Genetic Characterisation and Aggressiveness of the Fusarium oxysporum Species Complex in Tomato Plants and Irrigation Water From Australian Processing Fields

Abstract

Fusarium oxysporum Species Complex (FOSC) includes important soil‐borne pathogens of a range of crops worldwide. In Victoria and New South Wales, Australia, FOSC has been identified as the cause of stunting and poor growth in processing tomato fields, resulting in significant yield losses. A total of 40 FOSC isolates were obtained from symptomatic tomato plants, irrigation water samples and culture collections, which were confirmed to be FOSC by multigene phylogenetic analyses based on four genomic loci: β‐tubulin, calmodulin, the second largest subunit of nuclear RNA polymerase II and translation elongation factor 1‐α. There was a high level of genetic diversity among isolates, with multiple phylogenetic lineages detected. Glasshouse bioassays demonstrated that all tested isolates were pathogenic to processing tomato, resulting in significant reductions in plant growth, with above‐ground height reduced by 11%–26% and root dry weight by 44%–83% compared with the control ( p < 0.05). Although aggressiveness varied among isolates, growth reduction occurred irrespective of their phylogenetic placement. Moreover, the shared genetic background of isolates from irrigation water and plant samples highlights the role of irrigation water as a potential source of inoculum in Fusarium epidemics, underscoring its significance for disease management in Australian processing tomato systems.