Early selection of garden rose seedlings for powdery mildew resistance

A selection protocol to screen for powdery mildew resistance at an early stage in rose progenies was evaluated. Seedlings were grown in the first year in two separate greenhouse compartments: one with inoculation plants (C1) and one without (C2; control compartment). In the second year, the same genotypes were tested in the field under natural infection conditions. In the compartment with inoculation plants a high and uniform infection pressure was established. Selection for disease resistance could start more than one month earlier in the greenhouse compartment with inoculation plants compared to the control compartment. Significant correlations between greenhouse evaluation and field scores were found, especially for the families (F-1) of different crosses. In commercial breeding, the proposed method can significantly reduce selection efforts and allows for a more economical and efficient manner to screen on a larger number of seedlings for resistance