Phytophthora cinnamomi exhibits phenotypic plasticity in response to cold temperatures

Abstract

Phytophthora cinnamomi has recently been found in highly diverse and fragile alpine and sub-alpine environments previously considered P. cinnamomi and disease free due to low temperatures. In the laboratory, we investigated the ability of P. cinnamomi isolates to adapt to cold and cause disease under conditions comparable to alpine and sub-alpine environments. Initially, the ability of P. cinnamomi isolates to produce sporangia at 10 °C (2 °C lower than previously reported in the literature) was demonstrated in vitro. The lowest temperature limit for host infection was determined (i.e., 8 °C) and the phenotypic plasticity of isolates was then explored in planta in two successive phenotypic plasticity experiments comparing cold 9, 7.5 °C, and ambient temperature 25 (±5 °C). In the phenotypic plasticity experiment-1, three of the five isolates recovered from plants grown at 9 °C produced sporangia and released zoospores (infective propagules) at 7.5 °C, even lower than determined initially, i.e., 10 °C. No changes were observed in the same set of isolates recovered from plants grown at ambient temperature in the glasshouse as a control, which shows that P. cinnamomi can exhibit phenotypic plasticity and responds rapidly to selection pressure and adapts to new environments. Although P. cinnamomi isolates could produce infective propagules at 7.5 °C in vitro, they could not be recovered from inoculated plants grown at 7.5 °C after 3 months in phenotypic plasticity experiment-2. More work is, therefore, needed to establish disease development by P. cinnamomi at 7.5 °C and below.