Single and combined effect of two fungal diseases on growth of moth plant, Araujia hortorum (Apocynaceae).
Araujia hortorum is a perennial, broad-leaved herbaceous climber native to South America considered an invasive weed in New Zealand and several other countries where it has been introduced. Ascochyta araujiae and Septoria araujiae are the causal agents of two of the most frequently encountered diseases affecting natural populations in Argentina, which on many occasions co-occur on the same plant. Host-pathogen interactions generally result in a decrease in host fitness. However, when two or more pathogens occur simultaneously on a single host the outcome of the combined interaction might be different from the sum of each acting individually. An experiment was conducted to investigate the single and combined effect of the two pathogens on growth of the host plant as compared with healthy control ones. Each pathogen individually, as well as the combination of both, had a significant effect on size and biomass production of diseased plants. The interaction of both diseases resulted in biomass reductions similar to those of A. araujiae acting alone. This is because A. araujiae, having a shorter latent period, induces earlier defoliation causing the loss of latent S. araujiae infections that never develop. The implications of these findings on the potential use of these pathogens as biological control agents are discussed.