Environmental, Genetic and Structural Interactions Affecting Phytophthora spp. in Citrus: Insights from Mixed Modelling and Mediation Analysis to Support Agroecological Practices

Abstract

This study investigates the complex interactions between environmental, genetic, and structural factors that influence two key parameters: the density of Phytophthora spp. propagules per gram of dry soil (NPSS) and the number of colonies (NC). Using advanced statistical approaches, we examined the combined effects of variables such as soil moisture, dry weight, temporal fluctuations, and rootstocks. The results show a significant linear relationship between NPSS and soil moisture, as well as a strong positive correlation between NPSS and NC. Genetic analyses reveal a predominant contribution of environmental factors to trait variability, with high phenotypic coefficient of variation (PCV) and low broad-sense heritability. Mixed models highlight the synergistic impact of soil moisture, NC, and dry soil weight on NPSS, as well as significant temporal effects. Mediation analysis confirms that soil moisture influences NPSS primarily through an indirect effect transmitted by NC, with a mediated proportion exceeding 94%. Finally, multivariate analysis reveals significant differences between rootstocks, with Citrus Volkameriana B2 28613 (R4) and Mandarin Sunki x P.T. B2 38581 (R7) standing out as the most performant. These results highlight the importance of an integrated management of environmental variables and rootstocks to optimize soil productivity and agronomic quality. The implications of this study provide a solid foundation for guiding genetic improvement and soil management strategies, balancing environmental constraints and the opportunities offered by targeted genetic selection.