Temporal progress of roselle (Hibiscus sabdariffa L.) leaf and calyx spot disease (Corynespora cassiicola) in Guerrero, Mexico

Roselle (Hibiscus sabdariffa L.) leaf and calyx spot induced by Corynespora cassiicola is one of the most important diseases that limit production, processing, and commercial use of this crop. The temporal progress of this disease was followed in four production locations in Guerrero, Mexico, during the 2014 and 2015 cycles. Disease incidence and severity were evaluated every 10 days through the 173-day production cycles. Epidemics were evaluated using the area under disease progress curves (AUDPCs) and Weibull model parameters. The highest severity and epidemic rate in calyces and leaves was registered in San Miguel, while the lowest was recorded in Xalpatlahuac in both cycles. Disease incidence in calyces was lower in Xalpatlahuac during both evaluation cycles and in leaves only in the 2015 cycle. The Weibull model properly described the epidemics (r = 0.93-0.99). The highest periods of epidemic growth in leaves were registered during flowering, development of calyces and foliar senescence; and in calyces during their physiological maturation and harvest. Severity on leaves and calyces was correlated with temperature from 20 to 30 degrees C (r = 0.80-1.0) and relative humidity higher than 90% (r = 0.80-1.0) (p < 0.05). The calyces severity was related to the leaves severity (r = 0.90-0.97) (p < 0.01).