Influence of chile pepper heat level on root and fruit infection by Phytophthora capsici

Field observations by chile pepper (Capsicum annuum) producers in New Mexico indicate that symptoms of Phytophthora blight (caused by Phytophthora capsici) develop slower and its incidence is less in hot than in non-hot chile pepper cultivars. This study was conducted to provide a systematic assessment of the relationship of chile pepper heat level to chile pepper response to P. capsici. Three hot (TAM-Jalapeno, Cayenne, and XX-Hot) and two low-heat (NuMex Joe E. Parker and New Mexico 6-4) chile pepper cultivars were inoculated at the 6- to 8-leaf stage with zoo-spores of P. capsici. Additionally, detached mature green fruit from three hot (TAM-Jalapeno, Cayenne, and XX-Hot) and one low-heat (AZ-20) chile pepper cultivars were inoculated with mycelium plugs of P. capsici. When plant roots were inoculated, Phytophthora blight was slowest to develop on TAM-Jalapefio in contrast to all other cultivars. When fruit were inoculated, lesion length ratio and lesion diameter ratio were significantly higher for TAM-Jalapefio fruit than for all other cultivars. Mycelial growth on lesion surfaces was more extensive on fruit of TAM-Jalapeno than on fruit of other cultivars. Results indicate that there is little or no relationship between heat level and chile pepper root and fruit infection by P. capsici.