S14 - Session P5 - Morphological characteristics and pathogenicity of Alternaria and Stemphylium isolates on tomato in vitro

Authors: Lilija Duckena *, Gunita Bimsteine

Tomato is the most commercialized vegetable in Latvia, representing 43.9 % (2020) of the total export volume of fresh vegetables. The tomato plant is susceptible to several diseases caused by fungal pathogens. Until now, no research on tomato diseases has been carried out in Latvia. Early blight (caused by Alternaria spp.) and grey leaf spot (caused by Stemphylium spp.) are commonly observed diseases of tomato. These diseases may affect foliage, stems, and fruits, and they cause significant production and economic losses. Symptoms of diseases are similar, and complex infection is also possible; therefore, precise identification and determination of the pathogenicity of pathogens are necessary. The aim of the research is to compare morphological characteristics of the Alternaria and Stemphylium isolates and determine their pathogenicity on tomato. Samples of leaves and fruits with characteristic symptoms of early blight and grey leaf spot were collected during the 2021 crop season. Isolates of pathogens were obtained by pathogen isolation on potato dextrose agar (PDA). After a week, the colour, type of growth, structure of mycelium and the presence of spores were evaluated. For pathogenicity testing, mycelia plugs (each isolate 5 mm in diameter) were placed in the centre of detached tomato leaves and on unripe and ripe tomato fruits; the pathogenicity was evaluated after seven days. Morphological characteristics of the Alternaria and Stemphylium isolates varied, and further research is required to identify the species of pathogens. Pathogenicity differed depending on the genera of pathogens, particular isolates, and organs of hosts.