DNA Markers Associated with Blue Disease and Bacterial Blight Resistance Genes and Their Applications in Cotton Breeding

Resistance to cotton blue disease (CBD) and bacterial blight (BB, race 18) was evaluated respectively in F_2.3 and F_2.5 populations derived from a cross between resistant variety ‘Delta Opal’ and susceptible variety ‘DP388’. The CBD and BB resistance in ‘Delta Opal’ was controlled by one single dominant gene designated Cbd and B_12, respectively. For the blue disease resistance gene Cbd, two simple sequence repeat (SSR) markers were identified as linked to Cbd at the telomere region of chromosome 10 (A10). SSR marker DC20027 was 0.75 cM away from Cbd. DC20027 marker fragments amplified from 3 diploid species and 13 cotton varieties whose CBD resistance was known were cloned and sequenced. One single nucleotide polymorphism (SNP) was identified at the 136^th position by sequence alignment analysis. For the bacterial blight resistance gene B₁₂, three SSR markers, CIR246, BNL3545 and BNL3644 on the telomeric region of chromosome 14 (D02), were found closely linked to B₁₂. The association between marker CIR246 and B₁₂ was validated among 354 plants of 16 diverse varieties. These markers enabled marker assisted selection for high levels of CBD and BB resistance in cotton breeding programs.