Creation of tomato source material with resistance to Alternaria and a complex of economically valuable traits for the development of varieties in the conditions of the Primorsky Krai of the Far East

Relevance. The infection of Solanum lycopersicum L. by Alternaria, caused by micromycetes of the genus Alternaria, is consistently harmful in the monsoon climate of Primorsky Krai. Seasons with abnormally high rainfall levels trigger the development of epiphytotics, resulting in annual crop losses exceeding 30 % and reaching 80 % in susceptible varieties and hybrids. Due to climate change and the increasing aggressiveness of new pathogen races, the search for sources of resistance for breeding remains relevant. The purpose. of this work is to create and evaluate a new source material that is adapted to a high back-ground of Alternaria infection and has a different combination of other selection traits. Material and Methods. The work was carried out in 2020–2025 on the experimental field of the Primorskaya Vegetable Experimental Station – a branch of the Federal Scientific Vegetable Center on meadow-brown soils with a heavy mechanical composition. 23 tomato lines were studied, obtained by successive selections from the splitting offspring of F2-4 hybrid combinations of Ottawa 30 (line L8) with parental determinate lines (L3-L7), created on the basis of the best varieties of breeding of FSBSI FSVC, combining the variety in the mass, shape and color of the fruit. The cultivation technology is the generally accepted for Primorsky Krai. During the vegetation period, phenological observations, phytopathological assessment of the records of the manifestation of target features were carried out. Results. Testing of the created tomato lines allowed to differentiate them by breeding value as a source material for different directions of breeding. Five lines were selected as a promising source material for breeding for resistance to alternaria: GK-68/20/26, GK-87/13/14, GK-48/1/1,GK-48/1/2 and GK-85/3/3. The GK-85/3/1, GK-86/1/1, and GK-87/1/1 lines can serve as sources of a combination of traits such as productivity, large fruit size, and high fruit quality. The introduction of this new material into breeding practices will allow for the creation of competitive varieties and hybrids that are resistant to Alternaria, minimizing the dependence of agricultural technologies on repeated chemical treatments, reducing product losses, and ensuring sustainable production of tomatoes that meet market requirements for both productivity and nutritional value.