were used, and at each stage of backcrossing, foreground, recombinant, and background selection were carried out. Backcross-derived lines possessing either Xa33 or Xa38 along with maximum genome recovery of “CO43” were identified at BC₂F₁ generation, intercrossed with each other to pyramid the genes, and selfed to identify homozygous lines for the pyramided genes. The performance of the improved “CO43” lines, such as lines # 2_7_78, 2_7_102, 6_9_65, and 6–8-76 exhibited enhanced broad-spectrum resistance to BLB (lesion length, LL 0.0 ± 0.0 to 0.9 ± 0.1 cm). Furthermore, the improved “CO43” lines maintained the agro-morphological features of the recurrent parent along with enhanced BLB resistance. These lines with effective and durable resistance would contribute to sustainable rice production in coastal areas of southern India.