Implications of the inoculation method and environment in the selection of melon genotypes resistant to Didymella bryoniae

•Implementing the most appropriate screening condition allows a reliable selection of resistant melon genotypes to D. bryoniae.•Fungal spores’ inoculation must be used for a better differentiation of resistant genotypes.•Although resistance is often assumed as monogenic, it is affected by environmental factors.•The combination of two or more genes does not always generate more resistant individuals than parents. The use of resistant melon cultivars is considered the most effective method to control gummy stem blight, caused by Didymella bryoniae. However, the selection of genotypes is influenced by environmental conditions and the inoculation method. This study aimed to assess how different screening conditions influences resistance classification and the occurrence of environmental effects on melon genotypes with monogenic dominant resistance locus to D. bryoniae. Four experiments with a randomized block design were used to evaluate the reaction of seven melon genotypes, namely the resistant accessions PI 140471, PI 420145, and PI 157082, and their respective crosses. These genotypes were inoculated by mycelial-agar disc or spores and submitted to two environmental conditions (greenhouse or controlled environment). The data from the experiments were initially submitted to an analysis of variance. Subsequently, a joint analysis was performed. The combination of controlled environment with the disc inoculation proved to be more aggressive to all genotypes whereas inoculation via spore was less harmful and allowed a better characterization of the resistance level. Regardless of the inoculation method, differences between genotypes were smaller under greenhouse. Selection of melon genotypes must be caried out considering the occurrence of genotype-environment interactions. Although the conditions provided in the greenhouse reflects the natural environment, the evaluation and identification of resistant genotypes to D. bryoniae should be undertaken in a controlled environment with inoculation by spores.