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Disease Note.

Phytophthora Leaf Blight of Jojoba (Simmondsia chinensis) in Arizona. S. M. Alcorn, Department of Plant Pathology, University of Arizona, Tucson 85721. T. V. Orum, and M. E. Matheron. Department of Plant Pathology, University of Arizona, Tucson 85721. Plant Dis. 73:444. Accepted for publication 28 February 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0444C.

On 19, 21, 24 and 29 August 1988, approximately 500,000 jojoba plants (Simmondsia chinensis (Link) Schneider), about 22 cm tall, in pots and outdoors in a western Arizona nursery, received 0.5-4.83 cm per day of intense rain, totaling 11.81 cm. Much dust accompanied the first storm. Plants were also irrigated by overhead sprinkler 5-7hr each day on 18,19, and 26 August. During these 12 days, temperature ranged from 22 to 39C. Within a few days of the last storm, many leaves on approximately 1% of the plants(especially those on the windward side of the nursery) developed one more tan lesions. These leaves frequently abscised, particularly when petioles were infected. Phytophthora parasitica Dastur was consistently isolated from the necrotic spots by culturing sections from the margins of lesions on 2% water agar. Radial growth of the fungus on V-8 agar occurred at 19 through 37 C but not at 40C; oprimal growth was between 27 and 34C. Pathogenicity was confirmed by seperate inoculations of detached and attached leaves with zoospore suspensions from three isolates. Typical lesions developed within 5 days after incubation under high humidities at 30 C. P. parasitica was reisolated from these leaves and from 11 of 13 nodes bearing leaves with basal lesions. The fungus also was isolated from soil in each of five examined containers by baiting, using green fruits from pears (Pyrus communis L.), then subculturing on 2% water agar from lesions on the fruits. Thus, it is possible that the foliar infections resulted from either infested splashed soil or windborne dust. Althuogh P. parasitica has been recovered from rotting roots of jojoba (1), this is the first report of this fungus causing a foliar disease of this plant.

Reference: (1) M.E. Stanghellini. Jojoba Happenings 20:4, 1977.