Myrothecium roridum

Tode (1790)

- Classification: Fungi, Basidiomycota, Lichinomycetes, Hypocreomycetidae, Hypocreales, Incertae_sedis_
- téléomorphe : Hypocreales
- synonyms: Halocarpus roridum (Tode) Link, (1809); Myrothecium newcomer Saca., (1908)
- English name: myriothecium rot, myriothecium rind rot, myrothecium leaf spot, crater rot



M. roridum is considered to be an optional soil-borne parasitic fungus, widely distributed throughout the world in temperate and tropical regions, and capable of attacking many hosts, more than 263 have been identified.
It has been described several times on Cucurbitaceae: cucumber, melon , watermelon, squash, West Indian cucumber ( Cucumis anguria ). Note that another species, Myrothecium verrucaria , has been reported on cucumber, as on tomato.

This fungus is present in France, but does not seem to affect Cucurbitaceae to our knowledge.


Main symptoms

M. roridum is able to cause symptoms on leaves, stems and fruits.

The leaves of Cucurbitaceae show rather circular dark brown spots (Figures 1 to 6), sometimes revealing concentric (Figure 3) and coalescing patterns.

More or less canker lesions may develop at the neck and on the stem .

It causes deterioration on the fruits in pre and post-harvest. On melon, they have a rather circular shape, a dark color and are more or less concave, measuring several centimeters in diameter. The underlying flesh gradually rots. Superficial tissue can rupture.

On the altered parts, M. roridum fruits in the form of discrete grayish to black masses (sporodochia) (Figure 7).


Biology, epidemiology

• Conservation, sources d'inoculum

M. roridum is able to remain in the soil in a saprophytic state on organic matter. It is an optional parasitic fungus of many plants, whether cultivated or not, which can ensure its multiplication and contribute to its conservation. It affects in particular: red clover, coffee, cotton, peanuts, soybeans, rapeseed, sunflower, rice, various ornamental plants (sainpaulia, gardenia, dieffenbachia, ficus, delphinium, lantana, petunia, anthurium, gerbera ...) ... On vegetables, it is reported on tomato fruits, eggplant, lettuce, beans ...

• Penetration, invasion

The first stages of its parasitic process on Cucurbitaceae are not described in the literature.

• Sporulation and dissemination

M. roridum fruits on injured tissue and produces numerous spores that cluster together in the form of grayish to black sporodochia (Figures 7 and 8). Its conidia (Figures 9 and 10) are probably disseminated by splashing water, wind, or even certain insects.

This fungus is preserved and disseminated via seeds, in particular on watermelon, calabash, loofah, pumpkin ...

• Conditions favorable to its development

The humid and hot climatic conditions favor its development. The germination of its conidia is optimal at 28 ° C.


Protection methods

In countries where it is rife, it is advisable to use healthy seeds or to disinfect them. Diseased plants and fruits, as well as plant debris, should also be removed.

Fungicide treatments * are recommended at the time of flowering.

The harvested fruits must be refrigerated quickly.

Differences in sensitivity were observed between cultivars of melon, without very high level resistance being found.

* Chemical control : As the number of pesticides available for a given use is constantly changing, we advise you to always confirm your choice by consulting the e-phy site of the Ministry of Agriculture and Fisheries which is an online catalog of plant protection products and their uses, fertilizers and growing media approved in France. This also applies to all biological products based on microorganisms or natural substances.