Crops
Thanatephorus cucumeris (Rhizoctonia solani , Rhizoctone brun)
Thanatephorus cucumeris , widely distributed in the world and in France, is very common, even almost permanent, in many market garden soils. It can be considered as a biological marker of so-called “tired” soils. It is therefore not surprising that it affects the tomato, on which it can cause various symptoms, on almost all organs.
Like Pythium spp., This soil fungus particularly appreciates young seedlings after sowing and causes damping -off . Both before and after emergence, brown, reddish-brown to black lesions are visible on affected seedlings. Once these last out of the ground, the alterations are mainly localized on the crown, causing the death of the young seedlings.
This fungus is also capable of attacking plants in the active growth phase, even adults. Again, it can affect the roots and crown of this nightshade. On the roots, the nature of the symptoms noted seems to be influenced by the cultural context and in particular the humidity of the soil. It is not uncommon to see this fungus associated with tomato roots that are lightly suberized on the surface, rather "dry", on which many rootlets have disappeared. In this case, however, it is not always easy to know if it is only a simple biological marker of root systems that have undergone agro-cultural or climatic stress. It is also found on root systems with rather damp reddish-brown lesions and / or similar rot ( Rhizoctonia root rot ) . In this situation, the degraded cortex can break off in places. Note that it also attacks tomato rootstocks of the KNVF type.
Note that R. solani can be observed at the same time as Colletotrichum coccodes , Pyrenochaeta lycopersici , phytophagous nematodes on the roots of tomatoes grown in soil. It is sometimes found in soilless cultures, in complex with Pythium spp., Fusarium oxysporum f. sp. radicis-lycopersici, and Colletotrichum coccodes .
It also affects the neck ( basal stem canker ), the stem and many aerial organs of the tomato.
Whatever the nature and location of the symptoms, the septate and hyaline to brown mycelium of R. solani , traveling on or near the injured tissues, reflects its presence (Figures 1 and 2).
For more information on this fungus, you can consult the sheet Thanatephorus cucumeris (Rhizoctonia solani ) fact .
Like Pythium spp., This soil fungus particularly appreciates young seedlings after sowing and causes damping -off . Both before and after emergence, brown, reddish-brown to black lesions are visible on affected seedlings. Once these last out of the ground, the alterations are mainly localized on the crown, causing the death of the young seedlings.
This fungus is also capable of attacking plants in the active growth phase, even adults. Again, it can affect the roots and crown of this nightshade. On the roots, the nature of the symptoms noted seems to be influenced by the cultural context and in particular the humidity of the soil. It is not uncommon to see this fungus associated with tomato roots that are lightly suberized on the surface, rather "dry", on which many rootlets have disappeared. In this case, however, it is not always easy to know if it is only a simple biological marker of root systems that have undergone agro-cultural or climatic stress. It is also found on root systems with rather damp reddish-brown lesions and / or similar rot ( Rhizoctonia root rot ) . In this situation, the degraded cortex can break off in places. Note that it also attacks tomato rootstocks of the KNVF type.
Note that R. solani can be observed at the same time as Colletotrichum coccodes , Pyrenochaeta lycopersici , phytophagous nematodes on the roots of tomatoes grown in soil. It is sometimes found in soilless cultures, in complex with Pythium spp., Fusarium oxysporum f. sp. radicis-lycopersici, and Colletotrichum coccodes .
It also affects the neck ( basal stem canker ), the stem and many aerial organs of the tomato.
Whatever the nature and location of the symptoms, the septate and hyaline to brown mycelium of R. solani , traveling on or near the injured tissues, reflects its presence (Figures 1 and 2).
For more information on this fungus, you can consult the sheet Thanatephorus cucumeris (Rhizoctonia solani ) fact .
Figure 1
Figure 2