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

Garlic (<i>Allium sativum</i> L.), a vital global crop, suffers significant losses from soil-borne fungal pathogens such as <i>Fusarium proliferatum</i>, responsible for <i>Fusarium</i> bulb rot, and <i>Stromatinia cepivora</i>, the causal agent of white rot. In May 2023, garlic fields near Makó City, Hungary, showed simultaneous yellowing and wilting symptoms of unknown fungal infestations, which appeared sporadically. The causal pathogens were later confirmed as <i>F. proliferatum</i> and <i>S. cepivora</i> 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 <i>in vitro</i> and <i>in planta</i> tests. Dual culture assays of <i>F. proliferatum</i> and <i>S. cepivora</i> 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 <i>F. proliferatum</i> and 6.40% for <i>S. cepivora</i>, 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 ‘Aulxito’, ‘Sabadrome’, ‘Arno’, ‘Garcua’, and ‘Makói Tavaszi’ were highly susceptible to both pathogens, while ‘Flavor’ and ‘Sabagold’ exhibited only mild symptoms when inoculated with <i>F. proliferatum</i> and <i>S. cepivora</i>, respectively. Simultaneous inoculation resulted in more rapid and severe infections, exhibiting disease incidences above 96.00% across all cultivars. Remarkably, the cultivar ‘Elephant’ exhibited complete resistance to both pathogens, even under simultaneous inoculation, highlighting its potential for future garlic resistance breeding programs.