The effect of inoculation temperature on the reaction of potato cultivars to Synchytrium endobioticum

The reactions of potato cultivars to inoculation with germinating winter spores of Synchytriuum endobioticum at 10, 15 and 20°C were compared. The classification of wart reactions for cultivars at the Resistant Grade 1/Resistant Grade 2 (RG1/RG2) and RG2/susceptible borderlines was found to depend on the inoculation temperature. For RG2 cultivars, there was a clear increase in the proportion of more resistant reactions with increase in inoculation temperature. The borderline cultivars 'Teena' and 'Alhamra' reacted as RG2 when inoculated at 10°C and as RG1 when inoculated at higher temperatures. However the inoculation temperature is unlikely to influence the outcome of tests on cultivars that produce a higher percentage of RG2 reactions. An inoculation temperature of 10–15°C more readily identified cultivars that are slightly susceptible. The slightly susceptible cultivars 'Apache', 'Morven' and 'Hassia' reacted as susceptible at 10 and 15°C and as RG2 at 20°C. However, cultivars known to produce wart tissue, including the very slightly susceptible 'Altena', were found readily to produce susceptible reactions when inoculated at all the temperatures tested.