Survival analysis for estimating risk factors in incubation period of Didymella pinodes on pea (Pisum sativum L.)

Ascochyta blight caused by Didymella pinodes (Berk. et Blox.) Vestergr. is one of the most devastating diseases, causing severe damage in pea. A new statistical approach based on factor risk using non- parametric and semi parametric survival analysis was used in this study. Different hypotheses dealing with factors that might influence the incubation period were tested. Survival analysis using Kaplan-Meier estimates and Coxproportional hazards was performed for data analysis. During these investigations, incubation period was regressed against leaf wetness duration (LWD), inoculum concentration, plant age and isolate’s aggressiveness. The non-parametric Kaplan-Meier test had shown the importance of leaf wetness duration, inoculum concentration and plant age in the survival curve for the incubation period. Thus, the lowest median incubation period was obtained under the LWD of 72 h. This was 9.0 days (95% CI 8,402-9,598 days). On the other hand, the highest inoculum concentration induced the shortest incubation period with a median value of 9.0 days (95% CI 7,772-9,531 days). Likewise, using the semi parametric Cox proportional hazard regression, only two covariates (leaf wetness, inoculum dose) were associated with survival time with an hazard ratio of 1.144 p=0.03) and 1.015 (p<0.0001). Moreover, neither the plant age inoculation nor the isolate presented a significant hazard ratio for the best fit of the model.