Eggplant - Pyrenochaeta lycopersici

Pyrenochaeta lycopersici coccodes (Wallr.) S. Hughes, (1958)

RW Schneid. & Gerlach, (1966)

Cork root disease

General

Telluric fungus mainly studied on tomatoes, first described in Europe, is now present in production areas on several continents. It is a marker of so-called “tired” soils which have supported in particular crops of tomatoes on several occasions and / or other sensitive crops, mainly vegetables.
Reported in organic and mineral substrates of soilless cultures, although it does not have structures allowing it to spread easily.
Little damaging on ungrafted eggplant, normally not without incidence when it is grafted on KNVF type rootstock.
affecting in particular crops under cover in soil.
The "monoculture" of ungrafted eggplant plants can generate an increase in its incidence.
It is especially part of a root parasitic complex of several soil pests classified according to their decreasing incidence: Colletotrichum coccodes , Meloidogyne spp., Phytophthora nicotianae , Pyrenochaeta lycopersici , Rhizoctonia solani, Globodera tabacum .
Colonizes or recolonizes disinfected soils rather slowly, which is why this practice is effective over a relatively long period of time, as long as the method or fumigant has been chosen with care.
Three groups of strains would have been defined according to their thermal optima: cold, temperate and hot strains. These groups do not seem to present a great molecular variability according to the scarce work on the subject.
Organs attacked : mainly the roots in a very partial and localized way on aubergine in France.
Symptoms :
- Lesions on rootlets, particularly sensitive, which turn brown, degrade quickly and disappear.
- The roots locally reveal brown and smooth changes at first, then they become superficially corky; A few slightly swollen, cracked and dry-looking sleeves then appear (figure 3).
- Generally, the presence of Pyrenochaeta lycopersici on the roots of the eggplant does not lead to a reduction in plant growth, or even their dieback, as can be the case on tomatoes.
>>> More pictures
Signs : unusually irregularly sized pycnidia, producing ellipsoid conidia of 4-6 x 1-1.5 µm (figure) with setae on damaged roots.
Possible confusion : Colletotrichum coccodes .

Biology

Storage : keeps for several years in the soil on plant debris thanks to its mycelium and its chlamydospores. Various cultivated alternative hosts, entering in rotation with the eggplant have been able to accommodate and multiply it: in particular the ungrafted tomato, lettuce, melon, cucumber, pepper, bean, watermelon, spinach, strawberry, Carthamus tinctorius. ?? It is the same for several weeds. Note that this fungus, although it grows very slowly in the soil, can reach the deep layers.
Sources of inoculum : its mycelium and its chlamydospores.
Infection : its mycelium penetrates directly into the root tissues or via wounds. and colonizes the cortex
Development, sporulation : rapidly colonizes the tissues of the cortex thanks to its mycelium, gradually leading to its rotting or suberization. It exceptionally forms irregularly sized pycnidia, producing ellipsoid conidia of 4-6 x 1-1.5 µm (Figure 1) and bearing setae on weathered tomato roots.
Dissemination : Given the rarity of these pycnidia, it can be assumed that these structures do not contribute much to the dissemination of P. lycopersici . The dispersal potential of this fungus is therefore very limited and depends above all on the activities linked to the cultivation of tomatoes, or even eggplant. Thus, the dissemination can be carried out by means of plants and / or substrates. contaminated, tools and implements.
Favorable conditions : it is rather known to develop in cold climatic conditions, the “cold” strains having a thermal optimum between 15-20 ° C (northern European strains); "hot" strains are still pathogenic at 26-30 ° C. The latter are found in particular in several countries of the Mediterranean Basin (Tunisia, Lebanon, etc.). The monoculture of tomatoes and / or the alternating or non-alternating production of sensitive crops in the same plot increases the rate of inoculum of the soil and favors its extension therein.

Protection

Carry out preventive crop rotations, before the soil is heavily contaminated. They should last at least 3 to 4 years. Of course, other plants entering the rotation will not be susceptible. In addition, weeds likely to harbor the fungus will be eliminated from the plots.
Disinfect heavily contaminated soils (solarization, biofumigation, fumigant, etc.).
Disinfect or replace the bags, pots, gutters of infested soilless crops.
Choose a draining, well-worked soil: a good subsoil will allow the roots to access new layers.
In the nursery, use healthy substrates (disinfected) and avoid placing the clods on the ground. Indeed, they often become contaminated in contact with the latter, in particular if it has not been disinfected.
In the presence of wilting during cultivation, which is rare on eggplant, try to keep the plants alive as long as possible; for this it is appropriate:
- to butter them in order to promote the emission of adventitious roots which can replace the old damaged roots. In soil-less cultivation (on peat or on pozzolan + peat) and during serious attacks, peat can be added locally to the collar to allow additional rooting. Sawdust is sometimes used;
- to bathe them during the hottest periods of the day to avoid excessive and uncompensated evaporation, leading to wilting, drying out and death of the plants;
- carefully monitor irrigation. Indeed, if the plants wither, it is not necessarily linked to a lack of water, but rather to root alterations due to telluric pests associated with P. lycopersici . In some cases, growers tend to increase irrigation to respond to wilting, leading to amplification of root lesions through asphyxiation.
Eliminate and carefully destroy diseased plants and their root system during and at the end of cultivation.
Grafting is an eminently effective solution, especially for crops under cover and for hobbyist gardens. Several intra or interspecific hybrid rootstocks are currently available.