Determinants of disease expression and survival of infected individual fronds in wild populations of Mazzaella laminarioides (Rhodophyta) in central and southern Chile

This study provides evidence that the expression of a deformative disease in wild populations of the red algal host Mazzaella laminarioides is strongly influenced by exogenous factors. This was particularly the case for a population in Matanzas, Chile, whose members developed the symptoms when they grew in a high-infection zone, regardless of their history of susceptibility to the disease. However, our results for between locality transplants suggest that a genetic component may be playing a role in the expression of the disease. Plants transplanted from one locality to another did not reach the same levels of disease expression as their indigenous local counterparts. Infectious diseases seem to affect the survival of the infected hosts, an effect that varies depending on the pathogen involved, the season and the locality under consideration. In addition to the direct impacts of the 2 diseases (green patch disease caused by Endophyton ramosum and the deformative disease associated with Pleurocapsa sp.) affecting Mazzaella laminarioides, the deformative disease caused an increased susceptibility to grazing, which may accelerate the direct negative impact of the pathogen itself.