Fine Mapping a Tarspot Complex Resistance QTL in Maize

Tarspot Complex (TSC), a disease of maize caused by Phyllachora maydis and Monographella maydis, is an increasingly important fungal disease in Latin America. Tarspot Disease, caused by Phyllachora maydis alone, has recently been reported in the USA. Efforts are underway to identify and characterize sources of TSC resistance at CIMMYT. CML495 was identified as a resistance source, and using GWAS the resistance was located on chromosome 8 near the centromere. A biparental DH population was developed by crossing CML495 to a susceptible line, and mapping in this population validated the QTL on chromosome 8. Five TSC resistant DH lines carrying the chromosome 8 donor segment were crossed to 2 susceptible lines to create 10 BC1 populations. BC1 populations were phenotyped to identify which ones were segregating for resistance, and chromosome 8 genotyped to identify donor chromosomal segment map locations. Resistant backcross individuals with donor chromosomal segments across the region containing the QTL were backcrossed to the susceptible recurrent parent to generate additional rounds of recombination, and the QTL location was narrowed to a 2M bp window. BC5 populations will be screened this cycle and linked KASP markers developed for marker assisted breeding.