Verticillium wilt, caused by Verticillium dahliae, is a common disease of chile pepper (Capsicum annuum) in New Mexico. In August of 2007, wilted plants with vascular discoloration in the stem typical of infection by V. dahliae occurred in several fields in Luna County in southern New Mexico. In one field, Verticillium wilt incidence was between 60 and 70%. Approximately 30% of the field was infested with Physalis wrightii (Wrights groundcherry) and Anoda cristata (spurred anoda), and 60% of the field was infested with Ipomoea purpurea (tall morningglory). Except for vascular discoloration found in a few plants of Wrights groundcherry and spurred anoda, there were no other symptoms observed in the weeds present. Previously, Wrights groundcherry and spurred anoda were demonstrated as hosts to V. dahliae (2); however, to our knowledge, tall morningglory was not. A 5-cm segment was cut from the lower part of the stems and upper part of the tap roots of six tall morningglory plants and two chile pepper plants. The segments were washed, surface disinfested for 2 min in 0.5% sodium hypochlorite, and cut into pieces that were plated onto water agar. Mycelial colonies emerging from the pieces were transferred to either potato dextrose agar, prune extract agar, or Czapek-Dox agar medium. Putative V. dahliae isolates from tall morningglory and chile pepper plants were identified based on characteristic morphological features when cultured on prune extract medium (2,3). In addition, PCR of fungal DNA and sequencing the amplicons using primer pair ITS4/ITS6 showed a 99% homology with the sequence of the rDNA ITS of V. dahliae (1). Pathogenicity tests were conducted with two isolates of V. dahliae from tall morningglory and one from chile pepper. In the first of two methods, four pots were infested with conidia of each isolate (2 × 107 conidia per 500 cm3 of soilless mix) and planted (five seeds per pot, thinned to three seedlings) with chile pepper cv. AZ-20, which is susceptible to V. dahliae. Three noninfested pots served as the control. Pots were placed in a growth chamber at 26/20°C day/night temperature. In the second method, plants (cv. AZ-20) at the 6- to 8-leaf stage were inoculated in a greenhouse with V. dahliae by dispensing 5 ml of a conidial suspension (4 × 106 conidia/ml) into the root plug prior to transplanting. Four root plugs were inoculated per isolate and there were three noninoculated root plugs. Both experiments were repeated once. Isolates of V. dahliae recovered from tall morningglory and chile pepper were pathogenic on chile pepper. Leaf chlorosis, leaf drop, wilting, and vascular discoloration were observed within 8 weeks after sowing into infested soil or within 6 weeks after inoculation into the root plugs of transplants. No symptoms were observed on noninoculated plants. V. dahliae was reisolated from the stems of all symptomatic plants. To our knowledge, this is the first report to document the recovery of V. dahliae from tall morningglory and its pathogenicity on chile pepper. References: (1) P. V. Pramateftaki et al. J. Fungal Genet. Biol. 29:19, 2000. (2). S. Sanogo and M. Clary. Plant Dis. 87:450, 2003. (3) P. W. Talboys. Plant Pathol. 9:57, 1979.
Management of Verticillium Wilt of Avocado Using Tolerant Rootstocks
