Survival analysis to determine the length of latent period of Mycosphaerella pinodes on peas (Pisum sativum L.)


B. Setti*, M. Bencheikh, J. E. Henni and N. Claire

Blight caused by Mycosphaerella pinodes is one of the most devastating diseases of pea that causes yield losses of over 50% in some years and may cause total failure to the crop under epidemic conditions. During this study, a sensitive disease assessment and statistical tool was developed for Mycosphaerella blight on peas, the latent period was used to discriminate between different treatments. The time until appearance of the first pycnidia (latent period length) was recorded. Seedling that did not display any production of pycnidia structure during the 20 days period of observation was recorded as right censored observations. Using non parametric and semi parametric survival analysis, different hypothesis dealing with factors that might influence the latent period was tested. Survival analysis using Kaplan-Meier estimates and Cox proportional hazards were performed for data analysis. During these investigations, latent period was regressed against leaf wetness duration, pea cultivar, inoculum concentration, plant age and isolate aggressiveness. Both the Cox regression and Kaplan-Meier tests had shown the importance of leaf wetness duration, inoculum concentration and isolate aggressiveness on the survival times, thus, the median latent period length was respectively 15 and 16 for tn0203 and md0202. The median for the 3 leaf wetness was 14, 16 and 17 respectively for 06, 48 and 72 h LWD. Both the cultivar and plant age had no significant risk for the pycnidia structure appearance. Likewise, using the semi parametric Cox proportional hazard regression, the 2 covariates namely higher leaf wetness, higher inoculum dose with an aggressive isolate were all associated significantly with survival time. Hence, the hazard ratio was respectively 1.205 and 1.423 for LWD and inoculum concentration respectively. 

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