Field resistance and molecular detection of the orange rust resistance gene linked to G1 marker in Brazilian cultivars of sugarcane

ABSTRACT Sugarcane (Saccharum spp.), an important crop for tropical and subtropical countries, is used in the production of sugar and biofuel. Orange rust, a disease caused by the fungus Puccinia kuehnii, can reduce the yield and harm the sugarcane industry. Molecular markers linked to resistance genes can help breeding programs confirm introgression of favorable alleles, find new resistance sources and release new cultivars that have durable resistance. In the current study, the aims were (i) to evaluate in the field the resistance to orange rust of 24 Brazilian commercial cultivars; (ii) to assess the frequency of the allele at G1 marker locus in the set of cultivars, and (iii) to study the usefulness of G1 marker to predict the resistant phenotype and its potential for marker assisted selection. A diagrammatic scale, which ranged from 1 (plants without symptoms) to 9 (highly susceptible plants), was used to determine the disease severity. Considering resistant cultivars those with mean severity up to 3, G1 marker efficiency in predicting the resistant phenotype was 71.43%. In addition, there was a reduction of 35% in the overall mean severity when G1 marker was present. G1 marker is an important molecular tool that can be used by breeding programs in the search for sugarcane cultivars resistant to orange rust.