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POSTERS: New and emerging diseases

First detection of a phytoplasma associated with witches’ broom of industrial hemp in the United States
Jennifer Schoener - Nevada Department of Agriculture. Shouhua Wang- Nevada Dept of Agric

In 2017-2018, industrial hemp (Cannabis sativa) crops in Nye and Humboldt counties exhibited severe stunting and abnormal growth. The percentage of affected plants was approximately 25-30%. The disease was primarily found on “Cherry Wine’ and ‘Berry Blossom’ varieties and symptomatic plants were useless to harvest. Typical symptoms of the disease were excessive apical branching and crowded growth of underdeveloped leaves, giving a shoot proliferation or clusters of witches’ broom appearance. Leaves in a cluster were yellowish, often distorted, and small. These symptoms suggest a phytoplasma infection. DNAs were extracted from 200 mg of leaf midrib and petiole tissue of symptomatic plants. A multiplex real-time PCR assay was performed using phytoplasma-specific primers (JH-F1/JH-F all/JH-R) and probe (JH-P uni). Phytoplasma DNA was detected in 9 of 61 tested samples with Ct values ranging from 14 to 33. Conventional and/or nested PCR was then performed using primer pairs P1/P7 and R16F2n/R2, and PCR amplicons of approximately 1.8 kb (PI/P7) or 1.4kb (nested) were obtained. The PCR products were purified, subcloned into pGEM®-T vector, and sequenced. DNA sequences of 5’- and 3’- ends of PCR amplicons were obtained. BLASTn search suggests that this phytoplasma is closely related to the clover proliferation group, and its identity is currently under study. To our knowledge, this is the first detection of a phytoplasma from industrial hemp crops in the United States.