Environmental drivers of date fruit unripening syndrome in dryland regions of Saudi Arabia

Date Fruit Unripening Syndrome (DFUS), a very recently observed phenomenon, is a devastating non-ripening disorder hindering the Rutab-to-Tamar transition. While observed sporadically since 2019, DFUS became prominent in 2024, disproportionately affecting the economically important Khalas cultivar (40%), followed by Sheshi (19%), Reziz and Ghur (16%), and Shahal (10%) in Al-Ahsa. With the highest incidence in Al-Ahsa (20-30%), followed by Riyadh (10-15%) and Al-Qassim (5-10%), DFUS significantly reduces fruit quality and yield, threatening farmers' livelihoods and the socio-economic stability of date palm-dependent communities. This pioneering study investigated the impact of environmental factors-temperature, relative humidity, solar UV index, heat units, and irradiance-on date palm fruit ripening in Al-Ahsa, Saudi Arabia, from 2019 to 2024, employing ANOVA (<i>p</i> ≤ 0.05) and Duncan's Multiple Range Test for robust statistical analysis. Significant inter-annual temperature variations, including daytime extremes up to 48 °C during Kimri and Khalal stages, potentially disrupted fruit metabolism and ripening. Relative humidity (RH) ranged widely (5-96%), with the Khalal stage particularly sensitive to low humidity, while high RH during the Rutab stage (2023/2024) may have hindered the necessary moisture loss thus negatively impacting the fruit ripening. Increased solar UV exposure, particularly during the Khalal and Rutab stages, may have contributed to DFUS by disrupting fruit pigment synthesis and inducing oxidative stress. Total heat unit accumulation peaked in 2024, while total irradiance declined, potentially hindering sugar conversion and softening during Rutab. Through meticulous field observations and environmental data analysis, we identified critical stressors-such as temperature fluctuations, elevated heat units, and high solar UV indices-as key drivers of DFUS. These findings provide crucial insights into the mechanisms behind DFUS, enabling the development of targeted interventions, such as optimized agricultural practices and potentially genetic solutions, to mitigate the syndrome and protect palm productivity.