Validation of the G1 Molecular Marker Associated with Resistance to Orange Rust in Brazilian Sugarcane Genotypes

Abstract

Orange rust, caused by the fungus Puccinia kuehnii, is an important disease of sugarcane (Saccharum sp.). A molecular marker (G1) was developed to identify the resistance of sugarcane to orange rust. The aim of the present study was to validate the molecular marker G1 in the detection of resistance to orange rust in Brazilian sugarcane genotypes. 80 genotypes were analyzed by PCR, being classified according to the presence or absence of the marker. For field evaluation of orange rust resistance, a randomized block experiment was conducted, with the same 80 genotypes using four replications. Artificial inoculation was performed in the leaf whorl, with an evaluation made at 30 days after inoculation, using a scale from zero (without symptoms) to four (more than five pustules with sporulation), in which cultivars with an average score between zero and two were classified as resistant, and a score greater than two, susceptible. Of the 17 genotypes classified as resistant through the field test, 9 did not present the respective band. Of the 63 susceptible genotypes, 27 had the band relative to the molecular marker G1. The selection accuracy of G1 marker (the efficiency of predicting resistant phenotype) was 22.86%. The Phi correlation coefficient (ϕ) was calculated, through which it was observed that the variables are independent, with no statistically significant correlation between them. The results indicate that the G1 marker had a low efficiency to predict the resistance to orange rust in clones under selection in a Brazilian breeding program and Brazilian commercial cultivars of sugarcane.