First Record of Geotrichum candidum Causing Root Rot to Sugar beet (Beta vulgaris. L) in Wyoming and Michigan, USA

Abstract

Sugar beet (Beta vulgaris L.) root rotten is caused by a number of soil-borne pathogens included Rhizoctonia solani, Aphanomyces cochlioides, Clonostachys rosea, Globisporangium ultimum, Rhizopus stolonifera, and Fusarium equiseti [1-4]. In September 2019, watersoaked soft rot with brown irregular lesions with a fermented smell, and thick foamy white mycelial growth symptoms were observed on sugar beet roots collected from Wyoming and Michigan (Figure 1 and 2). The symptoms covered approximately 40% of the sugar beet root surface. Diseased beet root tissues were excised from the junction of diseased and healthy tissue. Small pieces (10mm2) were surface sterilized with 10% sodium hypochlorite for 1min, rinsed thrice with sterile distilled water, air-dried on laminar airflow cabinet for 5 minutes, and transferred to corn meal agar (CMA), and clarified V8 (CV8)- incubated at 25°C with a 12-h photoperiod for 7 days. White, thin, flatted, and feathery colonies appeared on both media (Figure 3 and 4). Conidia were arthrosporous, mostly like chains, segmented, hyaline, subglobose, and single-celled (Figure 5). The dimension of conidia varied from 5-12 x 2-5 μm [5]. Based on microscopic and macroscopic characters, the fungus was speculated to be Geotrichum species. Ten isolates were developed by the single spore isolation technique. To confirm the species of the fungus, Genomic DNA was extracted from two representatives of the isolates and the internal transcribed spacer (ITS) region was amplified using the ITS1/ITS4 primers [6]. The amplified PCR products were cleaned and sent for Sanger sequencing by GenScript (GenScript, Piscataway, NJ). A Blastn search of the ITS sequences from the isolates showed 100% identity to those of Geotrichum candidum isolates KF713519.1 and MF782775.1.