First Report of White Rust of Arugula Caused by Albugo candida in Argentina

Production of arugula (Eruca sativa) has increased greatly in Argentina. Since 2002, particularly during the fall, a foliar disease has affected commercial crops in Capilla del Señor (northeast of Buenos Aires Province, Argentina). The disease appeared in foci, spreading throughout the whole production field or greenhouse. Severely affected crops were plowed under. Diseased leaves were chlorotic and had white sori that emerged through the abaxial epidermis. Sori corresponded to the white rust agent, Albugo candida (Pers.) Kunze (1). Sporangiophores were hyaline and clavate, and sporangia were globose and hyaline with a mean diameter of 16.2 μm (14.2 to 19.2 μm). Pathogenicity tests were performed by spraying a suspension of 10⁶ zoospores/ml or 5 × 10⁴ sporangia/ml on four healthy 30-day-old arugula plants. Inoculum was prepared by scrapping sporangia from infected leaves. Sporangia were used directly or incubated in sterile distilled water (SDW) for 14 h at 5°C to induce zoospore formation (2). Four additional healthy plants were sprayed with SDW to serve as controls. Plants were kept in plastic bags for 48 h and maintained in the greenhouse thereafter. White rust symptoms, similar to those observed on the original plants from the field, were observed on inoculated plants 10 days after inoculation. To our knowledge, this is the fist report of A. candida on arugula in Argentina. References: (1) K. Mukerji. No. 458 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1975. (2) H. Scheck and S. Koike. Plant Dis. 83:877, 1999.