Pathogenicity on Chile Pepper of Vertcillium dahliae Recovered from Three Weed Hosts in New Mexico

In July 2002, in the course of field surveys for Verticillium dahliae in chile pepper (Capsicum annuum), three weed species, Physalis wrightii (Wright groundcherry), Anoda cristata (spurred anoda), and Proboscidea louisianica (devil's-claw), were found with symptoms of vascular necrosis in three fields in Luna County and two fields in each Hidalgo and Doña Ana counties in southern New Mexico. Across the three weed species, vascular area with necrosis was approximately 5 to 15%, and was rated on longitudinal crown and stem sections (1). Except for a few plants of P. wrightii that had leaves with necrotic margins in one field in Luna County, no other symptoms were observed. The three weed species were at growth stages between flowering and fruit set. Isolates recovered from the vascular tissue were identified as V. dahliae based on morphological features when cultured on prune extract medium (2). Two isolates of V. dahliae from each weed species, along with an isolate from chile pepper, were grown on potato dextrose agar at 20, 25, or 30°C for 12 days. There was no significant difference in radial growth among isolates at the three temperatures, and maximum radial growth occurred at 25°C. The isolates were tested for pathogenicity on the chile pepper cv. NM 6-4 in the greenhouse. In each of the three trials, 15 plants were inoculated each by root dipping (1) in 20 ml conidial suspension (10⁶ conidia/ml) of each V. dahliae isolate. Control plants were root dipped in sterile distilled water. Symptoms of foliar wilting with 75 to 100% vascular necrosis (1) were observed in all plants 4 weeks after inoculation. V. dahliae was recovered from symptomatic plants (2). To our knowledge, this is the first report that V. dahliae recovered from P. wrightii, A. cristata, and Proboscidea louisianica is pathogenic to chile pepper. Control of Wright groundcherry, spurred anoda, and devil's-claw may be important in the management of V. dahliae in chile pepper. References: (1) R. G. Bhat and K. V. Subbarao. Phytopathology 89:1218, 1999. (2) P. W. Talboys. Plant Pathol. 9:57, 1960.