Colonization of sunflower seed with Alternaria alternata

Abstract

Sunflower (Helianthus annuus L.) is one of the most important oilseed crops throughout the world, and in Serbia it is grown on about 160,000 to 210,000 ha. Alternaria alternata (Fr.) Keissler has been detected as the most frequent seed-borne pathogen, able to infect a wide variety of plant species in different countries. During a routine seed quality control and seed health testing analysis of sunflower seed in 2018-2019, according to ISTA Rules, Alternaria spp. infection was observed on an average of 18%. The aim of this study was the isolation and identification of Alternaria spp. based on their morphological characteristics and molecular analyses. Isolation of the pathogen was carried out by transferring infected seeds onto a potato dextrose agar (PDA), and subsequent incubation at 25°C. Seven days later, 21 isolates formed circular, smooth, grey to brownish-black colonies, with concentric zones of very intensive sporulation. Conidiophores were branched, solitary or in small groups, brown to olivaceous brown, ranging from 128 to 232 µm. All isolates were subcultured onto a PDA using a single spore technique.