Nature of resistance of seven melon lines to Sphaerotheca fuliginea

The nature of resistance of Sphaerotheca fuliginea Poll. race 1 was investigated in leaves of susceptible, moderately resistant and resistant genotypes of Cucumis melo . For this purpose three different tests were carried out. The first one was designed to assess whether resistance was caused by pre- or post-infectional mechanisms, and the other two tests were focused to determine if any differences were present in the progression ratio of the disease, measured as the delaying time in conidiophore and conidia formation, among the different cultivars which were tested. The results showed that in the resistant controls ('PMR5' and 'PI 124111'), the resistant reaction was probably due to pre-infectional mechanisms, or at least very near to the moment of infection, while in the moderately resistant and resistant Spanish local cultivars it was clearly due to post-infectional mechanisms characterized by an important delay in the growth and development of the fungus when compared with the susceptible cultivars. Suggestions are made for the development of more successful breeding programmes.