Submitted to: American Journal of Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/13/2010
Publication Date: 11/17/2010
Publication URL: http://handle.nal.usda.gov/10113/60860
Citation: Bowling, A.J., Vaughn, K.C., Hoagland, R.E., Stetina, K.C., Boyette, C.D. 2010. Immunohistochemical investigation of the necrotropic phase of the fungus Colletotrichum gloeosporioides in the biocontrol of Hemp sesbania (Sesbania exaltata; Papilionaceae). American Journal of Botany. 97(12):1915-1925. doi:10.3732/ajb.1000099. Interpretive Summary: The biocontrol fungal strain known as Lockdown may attack more weed species by changes to the formulation. Little knowledge has been obtained as to how this strain causes the death of the weed. In this study, scientists from the Crop Production Systems Research Unit and the Biological Control of Pests Research Unit showed that the fungus induces a massive loss of pectins in the wound site, causing cellular collapse and eventual death of the plant. The degraded pectins also induce some host defense response in the weed.
Technical Abstract: Fungal plant pathogens exert much of their effect on plant cells through alterations in the host cell walls. However, biochemical proof for this change is difficult because of the relatively small number of cells that are affected by the pathogen in the bulk of host tissue. In this study, we examined the differences between infected and uninfected areas of hemp sesbania (Sesbania exaltata [Rydb.] ex A.W. Hill) seedlings that have been treated with the biocontrol agent Colletotrichum gloeosporioides (Penz.) Penz & Sacc. The lesions on the stems consisted of a necrotic area with tissue disruption occurring through several layers of cells. To determine the changes in cell wall composition, semi-thin sections were probed with using a battery of antibodies. Changes occurred due to both the loss of specific polysaccharides by the fungal invasion and responses of the plant to ward off the fungal invasion. At the invasion site, there was significant loss of some rhamnogalacturon-1 (RGI) and both esterified and de-esterified homogalacturonan (HG)-reactive epitopes. In contrast, tissues between the vascular tissue and the fungal lesion were shown to react more strongly with antibodies that recognize arabinogalactan proteins (AGPs) and xyloglucans than in unaffected areas. These data strongly indicate the role of pectinases in the invasion of the biocontrol agent and the importance of extensins, AGPs and xyloglucans as defense by the host.