Patterns of leaf-pathogen infection in the understory of a Mexican rain forest: Incidence, spatiotemporal variation, and mechanisms of infection

This study assessed the levels of damage by leaf pathogens and their variab ility in terms of host species, space (four mature forest sites) and season of the year (dry and rainy), and the mechanisms of infection in the unders tory of the Los Tuxtlas tropical rain forcer. Sixty-five percent of the spe cies surveyed in the dry season (N = 49) and 64.9% of those surveyed in the rainy season (N = 57) were damaged by fungi. Leaf area damaged per plant. on average, was <1% (range: 0.25-20.52%). There was considerable variation in the degree of infection among species. but not among sites and seasons. The survey showed that 43% of the leaves were damaged by herbivores and pat hogens concurrently, 16% showed damage by insect herbivory alone, and only 1.4% of the sampled leaves showed damage by pathogens alone. Pathogenicity assays experimentally confirmed that the predominant mechanism of fungal es tablishment was wounding, such as that caused by herbivory (or other simila r sources), and only rarely did infection occur through direct contact (wit hout wounds). The results revealed the omnipresence of leaf fungal infectio n, although with low damage per plant. and the importance of herbivorous in sects in the facilitation of fungal infection in tropical understory plants .