# Tar Spot on Maize: Impact of Soil Types and Environmental Conditions on the Survival of Phyllachora maydis in the Subtropical Climate of Florida

## TL;DR

This study examines how soil types and climate in Florida affect the survival of a maize disease-causing fungus, finding that it struggles to survive in subtropical conditions.

## Contribution

The study provides new insights into the survival of Phyllachora maydis in Florida's subtropical climate, focusing on soil and temperature effects.

## Key findings

- Ascospore germination declined over time, with 25% viability at 4 °C and 0.7% at 23 °C after eight weeks.
- Soil type had no significant effect on ascospore viability (p=0.9944).
- Higher temperatures reduced germination rates, while higher humidity increased them.

## Abstract

Tar spot, caused by Phyllachora maydis, is an established maize disease in the Midwest of the United States but remains an emerging concern in Florida. While this pathogen can overwinter on plant residue, its survival in Florida’s subtropical environment is not well understood. This study evaluated how environmental factors affect the germination of P. maydis ascospores and stroma integrity. Symptomatic maize leaves were incubated under four conditions: Histosol soil (muck), Krome soil (rocky), 4 °C, and 23 °C. Extensive leaf decomposition occurred in both soil types, with most plant material degraded after eight weeks, while the stroma maintained its structure. Despite this, ascospore germination declined across all conditions. After eight weeks, ascospores incubated at 4 °C retained 25% viability, while those at 23 °C had the lowest germination (0.7%). Ascospores from leaves buried in soil exhibited low viability (1–6%), with no significant differences between soil types (p=0.9944). Weather analysis revealed that increased temperature reduced germination rates, while higher humidity enhanced them. These findings suggest that P. maydis displays limited survivability under Florida-like conditions, with germination rates declining over time. Therefore, cultural practices such as tillage, already employed by corn producers in Florida, may be effective in reducing sources of P. maydis inoculum.