Document Type : Research Article
Authors
1 Department of Agriculture, Payame Noor University (PNU), Tehran, Iran
2 Crop and Horticulture Science Research Department, Markazi Agricultural and Natural Resources Research and Education Center (AREEO), Arak, Iran
Abstract
Introduction
Mineral nutrients (macro and micro) and polyphenolic compounds are natural components of many fruits and play an important role in maintaining the quality and nutritional value of the fruit. Therefore, optimal management of plant nutrition in order to increase the quantity and quality of the product and improve the synthesis of secondary metabolites, especially during fruit growth, is necessary and unavoidable. Nevertheless, in the last decade, the occurrence of pomegranate aril paleness has been reported as a new and pervasive factor in reducing the quality of pomegranate fruit in many countries, including Iran. Therefore, the present research was conducted with the aim of comparing mineral (concentration of iron, zinc and calcium) and biochemical (anthocyanin content) in pomegranates affected by aril paleness and healthy pomegranates of "Malas Saveh" cultivar (year 2022) and then investigating the effect of foliar application of the mineral elements mentioned on the incidence and severity of the aril paleness complication (year 2023).
Materials and Methods
This study was carried out during two years (2022 and 2023) and two independent trials. First, based on the introduced factors affecting the occurrence of pomegranate paleness (temperature, irrigation water and soil salinity), two orchards with medium and high percentage of pomegranate aril paleness (orchard number 9 and 17, respectively) were selected based on the results of Faraji & Karami (2024a). The first trial in 2022 (orchard No. 9): At harvest and after splitting fruits, twenty healthy fruits and affected fruits by the aril paleness disorder were randomly selected and were used for determination of mineral nutrient (Fe, Zn and Ca) and anthocyanin content in the laboratory. The second trial in 2023 (orchard No. 17): In the first phase, 70 trees were selected and labeled, then at the end of September (2022), percent and severity aril paleness of each tree was calculated. In the second phase (2023), based on the results of the first year, 54 trees as experimental unit (with aril paleness percentage>85 and paleness severity of high/very high) were selected from previous trees. Afterwards, a factorial experiment (3×3×2) in a randomized complete block design with three replications and two stages (the beginning of fruit set and the beginning of fruit ripening) were implemented. Experimental treatments included foliar spraying with three concentrations of iron sulfate (0, 2 and 4 per thousand respectively F0, F2 and F4), three concentrations of zinc sulfate (0, 3 and 6 per thousand respectively Zn0, Zn3 and Zn6) and two concentrations of calcium chloride (0 and 4 per thousand respectively Ca0 and Ca4). Then at harvest, the percentage and severity of aril paleness each treatment was calculated.
Results and Discussion
Data analysis using the independent t-test(α=0.05, df=38) for the first trial (2022) showed that, the nutritional value of the affected fruit by aril paleness is anticipated to be far less than that of the healthy fruit; so that except for the Zn concentration, the concentration of Fe, Ca and anthocyanin content in affected fruits were lower than in healthy fruits. Besides, the results of variance analysis for the second trial (2023) showed that foliar spraying with iron sulfate, zinc sulfate and calcium chloride individually or in combination was effective in reducing the occurrence and severity of aril paleness. Comparison the means percentage of aril paleness between the two groups (before and after foliar spraying regardless of the type of treatment combination) based on the dependent t-test (α=0.05, df=16) also showed that foliar spraying was effective in reducing the percentage of aril paleness. On the other hand, the effect of the participation of calcium element in reducing the incidence and severity of aril paleness was significant. In the absence of calcium element, the incidence of paleness was recorded in the range of 60.17-75.00%, and with the inclusion of calcium in the treatment compounds, the percentage of paleness was recorded in the range of 21.83-0.53%. Also, the mean comparison of the double interaction and main effects of elements indicated the synergistic effect of calcium element with Fe and Zn element in reducing the aril paleness disorder. So that, the combination of Fe-Ca and Zn-Ca has been more successful in reducing the aril paleness disorder than the pure application of each element of iron, zinc and calcium.
Conclusion
Overall, the simultaneous application of Zn-Fe in combination with Ca was more effective in reducing of the mentioned traits than other treatments. Therefore, in order to simultaneously reduce the occurrence and severity of aril paleness, spraying with Fe4Zn6Ca4 and Fe4Zn3Ca4 is recommended in two stages of pomegranate fruit development, including the beginning of fruit set and the beginning of fruit ripening.
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