Identification and Characterization of Alternaria Species Causing Early Blight on Tomato in Kazakhstan

Abstract

Early blight, caused by fungi of the genus Alternaria, is one of the most destructive diseases affecting tomato plants, leading to a decrease in yield and commercial value. Studies so far on Alternaria spp. affecting tomato in Kazakhstan have been limited to morphological identification or molecular analysis, without an in-depth phylogenetic study and pathogenicity assessment. In this study, between 2023 and 2024, 61 isolates were obtained from tomato leaves with early blight symptoms and identified, based on conidial morphology and DNA sequencing, as A. tenuissima (54%) and A. alternata (46%). The pathogenicity assessment showed that the disease index for A. tenuissima was 21.7–53.3, while it was 41.7–60.0 for A. alternata, indicating greater aggressiveness of the latter species. The disease index varied by region, with the highest average value recorded for A. alternata from Almaty (55.7%), while 38.2% and 36.2% for A. tenuissima were recorded from Pavlodar and Akmola, respectively. Both species showed notable intraspecific variation in pathogenicity. To our knowledge, this is the first reported case of A. tenuissima detection as the causative agent of early blight in tomato plants in Kazakhstan. The results of this study may help facilitate the development of effective disease management strategies.