نوع مقاله : مقاله پژوهشی
نویسندگان
1 دانشیار، گروه علوم باغبانی، دانشکده کشاورزی، دانشگاه ایلام، ایلام، ایران.
2 دانشیار، گروه تولید و ژنتیک گیاهی، دانشکده کشاورزی، دانشگاه جهرم، جهرم، ایران.
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Aril paleness disorder (APD), also known as aril whitening, is an emerging physiological disorder that severely affect the internal quality, market value, and antioxidant potential of pomegranate fruits. The disorder is characterized by a significant reduction or irregular development of red pigments in the arils. The aril paleness disorder results from a complex interplay of genetic, physiological, environmental, and nutritional factors as well as their interactions. In recent years, aril paleness has become a critical issue in major pomegranate-producing regions, most notably in Iran. This review has synthesized recent findings on the causal factors and management of APD, with a special focus on insights from molecular and biochemical studies. Key causal factors include cultivar susceptibility, reduced expression of anthocyanin biosynthesis genes especially UFGT (UDP-glucose: flavonoid 3-O-glucosyltransferase), deficiency of mineral elements (Ca, Fe, Zn), and environmental stresses such as high temperature and soil and irrigation water salinity stress. In contrary to the earlier hypotheses, emerging evidence suggests oxidative stress and anthocyanin degradation may be secondary to disruptions in their biosynthesis. Effective management of this disorder requires an integrated approach that combines the selection of tolerant cultivars, optimized foliar nutrition (particularly calcium, potassium, iron and zinc). Foliar application of silicon and kaolin, canopy management to reduce heat stress through appropriate pruning and training methods, shading systems, and precise irrigation. This review article has consolidated current knowledge from diverse perspectives, highlights existing gaps in understanding the disorder, and purposes future research directions, including the application of omics technologies and genome editing for developing sustainable solutions for mitigation of this disorder.
Keywords: Pomegranate, anthocyanin, mineral nutrition, UFGT gene, genome editing, environmental stresses.
Introduction
Aril paleness disorder (APD), also referred to as aril whitening, is an emerging physiological disorder that poses a significant threat to the internal quality, marketability, and health-promoting properties of pomegranate fruit (Khademi et al., 2025). The disorder is characterized by a marked reduction or irregular development of red pigmentation in the arils. The aril paleness disorder results from a complex interplay of genetic, physiological, environmental, and nutritional factors. In recent years, this disorder has escalated into a critical challenge in major pomegranate-producing regions, most notably in Iran, causing substantial economic losses and undermining consumer confidence (Asadi et al., 2019).
The susceptibility to the APD is strongly influenced by genotype. Molecular studies have pinpointed a key genetic determinant: a significant downregulation of the UFGT (UDP-glucose: flavonoid 3-O-glucosyltransferase) gene in affected arils (Khademi et al., 2025). This enzyme is crucial for the final glycosylation step in anthocyanin biosynthesis. Its suppression leads to a failure in producing stable, pigmented anthocyanins, which is now considered the primary molecular trigger for the APD, rather than a general oxidative stress response or anthocyanin degradation (Khademi et al., 2025). While other structural genes like PAL and CHS may also show reduced expression, the specific downregulation of UFGT gene is the most consistent biomarker of the disorder.
Physiologically, the APD is intrinsically linked to disruptions in anthocyanin metabolism. Affected arils consistently show a drastically lower total anthocyanin content compared to healthy ones, directly correlates with the loss of red color (Zarei et al., 2024b; Khademi et al., 2025). Nutritional imbalances, particularly deficiencies in key mineral elements, play a pivotal synergistic role. Research indicates that deficiencies in calcium (Ca), iron (Fe), and zinc (Zn) are closely associated with the APD incidence (Karami and Faraji, 2025). Calcium is vital for cell wall integrity, while iron acts as a co-factor for enzymes in the phenylpropanoid pathway. Zinc (Zn) influences antioxidant enzyme systems and carbohydrate metabolism, indirectly supporting secondary metabolite synthesis.
Environmental stresses are major exacerbating factors, demonstrating a clear genotype × environment interaction (Zarei et al., 2024b). High temperatures, particularly during fruit ripening stage, have been shown to suppress anthocyanin accumulation. Similarly, salinity stress from soil or irrigation water can disrupt plant metabolism and nutrient uptake, further intensifying the disorder (Sedaghat et al., 2021). The expansion of pomegranate cultivation into warmer, drier regions has been a significant driver of the APD outbreaks. Effective management of APD necessitates an integrated, multi-pronged strategy. The most promising and immediately applicable approach is application of foliar nutrition.
Recent studies have demonstrated that combination of foliar sprays of calcium, iron, and zinc, applied at key fruit developmental stages (fruit set and onset of ripening), can reduce the APD incidence and severity by up to 40% (Karami and Faraji, 2025). This treatment directly addresses the identified physiological and biochemical deficiencies. Complementary agronomic practices include the use of shade nets to mitigate heat stress and sunburn, precise irrigation management to avoid water stress during critical growth stages, and balanced nitrogen fertilization to prevent excessive vegetative growth that can limit calcium uptake.
For long-term sustainability, the development of tolerant cultivars is paramount. Future research should prioritize several key areas: 1. Development of molecular markers linked to the UFGT gene and other quantitative trait loci (QTLs) for tolerance to enable marker-assisted selection (MAS). 2. Development of tolerant cultivars. 3. Investigating the upstream regulatory networks, particularly the MYB-bHLH-WD40 transcription factor complex, which controls anthocyanin biosynthesis and may be disrupted by environmental stresses. 4. Application of high-throughput phenotyping technologies, such as hyperspectral imaging coupled with machine learning, for non-destructive screening of breeding populations (Khademi et al., 2025). 5. Integration of multi-omics approaches (transcriptomics, metabolomics, and proteomics) to build a holistic understanding of the regulatory and metabolic networks involved in the aril paleness disorder.
In conclusion, the APD is a multifaceted disorder rooted in genetic susceptibility, specific molecular dysfunction (UFGT suppression), mineral deficiencies, and environmental stresses as high temperature. While advanced foliar nutrition application offers a powerful short-term management tool, long-term solutions lie in breeding for genetic tolerance. A concerted interdisciplinary effort combining precision horticulture, molecular biology, and modern breeding technologies is essential to safeguard the future of pomegranate production under the changing climate conditions.
References
Asadi, E., Ghehsareh, A.M., Moghadam, E.G., Hodaji, M. and Zabihi, H.R. 2019. Improving of pomegranate aril paleness disorder through application of Fe and Zn elements. Indian Journal of Horticulture, 76(2), pp.279–288. DOI: 10.5958/0974-0112.2019.00043.4
Karami, S. and Faraji, S. 2025. The effect of foliar spraying of iron, zinc and calcium in the stages of fruit maturity on the incidence and severity of pomegranate (Punica granatum L.) aril paleness. Journal of Horticultural Science, 39(1), pp.139–153 (in Persian). DOI: 10.22067/jhs.2024.89090.1366
Khademi, O., Zarei, A. and Naji, A. 2025. Molecular basis of aril paleness disorder in pomegranate fruit: Insights from anthocyanin biosynthesis genes. Tropical Plant Biology, 18, e70. DOI: 10.1007/s12042-025-09438-9
Zarei, A., Khademi, O. and Erfani-Moghadam, J. 2024b. Differential effects of environmental conditions on the commercially important attributes and postharvest quality of pomegranate fruit. Acta Physiologiae Plantarum, 46, 104. DOI: 10.1007/s11738-024-03724-x
کلیدواژهها [English]
)