Interaction of Ditylenchus dipsaci (Kühn, 1857) Filipjev, 1936 (Rhabditida: Anguinidae) and Fusarium proliferatum (Matsush.) Nirenberg ex Gerlach & Nirenberg (Hypocreales: Nectriaceae) on onions

This study aimed to investigate the interaction between Ditylenchus dipsaci (Kühn, 1857) Filipjev, 1936 (Rhabditida: Anguinidae) and Fusarium proliferatum (Matsush.) Nirenberg ex Gerlach & Nirenberg (Hypocreales: Nectriaceae) on two onion cultivars (yellow and purple) under controlled conditions between February and May 2024 in Isparta, Türkiye. The effects of single-pathogen, simultaneous and sequential combined inoculations on disease severity, nematode reproduction and plant growth were evaluated. In the nematode-only treatment (N), the reproduction rate was 9.5 in the yellow onion cultivar and 6.7 in the purple onion cultivar. Nematode reproduction rates in both onion cultivars were reduced in inoculations with both nematodes and fungi. Disease severity in onions treated with F. proliferatum alone was 65%, while it increased to 80-90% with sequential combined inoculations. Plant growth was reduced in all treatments compared to the control. Compared to the D. dipsaci-only treatment, F. proliferatum had a more negative impact on plant development. In yellow onions, the lowest onion wet weight was found in the treatment with F. proliferatum alone, while in purple onions, onion wet weight was similar across F. proliferatum-only, simultaneous and sequential combined inoculations. The results showed that simultaneous and sequential inoculations with F. proliferatum significantly reduced the reproduction of D. dipsaci and increased basal rot severity.