Modelling Survival Time to Symptom Expression and Death Among Sweet Potato Crosses Inoculated with Fusarium oxysporum f.sp. batatas

Document Type : Original Article

Authors

1 Taita Taveta University

2 Plant Pathology and Crop Physiology Department, Louisiana State University, Baton Rouge, USA

3 3Berlin School of Business, and Innovation, GmbH, Berlin, Germany

4 School of Plant, Environmental and Soil Sciences, Louisiana State University, USA.

Abstract

Two hundred and six sweet potato genotypes descended from Fusarium wilt resistant Beauregard variety as one of the parents and those without Beauregard as a parent were inoculated with the Fusarium wilt pathogen, Fusarium oxysporum f.sp. batatas. The objectives of this study were to: (i) compare the efficiencies of different models in describing time to symptom expression and time to death among infected sweet potato genotypes and, (ii) develop predictive models. The Kaplan-Meier survival function and actuarial life tables were used for nonparametric modelling while probability plots using the Generalized gamma, Exponential, Weibull, Lognormal and Log-logistic models were used for parametric modelling. The three-parameter generalized gamma model was also used to determine the performance of the simpler nested two-parameter models. The effect of parental resistance level was significant (P = 0.05) for time to death. Genotypes with Beauregard as a parent took longer to die or show symptoms. From the nonparametric analysis, genotypes descended from Beauregard as a parent took on average 43.14 days to die compared to non-Beauregard genotypes that took 33.31 days. Mean time to symptom expression for all models ranged from 11.67 to 12.28 days. In conclusion, it is possible to model survival time using either the parametric Generalized gamma, Lognormal and Weibull models or the nonparametric model.

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