Fusarium oxysporum f.sp. melongenae Matuo & K. Ishig., (1958)

Fusarium wilt

General

• Soil pathogenic eggplant fungus described for the first time in Japan, and found in abundance in Asia: China, South Korea, Iran. Reported in Europe, especially in Italy, Spain, Greece, the Netherlands and Turkey. It was recently observed in the South-East of France (2017) and identified in 2018. Significant attacks have been reported at the scale of the same site in the Bouches du Rhône on free stumps of eggplants. Its incidence is nevertheless minimal in France because of its parasitic specificity, the majority of eggplant plants being grafted on tomato, a species not host of F. oxysporum f. sp. melongenae .
• Vascular disease specific to eggplant which can be observed in the field and under shelter.
• Once present in a farm, the fungus remains there for a long time.
• Organs attacked  : vessels, stems, leaves.
• Symptoms :
  
  • Thinning of the veins of the basal leaves (figure 1) and chlorosis and yellowing of the blade. Then progressive drying out and fall of the leaves (figures 2 and 3).
  • Surface and unilateral more or less discontinuous browning of the stem (figure 4). Quite quickly, a chancery, brownish necrotic damage develops several centimeters in length (Figure 5).
  • Browning of the vessels, darker in color than in verticillium wilt (Figures 6 and 7).
  • First partial wilting, then generalized dieback, drying out and premature death of the plant (figure 2). For some varieties, dieback can be sudden. Loss of yield.
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• Confusions possibles  : Verticillium spp., Ralstonia solanacearum .
• Signs : at the end of the course:
  • pads ( Cottony sporodochia )  (figures 8 and 9) forming abundantly on the surfaces of the stems especially, or even of the leaves. They are more or less colored, cream to pink, made up of grouped conidiophores, more or less elongated phialides producing:
    • Of microconidia hyaline oval non-septate (4.7 to 12.4 microns x 3.1 to 4.6 microns) grouped into headform (Figures 12 and 13);
    • Of macroconidia hyaline septate (3-5 partitions) sickle-shaped relatively variable size (from 9.3 to 24.8 microns x 3.1 to 6.2 microns) (Figure 12).
  • Chlamydospores round (diameter 4.6 to 5.9 .mu.m) alone and sometimes in pairs or in short chains forming from degraded roots (Figure 12).

Biology   

• Conservation : in soil on plant debris / residues and organic matter, as micro and macro conidia (from decomposed leaves and stems) and as chlamydospores and mycelium (from decomposed roots).
• Sources of inoculum : mainly contaminated soil, but also by contaminated plants .
• Infections : Conidia (macro and micro) as well as chlamydospores (figure 12) present in the soil germinate and infect the plant at the root level through wounds (induced or natural such as areas of root emissions). Then, the mycelium (figures 10 and 11) colonizes the vascular system and ends up completely obstructing the vessels and inducing the wilting of the lower leaves, then the death of the plant.
• Dissemination : ensured over short distances by dispersing the conidia present on diseased plants via contaminated water and work tools; over long distances, by wind, contaminated plants and movement of infested soil during work or plot regrouping.
• Favorable conditions : Fusarium wilt is favored by high temperatures (optimum 28 ° C). The disease would be more severe if the plants thrive in environments poor in nitrogen and phosphorus and rich in potassium and ammonia. Finally, it would also be favored by acidic, sandy soils rather than heavy soils with high pH.

Protection

• Carry out crop rotations long (at least 4 years) because the chlamydospores which are the fungus' conservation spores are able to persist for a long time in the soil.
• Use resistant varieties of eggplant * in free stems. This resistance is very common in African eggplant species.
• Use rootstocks :
  • KNVF tomato hybrids (resistance to Pyrenochaeta lycopersici , Meloidogyne spp., Verticillium dahliae and Fusarium oxysporum f. sp. lycopersici ) which are non-hosts;
  • "wild" varieties resistant to eggplant fusariosis: S. sisymbriifolium , S. torvum and S. aethiopicum g. aculeatum (also resistant to Verticillium dahliae, Ralstonia solanacearum and  Meloidogyne spp.);
  • des hybrides interspecifiques ( Solanum incanum x S. melongena and S. aethiopicum x S. melongena ).
• Disinfect particularly contaminated soils. The method used will vary depending on the country and the type of crop: steam, fumigant, fungicides , solarization.
• It may be a good idea to quickly and carefully remove the first affected plants by placing them in a plastic bag before removing them from the crop.
• The greenhouse environment and the equipment that has been in contact with diseased plants must be carefully disinfected (bleach, fumigants, various products).
• Remove and destroy plant debris to limit the persistence of the inoculum in the soil. They should not be buried under any circumstances.

* Resistance to Fusarium wilt in eggplant is monogenic. Today, three loci controlling resistance to Fusarium wilt have been identified, two on chromosome 2 of S. melongena (FM1 and Rfo-sa1, each with two allelic forms) and one on chromosome 4 . So far no strain of Fusarium oxysporum  f sp. melongenae capable of circumventing this resistance has not been detected.