Alternaria alternata Causing Disease on Sugar Beet (Beta vulgaris) Steckling in Arizona, USA

Abstract

Sugar beet (Beta vulgaris. L) is an economically important crop which is contributing 55% of the total sugar in the USA. In April 2018, irregular dark brown symptoms were observed in sugar beet stecklings in Arizona where different sugar beet cultivars were grown for seed production (Figure 1). The symptoms covered approximately 5% on the sugar beet root surface. Symptomatic beet root tissue were excised from the junction of diseased and healthy tissue. Small pieces (5mm²) were surface sterilized with 10% sodium hypochlorite for 1min, rinsed thrice with sterile distilled water, air dried and transferred to clarified V8 (CV8), and Potato Dextrose Agar (PDA), and incubated at 24°C with a 12h photoperiod for 5 days. White-dark green velvety colony appeared on both media (Figure 2). Isolates were developed by the single spore isolation technique. Conidia were obclavate or oviod, two to four transverse septa, and pale brown, often in chains (4 to 8 conidia) and or solitary (Figure 3). The dimension of conidia varied from 20.21-40.15 x 7.50-14.12 μm [1- 3]. Based on the morphological characters, the fungus was tentatively identified as Alternaria species. Genomic DNA were extracted via Qiagen kit. A total of 40ng genomic DNA was used to generate a library using NEBNext® Fast DNA Fragmentation & Library Prep Set for Ion TorrentTM for sequencing in Ion TorrentTM Personal Genome MachineTM System.