Monthly Archives: November 2020

Soybean anthracnose

Soybean (Glycine max) anthracnose is caused by several Colletotrichum species, including C. truncatum, C. destructivum, C. coccodes, C. chlorophyti, C. gloeosporioides, C. incanum, C. plurivorum, C. sojae, C. musicola and C. brevisporum; being C. truncatum the most studied species until now.

The dissemination of the disease to new areas occurs mainly by contaminated soybean seeds, and there are evidences of off-season survival due the production of fungal resistance structures, called microsclerotia. Anthracnose symptoms can appear since the sowing until the final reproductive stages of soybean in the field. It is known that Colletotrichum species can go through a quiescent phase in the plant, but differences in timing of appearance of the disease are not yet fully understood.

Typical soybean anthracnose symptoms are pre and post-emergence damping-off; irregular, dark and depressed lesions that can appear in all the tissues of the plant and dark lesions on laminar veins on leaves. The consequence of those symptoms are the reduction of stand, early defoliation and opening of pods; all of those causing significant reduction of soybean production in years with warm and humid conditions, when anthracnose can reach up to 100% of incidence. 

Figure 1: Typical symptoms and signs of C. truncatum on soybean. Infected seed (A); irregular, dark and depressed lesions on cotyledons, leaves, petiole, stem and pods (B; D-E); premature opening of pods with infected seeds (C). (Boufleur et al., under review).

Control measures for soybean anthracnose should start with sowing disease-free seeds, and the application of cultural practices like crop rotation. Some chemical molecules are available to be used alone or in mixtures, that can be used on seed treatments and spraying of plants. However, several studies on the efficiency of the chemical control showed the lack of efficiency of some of those, and therefore they need to be constantly updated. Besides the potential of destruction and the increasing reports of the disease in soybean production regions all over the world, until now there are no breaded soybean cultivars resistant to anthracnose.

A lot of effort still needs to be done to better understand the complexity of this disease and the role of all the Colletotrichum species reported until now associated with soybean.

More information about soybean anthracnose and questions that still need to be answered can be found at Boufleur et al., 2020 (under review).