Prevention and Control of Fusarium spp., the Causal Agents of Onion (Allium cepa) Basal Rot

Abstract

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.

Molecular Real-Time PCR Monitoring of Onion Fusarium Basal Rot Chemical Control

“…Yet, FBR can occur at any stage of the crop cycle. The results of pre- and post-harvest FBR are significant decreases in crop yield, primarily attributed to reduced bulb size (growth suppression), bulb decay, and a reduction in the shelf life of onions [ 3 ]. Depending on the field’s infection severity and the cultivar’s susceptibility degree, yield losses can reach from 39% (in Turkey [ 4 ]) to 50% (in Nigeria [ 5 ] and India [ 6 ]).…”

Fusarium population dynamics in commercial onion fields in Northeastern Israel

“…The current study's ndings are economically signi cant since each Fusarium species may react differently to control treatments [9]. Thus, knowing the exact population structure may assist in tailoring an FBR protection to maximize its e ciency.…”

Biological Control of Fusarium oxysporum, the Causal Agent of Fusarium Basal Rot in Onion by Bacillus spp.

“…FBR is sometimes called damping-off in onion seedlings because the disease causes pre- and post-emergence damping-off in the early stages of onion plant development ( Degani et al, 2022 ; Kintega et al, 2020 ; Le et al, 2021 ; Shin et al, 2023 ). Infected seedlings at the early stage, especially at transplantation, die or were severely stunted, but the symptoms were reduced or did not appear when infection occurs at later stages ( Retig et al, 1970 ; Stadnik and Dhingra, 1997 ).…”