Fusarium basal rot disease (FBR) is considered a serious threat to commercial onion production in Israel and worldwide. Today, coping means applied in Israel against the disease have limited efficiency and include a four-year crop cycle and disinfecting the soil with metam sodium. At the same time, agricultural tools (harrows, plows, etc.), contaminated equipment and workers facilitate spread of the disease to new growth areas, and the field disease incidence in Israel now reaches 8% of yields in heavily infected areas. Infected onions do not always show disease symptoms and the problem worsens if they arrive at storage facilities, especially since this pathogen genus produces known toxins. The current study aims at examining the potential of chemical control to reduce the damage caused by this disease. To this end, nine commercial fungicides were scanned in plate sensitivity assay against the main pathogens involved, Fusarium oxysporum f. sp. cepae and Fusarium acutatum. Several fungicides were found to be highly effective against the two pathogens, especially the mixtures Azoxystrobin + Difenoconazole, Fluopyram + Trifloxystrobin, or the Fluazinam compounds. Three selected preparations previously tested in seedlings were evaluated here in a full growing season. Prochloraz successfully protected the Orlando variety (white onion, Riverside cv.) and the Noam variety (red onion) at all growth stages against F. oxysporum f. sp. cepae. At the same time, this treatment was ineffective against F. acutatum in Noam cv. Another anti-fungal preparation, Fludioxonil + Sedaxen mixture, showed a wider range of effectiveness at the season’s end against the two Fusarium species tested in both onion cultivars. These results are an important step towards developing FBR control in commercial onion fields. Follow-up work is needed to optimize the pesticides’ concentrations and their application methods and to test them on a field scale. Interestingly, these pathogens were more aggressive towards the cultivar from which they were isolated: F. oxysporum f. sp. cepae to the red onion Noam cv. and F. acutatum to the white Orlando cv. Infecting the plants with both pathogens reduced disease symptoms in the white Orlando cv, suggesting antagonistic interactions in this onion genotype.

Fusarium basal rot (FBR) is a significant limitation to Allium production worldwide. The damage of the disease can be observed throughout the entire crop cycle. The current research aimed to understand better the FBR affecting onion (Allium cepa) in northeast Israel by assessing the disease incidences. It also focuses on studying the Fusarium population structure involved in the disease outburst in two representative fields, one in the Galilee (Hula Valley) and the second in the Golan Heights. Using colony morphology, microscopic taxonomic keys, and molecular methods, a new, unreported Fusarium solani species was discovered as a wildly spread member of the Fusarium pathobiome community. This species appeared to be more generalist in its nature since it was found in all three onion cultivars’ samples. It was also less virulent than the other two species identified. While the Galilee yellow Orlando onion cultivar is colonized by F. solani and two other, less abundant species, F. oxysporum f. sp. cepae, and F. acutatum, the Golan Heights Fusarium community, show host specificity. In the Golan Heights fields, F. oxysporum f. sp. cepae inhabited the red 505 onion cultivar, whereas F. acutatum colonized the yellow 100 cultivar. A better understanding of this disease complexity caused by different Fusarium species with a divergence in host susceptibility and virulence is critical for developing disease management strategies. Since each Fusarium species reacts differently to pest control treatments, the changes in the species composition may require specifically adapted pest control solutions.