An In Vitro Assay to Evaluate Sources of Resistance in Asparagus spp. to Fusarium Crown and Root Rot. Christine T. Stephens, Associate Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Wade H. Elmer, Research Associate, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Plant Dis. 72:334-337. Accepted for publication 4 November 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0334.

Asparagus spp. grown aseptically in test tubes containing Hoagland’s solution and agar were inoculated with spore suspensions of pathogenic isolates of Fusarium oxysporum f. sp. asparagi or F. moniliforme. Disease severity was assessed after 3 wk, using a scale based on percentage of root tissue infected as evidenced by lesions. Species of Asparagus susceptible to F. o. f. sp. asparagi were used to determine the optimal spore concentration for disease development and to evaluate the virulence of several Michigan isolates of F. o. f. sp. asparagi and F. moniliforme. Inoculations with 1 ml of a conidial suspension (10⁶ conidia per milliliter) of F. o. f. sp. asparagi or F. moniliforme produced consistently high disease ratings on susceptible seedlings. Disease reactions of resistant and susceptible species of Asparagus in the in vitro assay were compared with those obtained from transplants in greenhouse evaluations. Seedlings of A. sprengeri and A. myersii were rated as resistant in the in vitro assay, whereas A. plumosus and A. setaceous ‘pyrimidalis,’ A. palestinus, A. stipularis, and all cultivars of A. officinalis were susceptible. This method represents a rapid, relatively inexpensive technique for evaluating Asparagus spp. germ plasm for resistance to Fusarium crown and root rot.