Influence of low temperature and frost duration on Phytophthora alni subsp. alni viability

Abstract

Limits on the survival of P. alni subsp. alni (PAA) due to low temperature can be expected based on previously published laboratory and field studies. This study presents a laboratory experiment to test the influence of low temperature and frost duration on PAA viability. Ten PAA isolates were incubated at different temperatures (–0.1, –2.5, –5.0, –7.5, and –10.0 °C) and frost durations (0 – 7, 14, 21, and 28 days). A regression analysis confirmed the significant influence of both factors (low temperature and frost duration, and their interaction) on the survival of the pathogen under laboratory conditions. The survival and failure time analysis showed that the survival of the pathogen differs significantly after mild frost (all the isolates tested survived temperatures between –0.1 and –5.0 °C during the entire testing period) and heavy frost (the pathogen died after 21 days of incubation at –7.5 °C and after 2 days at –10.0 °C). Moreover, the viability of the pathogen decreased significantly if the temperature of –5.0 °C was maintained for at least 1 week and the temperature of –7.5 °C persisted in laboratory conditions for at least 4 days. The results of the study proved the pathogen to be very sensitive to heavy frost. The low-temperature limits for PAA occur regularly in Central Europe in January. It is probable that these temperatures can reduce PAA populations in diseased black alder stems. The climate change characterised by increases in the lowest minimum winter temperatures in Central Europe (as hypothesised by IPCC) may pose a significant risk for affected alder population in the area.