Phomopsis sclerotioides is conserved in plots or substrates thanks to the numerous pseudo-sclerotia (figure 1) and pseudo-stromas (figure 2) that it produces on the affected roots. They allow it to persist in the soil for several years. It can be hosted by several Cucurbitaceae (cucumber, zucchini, squash, watermelon ... ). In France, it attacks mainly cucumber and, to a lesser extent, melon.

 

It seems that it settles on the root system through the rootlets that it colonizes before reaching the roots. It gradually invades the tissues of the cortex which eventually break down and disappear, as well as the central cylinder.

 

On infested tissues, it produces pseudo-stromas and pseudo-microsclerotia which ensure its conservation and probably its dissemination. The modalities of the latter are not fully known. Indeed, this fungus is capable of producing pycnidia in vitro providing numerous spores and being able to ensure its dispersion. These are never observed on the roots. However, dissemination is possible. In fact, P. sclerotioides is already capable of colonizing soils very quickly, all the more quickly when they have been disinfected. It is also rampant in some nurseries, so it can be carried by contaminated plants. All tools and equipment coming into contact with contaminated soil and carrying soil propagules are liable to disseminate it.

 

They are not well known. It appears to be particularly damaging in relatively cool and moist soils, causing numerous necrotic lesions. When temperatures rise, its parasitic activities appear weaker; on the other hand, it would produce many more pseudo-sclerotia and pseudo-stromas under these conditions.

The disease is particularly expressed on plants loaded with fruit as harvest approaches.