Factors associated with suppression of Fusarium basal rot of onion in New Zealand soils: literature review and greenhouse experiments

Fusarium basal rot, caused by Fusarium oxysporum f.sp. cepae, is an important onion disease worldwide. Greenhouse pot experiments were conducted during two growing seasons to determine if field soils from New Zealand's main onion growing regions had different fusarium basal rot suppressive capabilities, and identified factors involved in disease suppression This study demonstrated that soils naturally suppressive to fusarium basal rot were present in New Zealand and that soil organic matter content, total soil carbon, total nitrogen and soil phosphorous concentrations were associated with disease incidence. Soil microorganisms were shown to be involved in disease suppression since when they were eliminated or reduced by soil heat treatment, fusarium basal rot incidence markedly increased. This study provided an increased understanding of how soil physical, chemical and biological factors affect the suppressiveness of selected New Zealand soils to fusarium basal rot of onion, and demonstrated that certain bacterial and fungal taxa may be involved in suppression of this disease.