Multifactorial modeling of nematode-soil interactions associated with citrus decline and implications for sustainable orchard management in southern Iran.

Citrus decline, one of the major challenges in the orchards of Fars and Kohgiluyeh-Boyerahmad provinces, is a multifactorial disorder exacerbated by complex interactions between biotic and abiotic factors. This study aimed to model the interactions between the citrus nematode (Tylenchulus semipenetrans) and the physicochemical properties of the soil, and to evaluate their combined roles in the severity of tree decline. A total of 80 soil and root samples were collected between 2020 and 2022 using standard nematological methods. The data were analyzed using advanced statistical approaches, including ordinal logistic regression (OLR), generalized additive models (GAMs), and partial least squares-discriminant analysis (PLS-DA). The results revealed a significant relationship between nematode population density and decline severity, with soil texture, salinity, saturation percentage, pH, and lime content (Total Neutralizing Value, TNV) acting as moderating factors. The highest nematode densities were observed in light-textured soils with an electrical conductivity ranging from 2.5 to 3.5 dS m⁻¹. Moreover, a significant synergistic interaction was identified among alkaline pH, high TNV, and nematode population density in inducing micronutrient deficiencies. These findings emphasize the necessity of adopting integrated management strategies, including the use of tolerant rootstocks, nematode population regulation, and soil quality improvement, to mitigate citrus decline losses.