Defense Compounds Rather Than Nutrient Availability Shape Aggressiveness Trait Variation Along a Leaf Maturity...

Area of Science:

• Plant Pathology
• Plant-Microbe Interactions
• Fungal Genetics

Background:

• Foliar pathogens encounter diverse leaf environments based on plant maturity.
• Nutrient availability and plant defenses significantly influence pathogen success.
• Understanding the dominant factor affecting pathogen development is crucial.

Purpose of the Study:

• To determine whether nutrient availability or plant defense levels predominantly affect poplar rust fungus development.
• To investigate the impact of leaf maturity on quantitative fungal traits and leaf chemistry.

Main Methods:

• Poplar leaf disks of varying maturity were inoculated with Melampsora larici-populina using single-spore inoculation.
• Quantitative fungal traits including infection efficiency, uredinia size, and sporulation rate were measured.
• Leaf nutrient (sugars, C, N) and defense compound (phenolics) content were analyzed.

Main Results:

• Melampsora larici-populina exhibited increased aggressiveness on mature leaves, with larger uredinia and higher sporulation rates.
• No correlation was found between pathogen traits and leaf sugar, total C, or total N content.
• Phenolic compounds were negatively correlated with uredinia size and sporulation rate, suggesting a defense constraint.

Conclusions:

• Constitutive plant defense levels, particularly phenolics, more significantly constrain poplar rust pathogen fitness than nutrient availability.
• Defense compounds play a dominant role in regulating pathogen development on poplar leaves.
• Leaf maturity influences pathogen aggressiveness, primarily mediated by plant defense mechanisms.