Novel insights into the early stages of infection by oval conidia of Colletotrichum sublineolum

Ednéia Aparecida De Souza-Paccola,José Edson Fontes Figueiredo,Francisco André Ossamu Tanaka,Cleide Aparecida Bomfeti,Luzia Doretto Paccola-Meirelles,Nelson Barros Colauto,Nelson Sidnei Massola Junior

doi:10.1590/0103-9016-2014-0409

Ednéia Aparecida De Souza-Paccola, José Edson Fontes Figueiredo + Show 5 more

Open Access

https://doi.org/10.1590/0103-9016-2014-0409

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Abstract

Anthracnose, caused by Colletotrichum sublineolum Henn. ex Sacc. & Trotter, is one of the most important sorghum [Sorghum bicolor (L.) Moench] diseases in Brazil. This fungus exhibits conidial dimorphism, producing either falcate or oval conidia on solid and liquid media, respectively. We compared patterns of the initial infection events by these two types of conidia on sorghum leaves using light microscopy and scanning electron microscopy. The infection events during the first 24 h were similar for both oval and falcate conidia. Globose and melanized apressoria were formed at 24 h after inoculation (hai) regardless of the conidia type. Dense mycelium and oval conidia developed from germinated falcate conidia at 32 hai. Hyphal mass displaying acervuli filled with falcate conidia and surrounded by setae, developed from germinated oval conidia at 48 hai. Oval conidia were as capable as falcate conidia of infecting sorghum leaves. The inherent ability to grow faster and the easeness with which oval conidia can be produced in vitro as compared to falcate, make the former a preferred choice for studies on the C. sublineolum-sorghum interaction. It would be instructive to further investigate the potential role of the oval conidia in epidemics.

Highlights

Anthracnose, caused by Colletotrichum sublineolum Henn. ex Sacc. & Trotter, is one of the most important diseases affecting sorghum [Sorghum bicolor (L.) Moench] crops (Wang et al, 2006; Perumal et al, 2009)
scanning electron microscope (SEM) analysis of oval conidia on sorghum leaves Results of the SEM analysis corroborated those of the light microscopy analysis and provided additional information on the initial infection events
A dense mycelium developed on the leaf surface from germinated falcate conidia at 32 hai, and high density of oval conidia was observed (Figure 1E)

Summary

Introduction

Anthracnose, caused by Colletotrichum sublineolum Henn. ex Sacc. & Trotter, is one of the most important diseases affecting sorghum [Sorghum bicolor (L.) Moench] crops (Wang et al, 2006; Perumal et al, 2009). Disease symptoms are characterized by the formation of elliptic and circular lesions, up to 5 mm in diameter, with reddish, orangish, dark purple or brown edges, depending on the cultivar. A second type of conidia, the oval conidia, was found in C. sublineolum (Souza-Paccola et al, 2003) They are smaller than falcate conidia, oval to elliptic in shape and, the falcate conidia are more common in this species, the oval conidia are easier to produce in vitro than the falcate conidia. The latter are produced in solid culture and are light-dependent, whereas the oval conidia are produce in liquid culture only and they are light-independent

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