Virus-Glomus etunicatum Interactions in Citrus Rootstocks. S. Nemec, U.S. Department of Agriculture, ARS, Orlando, FL 32803. Donald Myhre, Soil Science Department, University of Florida, Gainesville 32611. Plant Dis. 68:311-314. Accepted for publication 15 October 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/PD-68-311.

Sour orange, Citrus macrophylla, and Duncan grapefruit seedlings were blind-bud-inoculated with tristeza virus isolates T-3 and T-1 and citrus leaf rugose virus (CLRV-2), respectively, after growing in a greenhouse for 3 mo in low-phosphorus (P) soil (9–12 μg P/g) amended with Glomus etunicatum or in soil amended with 210 μg P/g only. Controls were virus-free plants grown in these soils. Growth of C. macrophylla and Duncan grapefruit was not significantly reduced by virus infection in the G. etunicatum- or phosphorus-amended soil 98 days after inoculation, but growth of sour orange infected with tristeza virus isolate T-3 was significantly reduced in both soils compared with that in the nonvirus treatments. In growth chamber studies with Duncan grapefruit inoculated with CLRV-2, growth was significantly reduced in both soils compared with the controls because temperatures (27 C day/21 C night and 32 C day/21 C night) were cool enough to favor increased expression of virus symptoms. More root degeneration occurred in virus-inoculated plants in both soils than in controls. In greenhouse studies, fungus chlamydospore numbers and percentage of infection generally were higher in the nonvirus treatments than in virus treatments. Mycorrhizal infection of sour orange did not minimize the pathogenic effects caused by tristeza.