Characterization of Curtoviruses Associated with Curly Top Disease of Tomato in California and Monitoring for These Viruses in Beet Leafhoppers

Abstract

Curly top disease is caused by a complex of curtoviruses (family Geminiviridae), and it continues to plague tomato production in California. To better understand the etiology of curly top of tomatoes in California, polymerase chain reaction (PCR)-based methods were developed and used to characterize the curtoviruses involved, and to monitor for these viruses in the beet leafhopper vector, Circulifer tenellus. From 2002 to 2008, 86 processing and fresh market tomato fields in the Central Valley of California were surveyed for the incidence of curly top symptoms. Representative samples with curly top symptoms were collected from the surveyed fields, as well as from another 24 fields. The incidence of curly top symptoms in most fields ranged from trace (<1%) to low (1 to 5%); however, in 2002, 2003, and 2008, some fields had medium (5 to 20%) or high (>20%) incidences. PCR with general and species-specific primers was used to establish that the predominant species associated with tomato curly top disease were Beet mild curly top virus (BMCTV) and, to a lesser extent, Beet severe curly top virus (BSCTV). The incidence, relative amount, and species of curly top virus in leafhoppers, collected at monthly intervals by the California Department of Food and Agriculture (CDFA) personnel during 2003 to 2008, was also determined. The predominant species detected were BMCTV and BSCTV. The highest incidences of curly top in tomato fields were associated with high populations of leafhoppers (e.g., in 2003 when populations were two times greater than average) having high incidences and levels of curly top virus early in the growing seasons (e.g., March to May 2003 and 2008). Detection of curly top virus in leafhoppers early in the growing season was consistent with acquisition of virus from reservoir hosts in the foothills. However, continued detection of curly top virus in leafhoppers throughout the growing season and development of curly top in late-planted fresh market tomatoes were consistent with the presence of inoculum sources (e.g., weeds or crop plants) in the agricultural areas of the Central Valley. Geographical locations or “hotspots” having higher proportions of curly top virus–positive leafhoppers were identified, which may reveal areas having high concentrations of curly top virus reservoir hosts. The application of these molecular tools has provided new insight into curly top of tomato in California, and may lead to improved curly top management.

Characterization of a New World Monopartite Begomovirus Causing Leaf Curl Disease of Tomato in Ecuador and Peru Reveals a New Direction in Geminivirus Evolution

“…Thus, many of the tomato plants with leaf curl symptoms from Ecuador and Peru were infected with a begomovirus, but the finding that some samples were not infected showed that these symptoms can be caused by other factors (53).…”

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

“…The Svr and Wor strains predominated from the mid-1990s during the first formal survey of the molecular era (Stenger and Ostrow 1996), through subsequent surveys as late as 2008 (Chen et al 2010). In contrast, strain evaluations during the 2013 California outbreak, when upward of $100 million was lost (Gordon 2014), suggest the emergence of new variants displacing the older strains.…”

“…Prior to the 2006-to-2007 collection, the CA/Logan strain was widely perceived to have become very rare and possibly extinct in nature, because no isolates had been identified in many years (Chen et al 2010;Creamer et al 2005). The isolate was believed to exist primarily in laboratory collections.…”

“…Several new species or strains associated with curly top have been identified in various agricultural crops. These are likely the result of recombination among strains and variants during mixed infections, and emerge as significant proportions of the virus population due to selection pressures (Bach and Jeske 2014;Briddon et al 2010;Chen et al 2010Chen et al , 2014Creamer et al 2005;Hernandez and Brown 2010;Hernández-Zepeda et al 2013;Lefeuvre and Moriones 2015;Padidam et al 1999;Razavinejad et al 2013;Stenger 1998;Stenger and McMahon 1997, Stenger and Ostrow 1996, Stenger et al 1990, 1994Strausbaugh et al 2008). In an effort to increase our knowledge of the species and strains currently associated with curly top in sugar beet production in Oregon and Idaho, commercial fields were sampled from 2012 to 2015.…”

Variations of Incidence, Types of Virus Diseases and Insect Vector Populations of Tomato (Solanum lycopersicum L.), Grown in Different Agroecological Regions of Sri Lanka under Two Crop Management Systems

“…Seedlings, transplanted in field, were monitored biweekly and the number of plants showing typical virus disease symptoms was recorded as percentage disease incidence of different types of virus diseases for plants treated with the IMP and the existing management methods. Types of virus diseases and disease incidence were identified based on the typical symptoms shown by respective virus diseases according to disease diagnosis manuals and descriptions of previous studies (Whitfield et al, 2005;Chen et al, 2010;Samarakoon et al, 2012). The tomato plants remained as asymptomatic at the time of observation were designated as healthy plants.…”