Crops
Various Oomycetes
( Pythium spp., Phytophthora spp.)
( Pythium spp., Phytophthora spp.)
Damping-off, root rots,
crown and fruit
crown and fruit
- classification : Chromista, Oomycota, Oomycetes, Saprolegniomycetidae, Pythiales, Pythiaceae, Pythium sp.
Protozoa, Alveolata, Oomycetes, Peronosporomycetidae, Peronosporales, Incertae_sedis_, Phytophthora sp.
- dénomination anglaise : damping-off, foot and root rot, buckeye rot
The Oomycetes are present in all soils worldwide and rampant wherever tomatoes are produced. The vast majority of known species are polyphagous , especially on cultivated plants.
They cause damage to tomatoes throughout their production cycle , both in nurseries on seedlings and in crops on adult plants, whether in soil or in soil. Damage can be seen on the roots, crown, lower leaves and even fruits. With the development of soilless crops, these aquatic microorganisms have found a favorite ground for their development; they are a limiting factor in production on many farms.
The sometimes intensive use of a few rare anti-Oomycete fungicides (especially metalaxyl) has led to the appearance of resistance in several species of Pythium and Phytophthora in several countries.
In France , cases of damping-off caused by Pythium spp. are mainly observed in extensive and / or poorly managed nurseries. It is mainly in soilless crops that the damage of these Chromists is sometimes spectacular. The diversity of these Oomycetes was studied in the early 2000s in the main French production areas. More than ten different species have been isolated in soilless tomato crops. The Pythium spp. are the majority, Phytophthora spp. under-represented. Note also that up to 4 different Oomycetes can be found on tomato roots and / or in the nutrient solution from the same farm. The study of their pathogenic power has revealed quite different behaviors:
- some isolates are not pathogenic, or very weakly ( Pythium torulosum, P. vexans, P. sylvaticum, P. dissotocum );
- others show moderate aggressiveness ( P. ultimun, Pythium of group F, P. intermedium );
- finally, several isolates were particularly aggressive ( P. irregularare, P. salpingophorum, P. myriotylum, P. aphanidermatum ).
P. aphanidermatum , a species ubiquitous on the roots of cucumber plants grown in soilless, is only rarely harmful on tomato. When it affects this species, it is often on farms where cucumber is also produced. It seems much more damaging above ground, especially in certain countries (Canada, South Africa, Japan ).
Among the Phytophthora , P. nicotianae is the most present species in the field in France. It is responsible for attacks on seedlings in nurseries and at planting in soil crops planted in the open field and sometimes under cold shelters. In soilless culture, it does not seem to be able to express itself with gravity. Its accidental introduction into this type of crop, via contaminated plants, did not allow us to observe any significant damage thereafter. This does not appear to be the case in other countries where its damage is reported in soilless crops, notably in Germany. This Phytophthora is rather known in our country for the significant damage it causes on the fruits of field crops intended for the canning industry in particular. Its species name is quite controversial, many synonymies exist. It should be noted that several isolates have been reported from around the world, diverging in their aggressiveness and virulence towards more or less diverse host ranges. The tomato appears to be rather susceptible to a high proportion of these isolates.
If we are interested in the frequency of Oomycetes observed in soilless crops in our country, we note that in fact, only isolates of Pythium group F are widely present in the field, in almost the majority of farms. It should be noted that the aggressiveness on tomato of the isolates studied is very variable. The other Oomycetes, whether Pythium or Phytophthora , are only found very occasionally or in a rather limited number of cultures.
The many species of Pythium and Phytophthora pathogenic on tomato are treated in the same sheet (except Phytophtora infestans ) for at least three reasons: their biological characteristics and the symptoms which they cause are quite comparable, their development is often influenced by the same conditions and the protection methods implemented to control them are identical.
* There are about 800 saprophytic or parasitic species of Oomycetes which have long been classified as Phycomycetes or “lower fungi” (Eumycetes). This classification was revised a few years ago because the ultrastructure of these microorganisms, their biochemistry and their molecular sequences indicated that they belonged to the Chromists, including mainly algae (green and brown), diatoms Currently, depending on bibliographic sources, they can be associated either with the reign of the Chromista (Index fungorum), or with the reign of the Stramenopila (Tree of life).
They cause damage to tomatoes throughout their production cycle , both in nurseries on seedlings and in crops on adult plants, whether in soil or in soil. Damage can be seen on the roots, crown, lower leaves and even fruits. With the development of soilless crops, these aquatic microorganisms have found a favorite ground for their development; they are a limiting factor in production on many farms.
The sometimes intensive use of a few rare anti-Oomycete fungicides (especially metalaxyl) has led to the appearance of resistance in several species of Pythium and Phytophthora in several countries.
In France , cases of damping-off caused by Pythium spp. are mainly observed in extensive and / or poorly managed nurseries. It is mainly in soilless crops that the damage of these Chromists is sometimes spectacular. The diversity of these Oomycetes was studied in the early 2000s in the main French production areas. More than ten different species have been isolated in soilless tomato crops. The Pythium spp. are the majority, Phytophthora spp. under-represented. Note also that up to 4 different Oomycetes can be found on tomato roots and / or in the nutrient solution from the same farm. The study of their pathogenic power has revealed quite different behaviors:
- some isolates are not pathogenic, or very weakly ( Pythium torulosum, P. vexans, P. sylvaticum, P. dissotocum );
- others show moderate aggressiveness ( P. ultimun, Pythium of group F, P. intermedium );
- finally, several isolates were particularly aggressive ( P. irregularare, P. salpingophorum, P. myriotylum, P. aphanidermatum ).
P. aphanidermatum , a species ubiquitous on the roots of cucumber plants grown in soilless, is only rarely harmful on tomato. When it affects this species, it is often on farms where cucumber is also produced. It seems much more damaging above ground, especially in certain countries (Canada, South Africa, Japan ).
Among the Phytophthora , P. nicotianae is the most present species in the field in France. It is responsible for attacks on seedlings in nurseries and at planting in soil crops planted in the open field and sometimes under cold shelters. In soilless culture, it does not seem to be able to express itself with gravity. Its accidental introduction into this type of crop, via contaminated plants, did not allow us to observe any significant damage thereafter. This does not appear to be the case in other countries where its damage is reported in soilless crops, notably in Germany. This Phytophthora is rather known in our country for the significant damage it causes on the fruits of field crops intended for the canning industry in particular. Its species name is quite controversial, many synonymies exist. It should be noted that several isolates have been reported from around the world, diverging in their aggressiveness and virulence towards more or less diverse host ranges. The tomato appears to be rather susceptible to a high proportion of these isolates.
If we are interested in the frequency of Oomycetes observed in soilless crops in our country, we note that in fact, only isolates of Pythium group F are widely present in the field, in almost the majority of farms. It should be noted that the aggressiveness on tomato of the isolates studied is very variable. The other Oomycetes, whether Pythium or Phytophthora , are only found very occasionally or in a rather limited number of cultures.
The many species of Pythium and Phytophthora pathogenic on tomato are treated in the same sheet (except Phytophtora infestans ) for at least three reasons: their biological characteristics and the symptoms which they cause are quite comparable, their development is often influenced by the same conditions and the protection methods implemented to control them are identical.
* There are about 800 saprophytic or parasitic species of Oomycetes which have long been classified as Phycomycetes or “lower fungi” (Eumycetes). This classification was revised a few years ago because the ultrastructure of these microorganisms, their biochemistry and their molecular sequences indicated that they belonged to the Chromists, including mainly algae (green and brown), diatoms Currently, depending on bibliographic sources, they can be associated either with the reign of the Chromista (Index fungorum), or with the reign of the Stramenopila (Tree of life).