Disease Note.

Screening Three Cercis Species for Susceptibility to Verticillium dahliae. . K. A. Jacobs, U.S. National Arboretum, 3501 New York Ave. NE, Washington, D.C. 20002-1958. S. E. Bentz, and G. R. Johnson, U.S. National Arboretum, 3501 New York Ave. NE, Washington, D.C. 20002-1958. Plant Dis. 78:09251. Accepted for publication 19 May 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0925C.

Several redbud species (Cercis canadensis L., C. chinensis Bunge, and C. siliquastrum L.) are known to be susceptible to Verticillium wilt, caused by Verticillium albo-atrum Reinke & Berthier and V. dahliae Kleb. (1,2). Variation in response of three Cercis spp. to V. dahliae was examined in 295 seedlings (28 C. canadensis, 177 C. chinensis, and 90 C. yunnanensis Hu & Cheng, an Asian species closely related to C. chinensis) that were grown from seed. At 6 wk, each plant had one-third of its root system severed and inoculated with a conidial suspension (7.5 x 105 spores ml-1 ) for 2 min. The inoculum was derived by mixing spore suspensions obtained from three cultures, each a different isolate of V. dahliae recovered from maple (Acer Saccharum Marsh.), smoke tree (Cotinus sp), or cotton (Gossypium hirsutum L.). Control plants were dipped in water. Transplanted seedlings were rated for symptom development at 1 and 7 mo after inoculation. Symptoms included leaf wilting and necrosis that started at the distal portion of the leaf, and stem vascular streaking. Chlorosis along leaf veins was observed exclusively on the C. canadensis seedlings, and probably resulted from nutrient deficiency. Reisolation of the pathogen was attempted from all symptomatic plants after the 7 mo evaluation. Vascular streaking was present in 100% of symptomatic seedlings, although the pathogen was reisolated from only 67-80% of those seedlings. Significantly more (P = 0.04) C. yunnanensis (36%) and C. chinensis (25%) seedlings developed symptoms and/or died than C. canadensis (7%). This is the first report that interspecific variation in susceptibility to Verticillium wilt exists in redbud, and that C. yunnanensis is susceptible to the disease.