Root Infection and Systemic Colonization of Maize byColletotrichum graminicola

Abstract

Colletotrichum graminicola is a filamentous ascomycete that causes anthracnose disease of maize. While the fungus can cause devastating foliar leaf blight and stalk rot diseases, little is known about its ability to infect roots. Previously published reports suggest that C. graminicola may infect maize roots and that root infections may contribute to the colonization of aboveground plant tissues, leading to disease. To determine whether C. graminicola can infect maize roots and whether root infections can result in the colonization of aboveground plant tissues, we developed a green fluorescent protein-tagged strain and used it to study the plant root colonization and infection process in vivo. We observed structures produced by other root pathogenic fungi, including runner hyphae, hyphopodia, and microsclerotia. A mosaic pattern of infection resulted from specific epidermal and cortical cells becoming infected by intercellular hyphae while surrounding cells were uninfected, a pattern that is distinctly different from that described for leaves. Interestingly, falcate conidia, normally restricted to acervuli, were also found filling epidermal cells and root hairs. Twenty-eight percent of plants challenged with soilborne inoculum became infected in aboveground plant parts (stem and/or leaves), indicating that root infection can lead to asymptomatic systemic colonization of the plants. Many of the traits observed for C. graminicola have been previously reported for other root-pathogenic fungi, suggesting that these traits are evolutionally conserved in multiple fungal lineages. These observations suggest that root infection may be an important component of the maize anthracnose disease cycle.

Incidência de Colletotrichum graminicola em colmos de genótipos de milho

“…Os resultados obtidos no presente trabalho demonstraram que C. graminicola ocorreu em toda a extensão do colmo, com predominância no terço médio superior. A ocorrência de podridão de colmo é resultante de infecções primárias nas raízes (22) e folhas (23). Portanto, é provável que a posição em que o fungo ocorre com maior frequência no colmo esteja relacionada à origem do inóculo.…”

“…Nos casos em que houve predominância no terço superior, uma provável explicação é o fato dos feixes das folhas estarem em conexão direta com a bainha (23,24). Neste último caso, a doença ocorreria se o isolado fosse virulento à folha e ao colmo, considerando a hipótese da existência de controle genético da resistencia à antracnose distinto nas folhas e colmo, resistência essa denominada de "resistência de órgão específico" (22,23,24).…”

Entry Mode–Dependent Function of an Indole Glucosinolate Pathway in Arabidopsis for Nonhost Resistance against Anthracnose Pathogens

“…Although Colletotrichum is typically a foliar pathogen, Colletotrichum graminicola has been shown to colonize root tissue and to systemically infect above-ground stems and leaves (Sukno et al, 2008). Likewise, M. oryzae, a well-studied foliar pathogen, can also colonize roots and is capable of subsequent systemic invasion of above-ground tissues (Sesma and Osbourn, 2004).…”

“…Many fungi infect both above-ground and below-ground plant organs, of which the capacity to colonize roots is thought to represent an ancestral trait (Dufresne and Osbourn, 2001;Gunawardena and Hawes, 2002;Sesma and Osbourn, 2004;Sukno et al, 2008). Although Colletotrichum is typically a foliar pathogen, Colletotrichum graminicola has been shown to colonize root tissue and to systemically infect above-ground stems and leaves (Sukno et al, 2008).…”

“…The infection structures produced by C. graminicola and M. oryzae during root colonization resemble those of other root pathogenic fungi but are markedly different from those seen during foliar colonization. For example, germinated spores formed long "runner hyphae" on the surface of the root epidermis, and entry into root epidermal cells was initiated by lateral swellings, so-called hyphopodia, which emerge from these mature hyphae (Sukno et al, 2008). Thus, while these previous studies and our present work demonstrate the principal capacity of Colletotrichum to enter plant cells of leaves and roots independently from appressorium differentiation, tip-based entry of conidial germ tubes without appressoria on Arabidopsis leaves contrasts with the hyphopodia-based entry into root cells.…”