Choanephora cucurbitarum (Berk. & Ravenel) Thaxt., (1903)

Fruit rot, Choanephora fruit rot, cucurbit flower blight, melon blossom blight

- Classification: Fungi, Zygomycota, Incertae_sedis_, Incertae_sedis_, Mucorales, Choanephoraceae
- synonyms: Choanephora heterospora BS Mehrotra & MD Mehrotra (1962) [1961]; Choanephora infundibulifera f. cucurbitarum (Berk. & Ravenel) Schipper .
- dénominations anglaises : fruit rot, Choanephora fruit rot, cucurbit flower blight, melon blossom blight

C. cucurbitarum is an opportunistic fungus which has been reported in many countries distributed in tropical to sub-tropical zones : from Asia (China, India, Indonesia, Korea, Pakistan ), Africa (Benin, Congo, Ghana , Guinea, Kenya, Malawi, Mauritania, Nigeria, Senegal, Egypt ), several states in the United States, Central America and the Caribbean, South America (Brazil, Paraguay, Colombia, Peru, Venezuela) and Oceania (Australia, French Polynesia, New Caledonia ).

It does seem not to be rampant in Europe , and in particular in France.

It is likely to develop on a wide variety of hosts :
- in Cucurbitaceae; it is reported on watermelon, zucchini, various squash, pumpkin, vegetable sponge ( Luffa cylindrica );
- in other vegetables, especially chili, eggplant, radish, cauliflower, beans, peas, spinach, potatoes, but also yams, sweet potatoes, okra ;
- in various other plants, whether or not cultivated, such as amaranth, cowpea, hibiscus, fig, cotton, papaya, kilometer bean (V igna sinensis ), mung bean ( Vigna radiata ), sorghum, the manioc...

Its damage on Cucurbitaceae can occasionally be very important if the climatic conditions are lenient; in this case, it is responsible for rotting a large proportion of the fruit.


Main symptoms

C. cucurbitarum causes rots on the flowers and subsequently on the fruits of Cucurbitaceae. These are often moist and located at the tips of the fruits (Figure 1). The affected tissues, moist and soft, take on a translucent appearance and a dark tint (Figure 2). The fruits can completely liquefy in a few days.

Note that the affected organs are covered with a rather aerial blackish mold. Fruiting bodies in the form of small pinheads gradually appear. First white, they turn brown and eventually reveal a purple-black color and a shiny appearance (figure 3).

Care should be taken not to confuse this mold with that produced by a neighboring fungus, Rhizopus stolonifer , which causes quite similar symptoms on the fruits of Cucurbitaceae.

Biology epidemiology

• Conservation, sources d'inoculum

C. cucurbitarum has abilities saprophytic high and a large enzymatic arsenal which allow it to degrade a large number of substrates, plant debris and to persist in soils from year to year. It is also very polyphagous as we have indicated previously and is found on a great diversity of hosts ensuring its multiplication and its conservation.

Its chlamydospores and zygospores in particular allow it to survive.

• Penetration, invasion

C. cucurbitarum is an opportunistic fungus which settles on Cucurbitaceae in particular from senescent floral organs . For example, the wilted corollas, which persist longer than usual in humid periods, constitute nutritive bases allowing them first to settle and then secondly to colonize the fruits and cause them to rot. Stamens and pistils can also be colonized.
It can also penetrate the fruit through a wide variety of injuries: growth cracks , sunburn , apical necrosis, insect bites, various shocks, etc.)

• Sporulation and dissemination

This fungus often thrives heavily on rotten fruit. The numerous spores produced are disseminated by wind, rain and sprinkler irrigation causing ( splashing, projections of soil particles). Certain insects are said to be "vectors" of C. cucurbitarum .

• Conditions favorable to its development

Its damage is particularly serious following heavy rains. The free water present on the fruits is very conducive to its development.

C. cucurbitarum settles preferentially on weakened hosts and via "nutrient bases" or wounds. It appreciates hot and humid climates and thrives particularly well at temperatures of 25 ° C and above.


Protection methods

• During cultivation

It is often difficult to control effectively C. cucurbitarum during cultivation. However, we can recommend implementing the following measures:
- manage the best irrigation so that they are fair and never excessive;
- avoid sprinkling irrigations, otherwise perform them at the beginning or during the day to allow the plants to dry up quickly;
- if symptoms appear under shelter, it is imperative to reduce the ambient humidity by ventilating them as much as possible;
- eliminate during and at the end of cultivation the fruits more or less rotten ;
- avoid to hurt the fruit and harvest at advanced maturity.

Specific treatments fungicide are rarely necessary. Very often, they are ineffective because flowers are constantly formed and the fruits more or less buried in the vegetation are only partially protected.

• Next crop

The efficiency of crop rotations proves quite disappointing ; this situation is certainly due to polyphagia and the saprophytic potential of this fungus

The soil of the future plots of Cucurbitaceae will be well worked and drained in order to avoid the formation of puddles. In the open field, the rows of planting will be oriented in the direction of the prevailing winds so that the plant cover is well ventilated. The plants can be placed on boards. The use of plastic mulch will partially isolate the vegetation from the ground and therefore help reduce contamination.

The other diseases and pests must be controlled because they are the source of wounds and tissue necrosis conducive to the installation of C. cucurbitarum . Infected flowers and fruits should be removed and disposed of.

To our knowledge, no resistance to these fungi has been reported in cultivated Cucurbits.

Finally, note that this fungus is sensitive to the mycoparasite Piptocephalis virginiana .

* Chemical control : 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 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.