Effect of limestone on development of Verticillium wilt of spinach
W. YANG (1), A. Iglesia-Garcia (1), L. du Toit (2), B. Bluhm (1), J. Correll (1)
(1) University of Arkansas, Fayetteville, AR, U.S.A.; (2) Mount Vernon, WA, U.S.A.
Phytopathology 100:S142

Verticillium wilt, caused by Verticillium dahliae, is an important vascular wilt disease of many agricultural crops and, more recently, has become problematic for spinach seed production. Development of Verticillium wilt is influenced by soil conditions such as pH, moisture, and temperature. In an effort to optimize greenhouse pathogenicity and virulence tests, the effect of limestone (5 g/L CaCO3) on the development, incidence, and severity of Verticillium wilt symptoms on spinach was evaluated. In addition, the infection process was monitored using wild-type isolates and genetically marked strains in the form of nitrate non-utilizing (nit) mutants. Limestone and no limestone treatments were evaluated and compared to a non-limed control treatment. Treatments consisted of amending potting mix with different rates of limestone application, or drenching the potting medium with a limestone solution. Potting mix pH was recorded before and after each experiment. Plants were inoculated by adding V. dahliae spores to the root plug and monitoring disease development. Both wild-type isolates and nit mutants caused symptoms of Verticillium wilt, and both types of isolates were recovered from inoculated plants. Limestone treatments caused a significant increase in disease severity of Verticillium wilt of spinach.