Assessment of the Effect of Temperature on the Late Blight Disease Cycle Using a Detached Leaf Assay

Abstract

Phytophthora infestans is a fungal-like organism belonging to the Phylum Oomycota, which is currently classified within the Kingdom Stramenopila. This oomycete is the causal agent of potato late blight, and as such, it is believed to be a major contributor to the Potato Famine, which ravaged Ireland in the 1840's. Current annual losses worldwide due to P. infestans gross over $6.8 billion. Interactions between two different isolates of the US-8 race and three potato (Solanum tuberosum) cultivars, and in particular, the effect of temperature on the disease cycle, were analyzed using a Detached Leaf Assay (DLA), under controlled laboratory conditions. Incubation period was variable between conditions and, in general, incubation period was longest for each isolate at low temperatures. For isolate NC092ba, mean incubation period was longest at 12°C and did not vary significantly between cultivars. At 18°C, incubation period also did not vary between cultivars but it was shorter than at 12°C. For leaves infected at 24°C with isolate NC092ba, there was a significant difference in incubation period between cultivars, with Russet Burbank being longest. For leaves infected with isolate PSUPotb, incubation period was again longest at 12°C and there was no significant difference between cultivars. At 18°C and 24°C, incubation period was longer for Russet Burbank than for Kennebec or Red Norland. Furthermore, disease progress over time was more severe at higher temperatures for each isolate, across cultivars. Confirmation of pathogen presence in infected leaf tissue was successfully obtained using previously developed P. infestans specific primers in a standard Polymerase Chain Reaction (PCR) assay.