Background:

Little is known on factors determining infection of tropical plants by fungal pathogens, although multiple studies on model species show that light conditions affect the two major hormones that control resistance in plants to enemies. This is the first study using a natural population of a wild tropical plant to relate light conditions to resistance hormones and, the beneficial and detrimental interactions with insects and fungi.

Hypothesis:

Light conditions affect the endogenous levels of resistance hormones and thereby cause quantitative shifts among herbivores and nectrotrophic, biotrophic and endophytic fungi.

Studied species:

The tropical vine Syngonium podophyllum.

Study site:

Los Tuxtlas tropical rain forest, Mexico.

Methods:

We used GC-MS to quantify the concentration of the two resistance hormones in intact leaves and natural levels of herbivory and fungal disease in S. podophyllum plants growing naturally in the full sun or in the shade.

Results:

The proportion of leaves damaged by herbivores or infected by hemibiotrophic or necrotrophic pathogens was higher in shade than under full-light conditions. Damage caused by biotrophic pathogens was frequently observed in sun but not in shade. Levels of both hormones in phenotypically healthy leaves were higher in sun than in shade.

Conclusions:

(i) light has an effect on concentrations of plant resistance hormones in nature; (ii) these differences have consequences for fungi and animals that naturally interact with the plant, and (iii) the described effect can represent a physiological mechanism via which an abiotic factor affects the members of the guilds at higher trophic levels.

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