Evaluation of Seed Transmissibility of Soybean Vein Necrosis-Associated Virus in Two Soybean Cultivars Grown Under Field Conditions

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Soybean vein necrosis-associated virus (SVNaV), originally found in Tennessee in 2008, has recently been reported from other soybean-growing regions of the United States as well as Canada. To provide direct evidence for lack of seed transmissibility of SVNaV in soybean, cultivars CF386RR2y/stsn and AG4832 were planted in a field in Kentucky during the 2013 growing season. Typical SVNaV induced symptoms emerged in early August. Tissues were collected from 150 symptomatic and asymptomatic plants of both cultivars and assayed by ELISA. SVNaV was detected in 94% of symptomatic, but none of asymptomatic plants. Seeds were harvested independently from 10 selected infected plants of each cultivar that exhibited the highest ELISA readings. A total of 2085 seeds from both cultivars were planted under greenhouse conditions and subsequently 1955 asymptomatic seedlings were harvested 4-5 weeks post-emergence and assayed individually by ELISA. Sap from only one of the seedlings exhibited an absorbance reading higher than background. However, when all the seeds from the same mother plant were grown and tested, none was positive. This suggests higher than background absorbance value for this single seedling is an anomaly. To search for probable genetic variation among SVNaV isolates from infected mother plants, whose seeds were subjected to grow out test, nucleocapsid protein gene was RT-PCR amplified from 13 mother plants representing both cultivars and sequenced. The analysis of sequences revealed the presence of distinct variants. Lack of potential for SVNaV to be seed transmissible in soybean is discussed.