Co-Occurrence of Stromatinia cepivora and Fusarium proliferatum Fungi on Garlic: In Vitro Investigation of Pathogen–Pathogen Interactions and In Planta Screening for Resistance of Garlic Cultivars

Garlic (Allium sativum L.), a vital global crop, suffers significant losses from soil-borne fungal pathogens such as Fusarium proliferatum, responsible for Fusarium bulb rot, and Stromatinia cepivora, the causal agent of white rot. In May 2023, garlic fields near Mak&oacute: City, Hungary, showed simultaneous yellowing and wilting symptoms of unknown fungal infestations, which appeared sporadically. The causal pathogens were later confirmed as F. proliferatum and S. cepivora through sampling of symptomatic garlic plants, incubation in humid chambers to stimulate fungal growth, and culturing on Potato Dextrose Agar (PDA) under sterile conditions. This was followed by hyphal tip isolation and purification. Molecular identification was performed using ITS1-2 sequencing, supported with morphological identification based on colony and microscopic features. This research aimed to elucidate pathogen interaction dynamics and assess the resistance of eleven garlic cultivars to both single and simultaneous inoculations by these pathogens, under in vitro and in planta tests. Dual culture assays of F. proliferatum and S. cepivora were studied at two time points: Day 8, marking the cessation of growth along the interacting fronts due to competitive coexistence, and Day 14, when single cultures reached full radial growth. On Day 8, inhibition percentages were 8.47% for F. proliferatum and 6.40% for S. cepivora, reflecting the initial effects of competitive interactions at the point of contact. By Day 14, inhibition rates increased to 25.39% and 28.61%, respectively, highlighting the cumulative effects of sustained competition and the growing difference between single and dual culture growth. Inoculation trials, involving placing fungal disks onto the basal areas of wounded garlic cloves, revealed considerable variability in disease incidence and severity. Cultivars such as &lsquo:Aulxito&rsquo:, &lsquo:Sabadrome&rsquo:, &lsquo:Arno&rsquo:, &lsquo:Garcua&rsquo:, and &lsquo:Mak&oacute:i Tavaszi&rsquo: were highly susceptible to both pathogens, while &lsquo:Flavor&rsquo: and &lsquo:Sabagold&rsquo: exhibited only mild symptoms when inoculated with F. proliferatum and S. cepivora, respectively. Simultaneous inoculation resulted in more rapid and severe infections, exhibiting disease incidences above 96.00% across all cultivars. Remarkably, the cultivar &lsquo:Elephant&rsquo: exhibited complete resistance to both pathogens, even under simultaneous inoculation, highlighting its potential for future garlic resistance breeding programs.