Higher Temperature and Host Age Alter Infection Outcomes in a Multi-Pathogen System

Area of Science:

• Plant pathology
• Ecology
• Climate change research

Background:

• Pathogen infection outcomes are influenced by environmental factors like temperature, pathogen interactions, and host age.
• Few studies have experimentally investigated the combined effects of warming, multiple pathogen species, and host age on infection.
• Understanding these interactions is crucial for predicting disease dynamics under climate change.

Purpose of the Study:

• To experimentally test how plant age and temperature affect infection outcomes of two distinct foliar fungal pathogens in tall fescue.
• To assess the influence of coinfection by pathogens with contrasting feeding strategies (necrotroph and hemibiotroph) under varying conditions.
• To determine the relative importance of host age, temperature, and pathogen interactions on disease severity.

Main Methods:

• A factorial experiment was conducted using tall fescue plants at two ages (7-week and 13-week-old).
• Plants were exposed to two temperature regimes (21°C and 29°C) and inoculated with either *Rhizoctonia solani* (necrotroph), *Colletotrichum cereale* (hemibiotroph), or both.
• Disease severity was measured to evaluate infection outcomes.

Main Results:

• Coinfection had minor effects on disease metrics, contrary to expectations.
• Host age, pathogen identity, and temperature were the primary drivers of infection outcomes.
• *R. solani* lesion severity decreased with higher temperatures and was lower in older plants.
• *C. cereale* showed an age × temperature interaction, with older plants more resistant at cooler temperatures.
• Elevated temperatures reduced disease severity in coinfected plants, with a stronger effect in older plants.

Conclusions:

• Host age and environmental conditions (temperature) can outweigh within-host pathogen interactions in determining disease outcomes.
• The findings underscore the importance of considering host demographic structure when predicting plant disease responses to climate warming.
• Warming may exacerbate disease in younger plants, while older plants show varied responses depending on pathogen and temperature.