Verticillium Wilt Resistance in Pistachio Rootstock Cultivars: Assays and an Assessment of Two Interspecific Hybrids. D. P. Morgan, Department of Plant Pathology, University of California, Berkeley 94720. L. Epstein, and L. Ferguson. Department of Plant Pathology, University of California, Berkeley 94720, and Kearney Agricultural Center, Parlier, CA 93648. Plant Dis. 76:310-313. Accepted for publication 25 October 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0310.

Pistacia integerrima (rootstock cultivar Pioneer Gold) is resistant to Verticillium dahliae, and P. atlantica (rootstock cultivar Standard Atlantica) is susceptible in the field. We developed greenhouse and laboratory assays that differentiate between the resistant and the susceptible cultivars. After injection of the stems of seedlings with conidia, the cultivars showed differential symptoms. After infusion of conidia into stems, V. dahliae colonized significantly fewer xylem vessels in the resistant than in the susceptible cultivar. We used the assays and a field test to assess Verticillium wilt resistance in two interspecific hybrid pistachio rootstock cultivars, Pioneer Gold II (PGII) and University of California at Berkeley I (UCBI). We conclude that UCBI is moderately resistant to resistant and that PGII is moderately susceptible to susceptible in comparison with Pioneer Gold and Standard Atlantica.