نوع مقاله : مقاله پژوهشی
نویسندگان
1 بخش تحقیقات زراعی و باغی، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی فارس، سازمان تحقیقات و آموزش کشاورزی، شیراز ، ایران.
2 بخش تحقیقات فنی و مهندسی کشاورزی، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی فارس، سازمان تحقیقات و آموزش کشاورزی، شیراز، ایران
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Pomegranate (Punica granatum) is a subtropical tree that is cultivated in many regions of Iran with . temperate and subtropical climates. In recent years, climatic changes and decrease in annual rainfall prevailed in the most pomegranate growing areas has affected the growth and fruiting of trees in pomegranate orchards. In order to evaluate the responses of ‘Rabbab’ pomegranate tree to different irrigation regimes, the present study was carried out during 2019 and 2020 in Koh-Chenar city in Fars province. The experiment was conducted in the form of a randomized complete block design with three replications in two consecutive years The irrigation regimes applied to the pomegranate trees consisted of control (orchard irrigation with 15,000 m3 of water), irrigation at 35%, 50%, 65% and 80% soil moisture depletion. The results showed that reducing the amount of irrigation water decreased yield by %22 to % 40 in all low irrigation treatments. Irrigation at 65 and 80% of moisture depletion also significantly decreased the fruit weight by 12 to %28 and aril dry weight. The highest amount of proline (0.476 µmol/ leaves fresh weigh) was observed in 80% soil moisture depletion. The activity of antioxidant enzymes also increased with the reduction of irrigation water, so that the highest activity of catalase enzymes (0.47 u/mg protein/min.) and superoxide dismutase (1. 0.47 u/mg protein/min) were observed in 50% soil moisture depletion. According to the changes in antioxidant activities and the average of fruit weight, aril weight and percentage of aril paleness, it can be concluded that ‘Rabbab’ pomegranate tree can tolerate water deficit up to 50% soil moisture depletion and maintain fruit quality, but the higher levels of soil moisture depletion (65 and 80%) cause a decrease in the quantitative and qualitative characteristics of the fruit and yield, and increase the percentage of aril paleness.
کلیدواژه‌ها [English]
Extended Abstract
Introduction
Pomegranate (Punica granatum) is a subtropical tree that is cultivated in most regions of the Iran. The main areas of pomegranate cultivation in Iran have a hot and dry climate, so drought and heat stress are one of the most important problems of Iranian pomegranate orchards. This has affected the physiological characteristics of the tree, resulting in a reduction in the quantity and quality of the fruit. Some physiological abnormalities such as aril paleness and fruit cracking in pomegranates fruits are caused by water stress, therefore, adjusting the irrigation regimes and determining the tolerance of pomegranate to water deficit is very important. In this research, the quality of pomegranate fruits on different water irrigation regimes were investigated in order to determine the tolerance of pomegranate to drought conditions.
Material and methods
For evaluation of different responses of ‘Rabbab’ pomegranate trees and fruits to various irrigation regimes, present study was carried out on uniform ‘Rabbab’ pomegranate trees in Kooh-chenar region, Fars Province, south of Iran. The experiment was conducted in two consecutive years in the randomized complete block design with 3 replications on 15-year-old pomegranate trees. Treatments included: Control (irrigation according to recommended plans suitable for commercial fruit production) and irrigations to field capacity at 35%, 50% ,65% and 80% of soil moisture depletion. In this experiment, some vegetative characteristics such as leaf dry weight, chlorophyll content, leaf proline content, antioxidant activity (superoxidase, catalase and peroxidase) were measured. Fruit characteristics such as aril weight, fruit weight, yield, anthocyanin and phenol contents, acidity and total soluble solids (TSS) of fruit juice were also measured. The amount of fruit juice polyphenols was evaluated using HPLC.
Results and discussion
Our results indicated that ‘Rabbab’ pomegranate cultivar is able to tolerate mild irrigation deficit (50% soil moisture depletion), since under such conditions, parameters such as leaf chlorophyll content and leaf dry weight did not change and the activity of catalase and superoxide dismutase enzymes raised to the highest amount. The highest amount of proline (0.476 molar in 1g leaf fresh weight) was observed in 80% soil moisture depletion treatment. Regarding fruit characteristics, the reduction of irrigation water resulted in a decrease in fruit weight from 202 g in the control treatment to 137 g in the 80% soil moisture depletion treatment. A similar decrease was observed in arils weight and the yield. The highest aril fresh weight (22 g) was observed in control plants, whereas the lowest weight (15.5 g), was observed in soil moisture depletion of 80%. Different irrigation regimes did not significantly affect the number of arils dry weigh. The highest yield was observed in control trees (89 kg per tree), which was significantly superior to all irrigation treatments. The highest percentage of aril paleness (60%) was observed in 80% soil moisture depletion, while other treatments showed any no significant difference with the control, this could be due to the disturbance in photosynthesis and plant metabolism that occurs in plants subjected to severe conditions. In the present study, fruit quantitative parameters such as fruit weight and aril fresh weight decreased in low irrigation conditions, which was consistent with previous studies. The reduction of irrigation water caused a decrease in nitrogen absorption and increase in the accumulation of potassium in the leaves, so that the minimum amount of nitrogen was observed in 80% soil moisture depletion, and maximum amount of potassium obtained in 65% soil moisture depletion The analysis of polyphenols in pomegranate fruit juice showed that the highest hesperidin, gallic acid and ellagic acid amount observed in the 80% soil moisture depletion treatment, which had a significant difference with most of the treatments and the control. The amount of coumaric acid was the highest in the 35% soil moisture depletion treatment, while the highest amount of vanillin was observed in the 50% soil moisture depletion treatment. Under drought stress condition, the synthesis of some polyphenolic compounds changes, which may be related to modifications in the activity of certain genes.
Conclusion
According to the results of this study, ‘Rabbab’ pomegranate could tolerate mild to moderate drought stress. Reducing irrigation water to 50% soil moisture depletion had a small effect on some characteristics, such as leaf chlorophyll concentration, aril dry weight and plant performance, whereas reducing the soil moisture to more than 50% resulted in an increase in fruit disorders like aril paleness and significant decrease in quantity and quality of the fruit.
)