Nitrogen fertilisation and substrate pH effects on corky root disease (Pyrenochaeta lycopersici) in greenhouse tomatoes

Abstract

Corky root disease is becoming increasingly important in organic tomato production. The effects of ammonium-dominated, nitrate-dominated or balanced nitrogen fertiliser on corky root were studied in greenhouse tomatoes. The lowest disease index occurred in tomatoes with the ammonium-dominated fertiliser and the highest with the balanced nitrogen fertiliser. Disease incidence increased with increasing nitrogen level and disease severity with increasing pH value of the soil-substrate. In complementary in vitro studies, the highest mycelial growth rate of Pyrenochaeta lycopersici was observed on balanced nitrogen medium (50% nitrate: 50% ammonium) and the lowest in the nitrate-dominated medium. Regarding pH, the highest mycelial growth occurred at the optimum pH for tomato growth (pH range 5.0–6.5). No practical advice concerning fertiliser composition was possible because no treatment achieved satisfactory control of corky root. However, N fertilisation of organic greenhouse tomatoes should be based on calculated nutrient uptake by the crop.