Pathogen and disease characteristics of marigold black spot in Beijing and surrounding areas

Abstract

Annual epidemics of black spot, a serious disease of marigold (Tagetes erecta), developed in Beijing and surrounding areas from 2011 to 2015. Alternaria tagetica was isolated from marigold showing symptoms from Beijing and Hebei province, and pathogen characteristics and meteorological factors influencing disease development were investigated. The optimum growth temperature of the fungus was 20–25 °C. Field experiments conducted from 2011 to 2014 to evaluate diseased residual branches indicated that marigold residues from the previous year are a likely source of primary inoculum. Regression analysis showed that temperature and precipitation were explanatory factors for disease development from 2013 to 2015. Structural equation modelling indicated that the contributions of temperature degree‐day and rainfall to disease intensity were 27% and 30%, respectively. Augmented Dickey–Fuller test results indicated stability in the residual sequence and co‐integration between the variables daily average temperature, daily average precipitation, daily average humidity and daily disease intensity. Error‐correction modelling showed that temperature, lagged order of temperature, precipitation, lagged order of precipitation, lagged order of disease intensity and the error term were significant. Research indicated that A. tagetica was the primary pathogen of marigold black spot, and that crop rotation could play a useful role in management of the disease, whilst increased rainfall and reduced temperature provide superior conditions for disease spread and infection. There is potential for the results of this study to be used by municipal agriculture authorities in the prediction of marigold black spot in Beijing.