Aphid Vectors and Grass Hosts of Barley Yellow Dwarf Virus and Cereal Yellow Dwarf Virus in Alabama and Western Florida
Type of Degreedissertation
Entomology and Plant Pathology
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Yellow Dwarf (YD) is a major disease problem of wheat in Alabama and is estimated to cause yield loss of 21-42 bushels per acre. The disease is caused by a complex of luteoviruses comprising two species and several strains, including Barley yellow dwarf virus (BYDV), strain PAV, and Cereal yellow dwarf virus (CYDV), strain RPV. The viruses are exclusively transmitted by aphids. Suction trap data collected between 1996 and 1999 in North Alabama recorded the presence of several species of aphids that are known to be B/CYDV vectors. Aphids were surveyed in the beginning of planting seasons in several wheat plots throughout Alabama and western Florida for four consecutive years. Collected aphids were identified and bioassayed for their B/CYDV-infectivity. This survey program was designed to identify the aphid (Hemiptera: Aphididae) species that serve as fall vectors of B/CYDV into wheat planting. From 2005 to 2008, bird cherry-oat aphid, Rhopalosiphum padi (L.), rice root aphid, Rhopalosiphum rufiabdominale (Sasaki), and greenbug, Schizaphis graminum (Rondani), were consistently found between October and December. The species of aphids and their timing of appearance in wheat plots were consistent with flight data collected in North Alabama between 1996 and 1999. Both R. padi and R. rufiabdominale were found to carry and transmit BYDV-PAV and CYDV-RPV. Low overall numbers of collected aphids and low proportion of infective aphid made it difficult to conclusively identify the primary vector of B/CYDV in Alabama. The source of summer/fall infection of BYDV and CYDV is not known in Alabama. Pasture grasses may provide a means of survival during summer months when wheat is not available in Alabama. Variety plots of three pasture grasses were sampled in summer between 2007 and 2009 for B/CYDV and aphids. Of the three pasture grasses surveyed, bahiagrass was found to consistently harbor BYDV-PAV and CYDV-RPV, while limpograss was found to harbor BYDV-PAV and CYDV-RPV irregularly. This is the first report of BYDV on bahiagrass and limpograss. No aphids were found during this study on limpograss and gamagrass while the aphid Sipha flava (Forbes) was found in two out of three years of survey on bahiagrass.