Incidence of Fungal Necrotrophic and Biotrophic Pathogens in Pioneer and Shade-tolerant Tropical Rain Forest Trees

Abstract

This study assessed the hypothesis that plant life history traits determine the incidence of fungal biotrophic and necrotrophic pathogens in pioneer vs. shade-tolerant tropical plant species. Considering that pioneer species mainly invest in induced defenses, we expected a negative relationship between the incidence of biotrophic and necrotrophic pathogens; in contrast, as shade-tolerant species invest heavily in constitutive defenses, we expected to find no correlation between the incidence of biotrophic and necrotrophic pathogens. These ideas were evaluated by assessing standing levels of fungal damage in a set of pioneer and shade-tolerant species from the Lacandona tropical rain forest (Mexico). The results showed that among pioneer plant species, leaves with biotrophic lesions were between 34 and 44 percent more abundant than those with necrotic lesions. In contrast, among shade-tolerant species, the proportions of leaves with necrotic lesions were 17–23 percent higher than those of leaves with injuries caused by biotrophic pathogens. Our study suggests that tropical tree species might present different defense strategies depending on the life-style of the pathogens that attack them, and the life history strategy of the attacked host plant species. Thus, the host constitutive and induced defenses, as well as the mechanisms used by different types of pathogens to circumvent those defenses maybe responsible for the patterns of attack observed in perennial tropical plants. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp. Se evaluó la hipótesis de que las estrategias de historia de vida de las plantas tropicales (pioneras y tolerantes a la sombra) determinan la incidencia de hongos patógenos biotróficos y necrotróficos. Si se considera que las especies pioneras invierten principalmente en defensas inducidas, se esperaría una relación negativa entre la incidencia de hongos patógenos biotróficos y necrotróficos. En contraste, las plantas tolerantes a la sombra invierten principalmente en defensas constitutivas y esperaríamos una ausencia de correlación entre la incidencia de hongos biotróficos y necrotróficos. Estas ideas se evaluaron mediante la medición de los niveles de daño causados por hongos patógenos biotróficos y necrotróficos en una serie de especies pioneras y tolerantes a la sombra en la selva alta perennifolia de la Lacandona (México). Los resultados indican que entre las especies pioneras, las hojas atacadas por hongos patógenos biotróficos fueron entre 34 y 44% más abundantes que aquellas atacadas por patógenos necrotróficos. En contraste, en plantas tolerantes a la sombra, la proporción de hojas que mostraron lesiones necróticas fue entre 17 a 23% mayor que la de hojas afectadas por lesiones biotróficas. Este estudio sugiere que las especies de árboles tropicales pueden presentar diferentes estrategias defensivas dependiendo de sus propias estrategias de historia de vida así como de las de los hongos patógenos que las atacan. Por lo tanto, las defensas constitutivas e inducidas de las plantas hospederas, así como los mecanismos usados por los diversos tipos de patógenos para evitar dichas defensas podrían ser responsables de los patrones de ataque observados en plantas tropicales perennes. TABLE S1. List of the studied plant species, including family, life history and the fungal pathogens associated with their foliage in the Chajul Field Station. TABLE S2. Fungal genera isolated from the studied plant species in the Chajul Field Station. TABLE S3. List of host-plant species that tested positive within seven days after experimental inoculation in the Chajul Field Station. Please note: Wiley-Blackwell is not responsible for the content or functionality of any supporting materials supplied by the authors. Any queries (other than missing material) should be directed to the corresponding author for the article. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.