Lasiodiplodia theobromae disease symptom development in young avocado (Persea americana L.) plants depends on the inoculation method

Abstract Lasiodiplodia theobromae is a pathogenic fungus of more than 500 plant species, including avocado ( Persea americana Mill.). The global production volume of avocado exceeded 911,000 metric tons in 2023. Although detailed quantitative surveys of yield losses caused by L. theobromae are not available for most avocado-producing regions, estimates indicate that this pathogen is associated with stem-end rot disease in 30-35% of plots located in the Department of Antioquia in Colombia (Ramírez-Gil et al. Heliyon 7: e05905, 2021), suggesting an enormous economic impact. As yield losses strongly depend on the virulence of isolates, a reliable method for determining their aggressiveness is indispensable for initiating disease control measures. In this study, we compared progression of external and internal necrosis caused by the aggressive L. theobromae isolate LA-VLCA3 inoculated into wounded middle parts of the stem and onto excised apices. Irrespective of the inoculation method, internal progression of necrosis preceded that of external necrosis. Spreading of external and internal necrosis was significantly more severe in plants inoculated at the apex than in mid-stem inoculated plants. We conclude that apex inoculation causes stronger symptoms and is therefore better suited to compare virulence of isolates than mid-stem inoculation.