Beet curly top virus Strains Associated with Sugar Beet in Idaho, Oregon, and a Western U.S. Collection

Abstract

Curly top of sugar beet is a serious, yield-limiting disease in semiarid production areas caused by Beet curly top virus (BCTV) and transmitted by the beet leafhopper. One of the primary means of control for BCTV in sugar beet is host resistance but effectiveness of resistance can vary among BCTV strains. Strain prevalence among BCTV populations was last investigated in Idaho and Oregon during a 2006-to-2007 collection but changes in disease severity suggested a need for reevaluation. Therefore, 406 leaf samples symptomatic for curly top were collected from sugar beet plants in commercial sugar beet fields in Idaho and Oregon from 2012 to 2015. DNA was isolated and BCTV strain composition was investigated based on polymerase chain reaction assays with strain-specific primers for the Severe (Svr) and California/Logan (CA/ Logan) strains and primers that amplified a group of Worland (Wor)-like strains. The BCTV strain distribution averaged 2% Svr, 30% CA/ Logan, and 87% Wor-like (16% had mixed infections), which differed from the previously published 2006-to-2007 collection (87% Svr, 7% CA/Logan, and 60% Wor-like; 59% mixed infections) based on a contingency test (P < 0.0001). Whole-genome sequencing (GenBank accessions KT276895 to KT276920 and KX867015 to KX867057) with overlapping primers found that the Wor-like strains included Wor, Colorado and a previously undescribed strain designated Kimberly1. Results confirm a shift from Svr being one of the dominant BCTV strains in commercial sugar beet fields in 2006 to 2007 to becoming undetectable at times during recent years.Beet curly top virus (BCTV) in sugar beet (Beta vulgaris L.) is an important yield-limiting disease problem in semiarid production areas of the western United States and in Middle Eastern countries (Bennett 1971;Gharouni Kardani et al. 2013;Harveson 2015;Stenger and McMahon 1997;Strausbaugh et al. 2008;Yazdi et al. 2008). BCTV is transmitted in a persistent circulative manner by the beet leafhopper, Circulifer tenellus Baker (Hemiptera: Cicadellidae), and can infect over 300 dicotyledonous plant species (Bennett 1971). Yield may be affected in important crops such as common bean, pepper, spinach, sugar beet, and tomato (Blickenstaff and Traveller 1979;Chen and Gilbertson 2009;Creamer et al. 1996;Soto and Gilbertson 2003;Soto et al. 2005). Several distinct, genetically characterized members of the genus Curtovirus have been confirmed as causative agents of curly top in sugar beet (Briddon et al. 1998;Gharouni Kardani et al. 2013;Heydarnejad et al. 2007Heydarnejad et al. , 2013Soleimani et al. 2013;Stenger 1998;Strausbaugh et al. 2008;Yazdi et al. 2008). However, reevaluation of the genus Curtovirus assigned most of these viruses formerly recognized as distinct Curtovirus spp. as strains of BCTV (Varsani et al. 2014a).Curtovirus isolates and strains with greater than 94% sequence identity are now considered variants of the same strain and those with 77% or less sequence identity are considered different species (Varsani et al. 2014a). There...

First Insights Into the Virus and Viroid Communities in Hemp (Cannabis sativa)

“…To detect BCTV in hemp leaf tissues and leafhoppers, samples were analyzed by PCR using universal BCTV primers BCTV2-F and BCTV2-R that amplify a 496-bp fragment of the coat protein (CP), a region that is conserved among BCTV strains (Strausbaugh et al, 2017) with GoTaq R Flexi DNA polymerase (Promega, Madison, WI). The amplification cycle consisted of 94 • C initial denature for 5 min, 25 cycles of denaturation at 94 • C for 1 min, 58 • C annealing for 2 min, and 72 • C extension for 2 min, followed by a 10-min final extension.…”

“…The virus is transmitted only by the leafhopper, Circulifer tenellus Baker (Hemiptera: Cicadellidae) in a circulative propagative manner (Bennett, 1971) (reviewed in Chen and Gilbertson, 2016). There are 11 strains of BCTV [California/Logan (CA/Logan), Colorado (CO), Kimberly1 (Kim1), Leafhopper 71 (LH71), Mild (Mld), Pepper curly top (PeCT), Pepper yellow dwarf (PeYD), Severe (Svr), Severe pepper (SvrPep), Spinach curly top (SpCT), and Worland (Wor)] and recent isolates sequenced from sugar beet and tomato added the Kim1 and LH71 strains (reviewed in Chen and Gilbertson, 2016;Strausbaugh et al, 2017). The occurrence of the various strains of BCTV varies over time by geographic region and are often observed as co-infections (Strausbaugh et al, 2017;Creamer, 2020).…”

Pest categorisation of Beet curly top virus (non‐EU isolates)

“…Recently, BCTV genome sequences from US virus collections of sugar beet and other crops were evaluated to elucidate the current prevalence of particular strains, to identify strain shifts and to discover the emergence of new virus variants (Strausbaugh et al., ). Following the recently accepted BCTV nomenclature, two additional BCTV sequence clades (Strausbaugh et al., ) were identified, demonstrating the existence of two additional strains of BCTV (BCTV‐Kimberly and BCTV‐Leafhopper71). There are now altogether 11 BCTV strains identified (Table ).…”

“…Most impact from BCTV is reported from outbreaks in sugar beet and tomato and from a range of other crops, including pepper and basil (Wisler and Duffus, 2000;Strausbaugh et al, 2008Strausbaugh et al, , 2017Chen et al, 2010Chen et al, , 2014. BCTV is most prevalent in the USA where already in 1890, the curly top disease was recognised as a serious threat to the sugar beet production and almost destroyed the California sugar beet industry (Wisler and Duffus, 2000).…”

“…Recently, BCTV genome sequences from US virus collections of sugar beet and other crops were evaluated to elucidate the current prevalence of particular strains, to identify strain shifts and to discover the emergence of new virus variants (Strausbaugh et al, 2017). Following the recently Is the identity of the pest established?…”