Compost induces protection against Fusarium oxysporum in sweet basil

Sweet basil (Ocimum basilicum L.) plants suffer frequently from wilt caused by Fusarium oxysporum f. sp. basilici (FOB). No efficient fungicide is currently available to control the disease. Sweet basil transplants were grown in either sphagnum peat (Europlant, Germany) or in compost, made by mixing the coarse fraction of cattle manure, chicken manure and wheat straw. The C/N ratio of the original mixture was 22.5; this fell to 14.3 after maturation. Uniform and healthy sweet basil transplants were selected. Their roots were cut before planting and treated either with distilled water or with suspensions containing various concentrations of Fusarium microconidia. The treated cuttings were planted in 0.5-1 pots filled with the same substrates. First wilt symptoms appeared one week later. Visual inspections were made for an additional 2-3 weeks, during which inoculated plants either died or exhibited a certain degree of stunted growth. At the end of this period, the above-ground plant parts were harvested and weighed. The tested compost induced protection against F. oxysporum f. sp. basilici and reduced the severity of the visual symptoms Of Fusarium wilt, as compared with plant grown on peat moss. Compost enhanced plant development, either with or without inoculation, in spite of the fact that compost-grown plants were not fertilized from sowing till the end of the experiment, whereas peat-grown plants were fertilized. This experiment was replicated twice with consistent results. Autoclaving the compost nullified its suppressive effect towards Fusarium. Autoclaving peat moss, without subsequent inoculation with Fusarium, promoted plant growth, suggesting that other, yet to be identified, pathogen(s) may be responsible for the inferiority of peat moss compared with compost. (C) 2002 Elsevier Science Ltd. All rights reserved.