Creation and characterization of tomato hybrid populations as source material for genomic mapping of resistance to early blight

Abstract

Background and Aim. Early blight, caused by fungi of the genus Alternaria, is one of the most economically significant diseases of tomato and leads to substantial yield losses. Improving the efficiency of breeding for resistance requires the creation of hybrid material and the formation of experimental populations suitable for subsequent genomic analysis. The aim of this study was to obtain tomato hybrid
combinations, evaluate their phenotypic traits, and select plants contrasting in resistance for further whole-genome analysis using the BSA-seq method.
Materials and Methods. The research was conducted in 2023-2025 at the Laboratory of Plant Biotechnology and Breeding of the National Center for Biotechnology and at the field station of the Regional Branch "Kainar” of the Kazakh Research Institute of Fruit and Vegetable Growing. The study involved four tomato genotypes characterized by contrasting levels of resistance: moderately susceptible
- Samaladai, Kitai-12×Moya radost'; and highly resistant - Venera×Mechta, Gloriya×BSS-335.
Hybridization was performed using parental forms differing in resistance.
Results. Cross efficiency varied among combinations: the most productive was Venera×Mechta*Samaladai (60%), while Gloriya×BSS-335*Samaladai and Gloriya×BSS-335*Kitai-12×Moya radost' showed 10% and 20%, respectively. Phenological observations showed that F2 hybrids exhibited reduced “emergence-flowering” and “flowering-ripening” periods compared to parental forms,
with Venera×Mechta*Samaladai being the earliest maturing (105 days). The hybrids showed variability
in morphological traits: plant height ranged from 48.6 to 55.7 cm (comparable to parents), and canopy diameter reached up to 53.8 cm in some combinations. Leaf number in hybrids was lower (13.8-14.7) compared with parental forms (20.3-25.0). In terms of productivity, the combination Gloriya×BSS-335*Kitai-12×Moya radost' was the most notable, forming 9.6 fruits per plant and exceeding the parental genotypes. Phenotypic assessment of early blight resistance revealed wide variability in F2 (0-5 points),
confirming the polygenic nature of inheritance. Resistant and susceptible F2 bulks were formed for subsequent whole-genome sequencing using the BSA-seq approach.
Conclusion. The results obtained enabled the formation of three hybrid populations intended for further whole genome analysis using BSA-seq. The study provides a foundation for identifying genetic loci associated with early blight resistance and for their future application in tomato breeding.