Molecular Marker-Assisted Selection for o2 Introgression Lines with o16 Gene in Corn

Mutant opaque-2 (o2) is commonly used as a donor in high lysine corn (Zea mays L.). Currently, the highest lysine content of the o2 line or the resultant hybrid is only 0.4%, and it is necessary to breed corn lines with higher lysine content. This study aimed at transferring another high lysine gene, opaque-16 (o16), into o2 corn line. The o16 donor parent QCL3021 was crossed and backcrossed with Taixi 19 (o2 line) until the BC2F4 generation. In every backcrossing and subsequent inbred generation, o2 and o16 genes were selected using simple sequence repeat (SSR) markers umc1066 and umc1141, respectively. The backgrounds of selected plants were screened with 243 SSR markers spanning over the whole corn genome. Grain lysine content was determined using the dye-binding lysine (DBL) method. In the BC2F4 generation, 17 lines carrying both o2 and o16 were harvested, of which the genetic background recovery ratios were as high as 92-95%. This indicated that the genome of these lines was highly identical with the o2 line. Lysine contents of the selected plants ranged from 0.47% to 0.60%. The average lysine content of these plants was 125% higher than that of normal corn, 23% higher than the high parent Taixi 19, and 64% higher than the low parent QCL3021.