Temperature‐Light Intensity Effect on the Antagonism of Species of Cladosporium to Melampsora larici‐populina on Cultivars of Populus X euramericana (Dode) Guinier

The antagonistic and colonistic effect of post‐inoculation temperature and light intensity was investigated in a factorial experiment involving four Cladosporium spp., three poplar cultivars, two levels of temperature and light intensity, anda race of Melampsora larici‐populina. The species of Cladosporium were more antagonistic to uredinial production on the inoculated leaf discs of the cultivars when these were incubated in high temperature – high light intensity than in any other regime. Whilst colonisation of the uredinia was usually minimal in discs incubated on the high temperature – high light intensity regime, the condition of incubation favouring maximum colonisation varied with the cultivar and the species of Cladosporium employed. All the major factors and most of their two‐, three‐ and four‐way interactions were significant determinants of variation in both antagonism to uredinial production and in colonisation of the uredinia produced. The validity ofextrapolation from such experiments to the field environment is discussed.