Introgression of anthracnose resistance loci into a sweet sorghum genetic background

Abstract

Sweet sorghum is becoming an important source of feedstock to produce renewable fuels that can be highly affected by anthracnose (Colletotrichum sublineola), a major disease affecting all aboveground parts of the plant. The high genetic diversity of the pathogen requires multiple resistance genes to achieve stable resistance over environments. Herein, three anthracnose resistance loci on chromosome 5 (Sobic.05G172300, Sobic.05G182400, and Sobic.05G228400) and one locus on chromosome 9 (Sobic.09G13300) identified in grain sorghum were introgressed into the susceptible sweet cultivar ‘Early Honey’ (EH) to determine their effectiveness across genetic background. Eight grain sorghum lines (SC15, SC110, SC1033, SC1330, SC17, SC1321, SC155, and SC13) with different combinations of these resistance loci were chosen as sources of anthracnose resistance. Marker-assisted backcrossing using four high-throughput single nucleotide polymorphism (SNP) markers tagging these loci were used to develop 42 BC3F4 lines with different resistance loci combinations. The anthracnose response of these lines and the parental lines were evaluated in Georgia, Texas and Puerto Rico in 2023. Twelve BC3F4 lines derived from SC15, SC110 and SC1321 displayed resistance across locations and two showed variable response. Evaluation of these lines in Georgia, Texas and Puerto Rico in 2024 confirmed the resistance response across locations of eleven BC3F4 lines. These new lines enclose resistant alleles for one or both loci of Sobic.05G172300 and Sobic.05G182400. Therefore, some anthracnose resistant loci from grain sorghum remain functional in the sweet sorghum genetic background. These lines represent a new source of broad resistance to anthracnose for the improvement of sweet sorghum germplasm.