Fusarium Crown Rot in Tomatoes
8/6/2012 9:37 AM
Fusarium Crown Rot is caused by the fungus Fusarium oxysporum f sp radici-lycopersici abbreviated as “ For”. In Australia it has been more prevalent in greenhouse environments, but also occurs in open field under quite specific conditions.
The fungus enters through wounds and openings caused by newly emerging roots. The first symptoms are the yellowing of the older leaves, the wilting of the plant usually in the middle of the day when the lowest fruit have reached a mature green stage, and then the permanent wilting and death of the plants. The disease is identified by the decaying of the tap root, the development of brownish water-soaked areas in the crown region of the plant. In the crown and, up about a further 15cm, the conducting tissue of the stem is discoloured dark brown. This is different from Fusarium wilt, which shows lighter discolouration all the way up the stem.
Conditions that favour Fusarium Crown Rot are cool soil temperatures in the region of 10 to 20 deg C, low soil pH, waterlogged soil and also ammoniacal nitrogen. The fungus produces three types of spores, two types which are involved in short term spread and a third which can live for a few seasons in soil or on stakes.
Rotation with non susceptible crops is essential to avoid a build up of the fungus, and stakes should be sterilised to avoid contamination of new plantings. Soil pH should be kept within the 6-7 range and ammoniacal nitrogen should be avoided.
Resistance is available out of some breeding programmes but this is generally aimed at greenhouse varieties, and in rare cases is included in the resistance package required for N Queensland. This is changing however and Lefroy Valley is in the process of first stage screening of varieties with For, Fol 1-3 & TYLCV resistance.