Interactive Effects of Climatic Variables on Occurrence and Severity of Witches' Broom Disease of Lime in Oman

Introduction: Witches’ Broom Disease of Lime (WBDL) severely threatens citrus production in Oman and other subtropical regions. However, the influence of climatic factors on its spread and intensity remains insufficiently explored. This study investigates the individual and interactive effects of temperature, humidity, rainfall, and wind on WBDL occurrence and severity. Methods: Field data were collected from 1,745 lime trees across 15 orchards in North Al-Batinah, Oman, between April 2021 and April 2022. Probit and Tobit regression models were employed to estimate the probability of WBDL occurrence and the degree of severity, respectively. Interaction terms among climatic variables were introduced to capture synergistic or suppressive effects. results: Out of 1,745 lime trees surveyed, 64% exhibited WBDL symptoms, with severity averaging 8.2% but varying widely. Temperature (avg. 40.1°C), relative humidity (avg. 52.8%), and rainfall (avg. 4.4 mm) were positively associated with disease occurrence and severity. In contrast, wind speed (avg. 9.6 km/h) negatively affected both. Seasonal patterns revealed higher incidence during hotter quarters (Q2–Q3), with symptom prevalence rising from 48.7% in Q1 to 78.2% in Q5. Interaction terms showed that simultaneous increases in temperature and humidity significantly amplified disease impact, while the interaction of rainfall and humidity reduced it. Results: A 1°C rise in temperature increased disease severity by 2.7%, while rainfall heightened occurrence and severity by 12.9% and 6.6%, respectively. Conversely, a 1 km/h increase in wind speed reduced occurrence by 10.9% and severity by 5.3%. Interaction analysis showed that high temperature and humidity combinations intensified WBDL, whereas rainfall and humidity interactions suppressed both. Disease prevalence peaked during summer, highlighting strong seasonal effects. Discussion: Climatic variables significantly shape WBDL dynamics through nonlinear interactions. Wind mitigates transmission, while high temperature and humidity favor disease proliferation. Conclusion: Temperature, rainfall, and humidity are major climatic drivers of WBDL, whereas wind acts as a limiting factor. Understanding these effects supports adaptive management through resistant cultivars, optimized planting sites, and protected cultivation to sustain lime production in Oman and similar subtropical agroecosystems.