Bacterial wilt symptoms are impacted by host age and involve net downward movement of Erwinia tracheiphila in muskmelon

Cucurbit bacterial wilt, caused by Erwinia tracheiphila, is a damaging disease of cucurbit crops in the Midwest and Northeast U.S. Current management of bacterial wilt relies primarily on insecticide applications to control striped and spotted cucumber beetles (Acalymma vittatum and Diabrotica undecimpunctata howardi, respectively), which vector E. tracheiphila. Development of alternative management strategies is constrained by a lack of understanding of bacterial wilt etiology. The impact of host age on rate on symptom development and extent of bacterial movement in the xylem of muskmelon (Cucumis melo cv. Athena) was evaluated following wound inoculation of 2- to 8-week-old plants in growth chamber experiments. Wilting occurred more rapidly in plants after inoculating E. tracheiphila into 2- or 4-week-old plants than 6- or 8-week-old plants. Recovery of viable cells from stem segments revealed that vascular spread of E. tracheiphila was more extensive below than above the inoculation point. These findings provide experimental evidence that host age impacts the rate of symptom development in cucurbit bacterial wilt and that movement of the xylem-inhabiting pathogen E. tracheiphila within muskmelon plants occurs primarily in the downward direction

Bacterial wilt symptoms are impacted by host age and involve net downward movement of Erwinia tracheiphila in muskmelon

Cucurbit bacterial wilt, caused by Erwinia tracheiphila, is a damaging disease of cucurbit crops in the Midwest and Northeast U.S. Current management of bacterial wilt relies primarily on insecticide applications to control striped and spotted cucumber beetles (Acalymma vittatum and Diabrotica undecimpunctata howardi, respectively), which vector E. tracheiphila. Development of alternative management strategies is constrained by a lack of understanding of bacterial wilt etiology. The impact of host age on rate on symptom development and extent of bacterial movement in the xylem of muskmelon (Cucumis melo cv. Athena) was evaluated following wound inoculation of 2- to 8-week-old plants in growth chamber experiments. Wilting occurred more rapidly in plants after inoculating E. tracheiphila into 2- or 4-week-old plants than 6- or 8-week-old plants. Recovery of viable cells from stem segments revealed that vascular spread of E. tracheiphila was more extensive below than above the inoculation point. These findings provide experimental evidence that host age impacts the rate of symptom development in cucurbit bacterial wilt and that movement of the xylem-inhabiting pathogen E. tracheiphila within muskmelon plants occurs primarily in the downward direction.This is a manuscript of an article published as Liu, Q., G.A. Beattie, E. Saalau Rojas and M.L. Gleason. 2018. Bacterial wilt symptoms are impacted by host age and involve net downward movement of Erwinia tracheiphila in muskmelon. European Journal of Plant Pathology 151:803-810. doi: 10.1007/s10658-018- 1418-7. Posted with permission.</p

First Report of Soybean Vein Necrosis Disease Caused by Soybean vein necrosis-associated virus in Wisconsin and Iowa

Several viral diseases of soybean (Glycine max) have been identified in the north-central U.S. soybean production area, which includes Wisconsin and Iowa (2). Previously, Soybean vein necrosis disease (SVND) caused by Soybean vein necrosis-associated virus was reported in Arkansas, Tennessee, and other southern states (4). In September 2012, soybean plants with symptoms similar to those reported for SVND (4) were observed in fields across Wisconsin and Iowa. Symptoms included leaf-vein and leaf chlorosis, followed by necrosis of the leaf veins and eventually necrosis of the entire leaf. Six samples with symptoms indicative of SVNaV were collected from research plots located at the West Madison Agricultural Research Station located in Madison, WI. An additional three samples were collected from three locations in central Iowa. Total RNA extracted from each sample using the Trizol Plus RNA purification kit (Invitrogen, Carlsbad, CA) was used to generate complementary DNA (cDNA) using the iScript cDNA synthesis kit (Bio-Rad Laboratories, Hercules, CA) following the manufacturers\u27 suggested protocols. The resulting cDNA was used as template in a PCR with SVNaV-specific primers, SVNaV-f1 and SVNaV-r1 (3). PCRs of two of the six Wisconsin samples and two Iowa samples were positive. Amplification products were not detected in the other five samples. The amplification products from the four strongly positive samples were purified using the Wizard SV Gel and PCR Purification Kit (Promega, Madison, WI) following the manufacturer\u27s suggested protocol and were subjected to automated sequencing (University of Wisconsin Biotechnology Center or Iowa State University, DNA Sequencing Facilities). BLASTn (1) alignments of the 915-bp consensus sequence revealed 98% and \u3e99% identity of the Wisconsin and Iowa samples, respectively, with the ‘S’ segment of the SVNaV ‘TN’ isolate (GenBank Accession No. GU722319.1). Samples from the same leaf tissue used above, were subjected to serological tests for SVNaV using antigen coated-indirect ELISA (3). Asymptomatic soybeans grown in the greenhouse were used as a source of leaves for negative controls. These tests confirmed the presence of SVNaV in eight symptomatic soybean leaflets collected in Wisconsin and Iowa. The asymptomatic control and one Iowa sample, which was also PCR-negative, were also negative by serological testing. Six additional samples from soybean fields in as many Wisconsin counties (Fond Du Lac, Grant, Green, Juneau, Richland, Rock) tested positive for SVNaV using specific primers that amplify the ‘L’ segment (4). The sequenced amplification products (297-bp) showed 99 to 100% homology to the L segment of the TN isolate (GU722317.1). To our knowledge, this is the first report of SVNaV associated with soybean and the first report of SVND in Wisconsin and Iowa. Considering that little is known about SVNaV, it is assumed that it is like other Tospoviruses and can cause significant yield loss (4). Soybean is a major cash crop for Wisconsin and Iowa, and infection by SVNaV could result in potential yield loss in years where epidemics begin early and at a high initial inoculum level

First Report of Soybean Vein Necrosis Disease Caused by Soybean vein necrosis-associated virus in Wisconsin and Iowa

Several viral diseases of soybean (Glycine max) have been identified in the north-central U.S. soybean production area, which includes Wisconsin and Iowa (2). Previously, Soybean vein necrosis disease (SVND) caused by Soybean vein necrosis-associated virus was reported in Arkansas, Tennessee, and other southern states (4). In September 2012, soybean plants with symptoms similar to those reported for SVND (4) were observed in fields across Wisconsin and Iowa. Symptoms included leaf-vein and leaf chlorosis, followed by necrosis of the leaf veins and eventually necrosis of the entire leaf. Six samples with symptoms indicative of SVNaV were collected from research plots located at the West Madison Agricultural Research Station located in Madison, WI. An additional three samples were collected from three locations in central Iowa. Total RNA extracted from each sample using the Trizol Plus RNA purification kit (Invitrogen, Carlsbad, CA) was used to generate complementary DNA (cDNA) using the iScript cDNA synthesis kit (Bio-Rad Laboratories, Hercules, CA) following the manufacturers' suggested protocols. The resulting cDNA was used as template in a PCR with SVNaV-specific primers, SVNaV-f1 and SVNaV-r1 (3). PCRs of two of the six Wisconsin samples and two Iowa samples were positive. Amplification products were not detected in the other five samples. The amplification products from the four strongly positive samples were purified using the Wizard SV Gel and PCR Purification Kit (Promega, Madison, WI) following the manufacturer's suggested protocol and were subjected to automated sequencing (University of Wisconsin Biotechnology Center or Iowa State University, DNA Sequencing Facilities). BLASTn (1) alignments of the 915-bp consensus sequence revealed 98% and >99% identity of the Wisconsin and Iowa samples, respectively, with the ‘S’ segment of the SVNaV ‘TN’ isolate (GenBank Accession No. GU722319.1). Samples from the same leaf tissue used above, were subjected to serological tests for SVNaV using antigen coated-indirect ELISA (3). Asymptomatic soybeans grown in the greenhouse were used as a source of leaves for negative controls. These tests confirmed the presence of SVNaV in eight symptomatic soybean leaflets collected in Wisconsin and Iowa. The asymptomatic control and one Iowa sample, which was also PCR-negative, were also negative by serological testing. Six additional samples from soybean fields in as many Wisconsin counties (Fond Du Lac, Grant, Green, Juneau, Richland, Rock) tested positive for SVNaV using specific primers that amplify the ‘L’ segment (4). The sequenced amplification products (297-bp) showed 99 to 100% homology to the L segment of the TN isolate (GU722317.1). To our knowledge, this is the first report of SVNaV associated with soybean and the first report of SVND in Wisconsin and Iowa. Considering that little is known about SVNaV, it is assumed that it is like other Tospoviruses and can cause significant yield loss (4). Soybean is a major cash crop for Wisconsin and Iowa, and infection by SVNaV could result in potential yield loss in years where epidemics begin early and at a high initial inoculum level.This abstract is from Plant Disease 97 (2013): 693, doi:10.1094/PDIS-11-12-1096-PDN. Posted with permission.</p