Heat level in chile pepper in relation to root and fruit infection by Phytophthora capsici

Abstract

Phytophthora blight, caused by Phytophthora capsici Leon., is a major plant disease that limits chile pepper (Capsicum annuum L.) production in New Mexico. Chile pepper producers in New Mexico report that Phytophthora blight symptoms appear to develop slower and its incidence is lower in hot than in nonhot chile pepper cultivars. There has been no previous systematic assessment of the relationship of chile pepper heat level to chile pepper response to P. capsici. Three hot ('TAM-Jalapeño', 'Cayenne', and 'XX-Hot') and two low-heat ('NuMex Joe E. Parker' and 'New Mexico 6-4') chile pepper cultivars were inoculated at the six- to eight-leaf stage with zoospores of P. capsici under greenhouse conditions. Additionally, detached mature green fruit from three hot ('TAM-Jalapeño', 'Cayenne', and 'XX-Hot') and one low-heat ('AZ-20') chile pepper cultivars were inoculated with mycelium plugs of P. capsici under laboratory conditions. When plant roots were inoculated, Phytophthora blight was slowest to develop on 'TAM-Jalapeño' in contrast to all other cultivars. All 'TAM-Jalapeño' plants showed wilting symptoms or were dead ≈22 days after inoculation compared with 18,15,14, and 11 days for 'NuMex Joe E. Parker', 'New Mexico 6-4', 'XX-Hot', and 'Cayenne', respectively. When fruit were inoculated, lesion length ratio was significantly higher for 'TAM-Jalapeño' fruit than for 'Cayenne', 'XX-Hot', and AZ-20' fruit. Similarly, lesion diameter ratio was higher for 'TAM-Jalapeño' fruit than for fruit of other cultivars. Furthermore, mycelial growth on lesion surfaces was more extensive on 'TAM-Jalapeño' fruit than on fruit of other cultivars. Results from this study indicate that there is little or no relationship between heat level and chile pepper root and fruit infection by P. capsici.