جستجوی مقالات مرتبط با کلیدواژه « ornamental hollyhock » در نشریات گروه « باغبانی »

 Climate change predictions indicate that drought and extreme heatwaves will become more frequent and extreme in many regions. Drought is the main abiotic stress that severely reduces plant yield across the globe. Thus, this may have negative consequences for the agricultural soils, as it limits the availability of water and nutrients to soil microorganisms and plants that develop on these soils. To cope with this situation, the use of organic amendments is the best option. Recent studies have shown that the application of organic fertilizers can affect soil moisture and thus, mitigate the negative effect of climate change on that parameter. Organic amendments increase soil organic matter content thus improving soil physical, chemical, and biological properties, and therefore, can confer drought resistance to soils. The application of organic residues has been presented as a great strategy against soil degradation in semiarid environments. However, the interactions between organic amendments and drought in hollyhock plants are not fully known. Here, we evaluate whether the organic amendment influences the physiological traits of hollyhocks and soil properties under drought conditions.

 The experiment was conducted in the research field at Ferdowsi University of Mashhad, Iran. The experiment consisted of three factors (cultivars, organic amendments, and drought) with organic amendments and drought having four and three levels, respectively. Drought treatments were controlled by a TDR at 80, 60, and 40% FC. The three sources of organic amendments were used cow manure, rice hull and wheat straw. Seeds were planted in cocopeat, perlite, and peat mixture trays in the greenhouse with an average temperature of 20 °C and under a photoperiod of 14 hours of light and 10 hours of darkness with a light intensity of 400 μmol-1 m2. In the 5-6 leaf stage, seedlings were transferred in pots (18 cm high and 8 cm in diameter) containing field soil. The plants were transferred to the field with four different substrates (field soil, field soil + manure, field soil + rice hull, and field soil + wheat straw) and were exposed to drought stress for one month during the flowering stage. This analysis examined both the physical and chemical properties of the soil, including changes in the macroelements nitrogen, phosphorus, and potassium.

 Soil nitrogen changes were significantly affected by the interactions of ecotype with drought, ecotype with the medium, and drought stress with medium. The highest nitrogen changes were recorded in Mashhad ecotype under 80% FC. Nitrogen content in amended soil had an increasing trend during the experiment, but the amount of nitrogen had a decreasing trend in soil. In all media under stress, the amount of soil phosphorus was increased and the highest amount of phosphorus was observed in soil + manure at all irrigation regimes. The highest amount of potassium in both ecotypes was observed in soil + manure. The amount of potassium in amended soils under stress significantly increased, but in all organic amendments with increasing drought stress from 80 to 40% FC, the potassium content decreased. In both ecotypes, soil salinity was increased in all culture media. Han et al. (2016) stated that the amount of nitrogen, phosphorus, and potassium in the amended soil was higher than the substrates containing chemical fertilizer. The medium EC was alkaline at the end of the experiment and the salinity of the culture medium increased compared to the control. This study revealed a negative correlation between electrolyte leakage and dry weight in hollyhock plants. Furthermore, all measured physiological and growth parameters were significantly affected by the treatments. Notably, the Mashhad ecotype grown in soil supplemented with animal manure at 80% field capacity (FC) exhibited the highest levels of physiological traits (SPAD and relative water content) and growth index (dry weight).The application of manure + soil by providing macro elements reduces the negative effects of drought stress.

 The type of crops grown in arid and semi-arid regions should be reconsidered. Also, some plants with high water requirements should be replaced with plants with low and unexpected water requirements. Because hollyhocks are low-expected plants that grow well in drought areas, so they can be considered as suitable species for cultivation in low-input systems and can tolerate drought situations by 40% FC in amended soil.

The Hollyhock (Alcea rosea) is a summer flowering biennial plant that is native to China and belongs to the Malvaceae family. It is one of the most valuable ornamental plants, whose 36 species are cultivated in Iran. It is an increasing garden escape, especially in urban areas, and is usually found at foot of walls, in ruderal areas, and in cracks of pavements and old walls. Also, it is sometimes seen on riverbanks (for instance on dikes of the river Maas), dumps or road- and railway banks. Alcea rosea has been used as an herbal plant in folk medicine for treatment of different diseases such as common cold and cough. This plant is antiphlogistic, astringent, demulcent, diuretic and expectorant. Drought is the most significant environmental stress in agriculture worldwide, and improving yield under drought is a major goal of plant breeding. Seed germination and early seedling growth are potentially the most critical stages for water stress. When subjected to drought stress, plant metabolism is interrupted or inhibited by increasing reactive oxygen species (ROS) and lipid peroxidation, resulting in reduced germination, weaker root and shoot growth and even mortality. Plants have evolved oxygen-scavenging systems consisting of non-enzyme antioxidant metabolites, such as proline and various antioxidant enzymes including superoxide dismutase, peroxidase and catalase.

In order to examine the effect of drought stress on germination indexes, various antioxidant enzyme changes and non-enzyme antioxidant metabolites in Alcea rosea, an experiment was conducted in complete randomized design with three replications. The drought stress treatment was conducted in five levels with osmotic pressures 0, -2, -4, -6, and -8 bar and with using PEG (Poly Ethylene Glycol 6000) on two ecotypes of Alcea rosea (ecotype 1= Mashhad and ecotype 2= Tehran). The seeds are at first sterilized with hypo chloride sodium for two minutes and then washed superficially three times with distilled water. 25 seeds were transferred to a glass petri dish with 10 cm diameter, and for the duration of the experiment, 5 ml solution with different levels was added to each petri dish. After 14 days at 25±1 ºC temperature, the number of geminated seeds in each day was counted and recorded. In the first part of the experiment, after the end of the germination period, the following growth parameters were measured: germination percentage, germination rate, root and shoot length, and the fresh weight of seedling. In the second part, the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), malondialdehyde content, lipid peroxidation in terms of malondialdehyde (MDA) content, and proline index were measured.

The ecotype, drought treatments and their interaction had significant effects on growth parameters (germination percentage, germination rate, radicle and plumule length, and seedling fresh weight), as well as physiological and biochemical parameters (SOD, POD, CAT, MDA and proline). The highest germination parameters were recorded at Mashhad ecotype. Germination percentage and germination rate were severely affected by drought. Maximum percentage of germination (36) was recorded at control group followed by 32.1 at -2 bar and -4 bar PEG treatments in ecotype 1. Germination percentage in two ecotypes further declined to 33% at -8 bar compared to the control treatment. In both ecotypes, plants had the highest germination rate in control media (zero osmotic potential) but germination rate decreased significantly by decreasing water potential. Germination rate of control seeds of ecotype 1 was 11.7, while that of ecotype 2 was 8. 3. Germination rate in two ecotypes further declined to 56% and 38 %, at -8 bar compared to the control treatment, respectively. Ecotype 2 displayed a significant reduction in radicle and plumule length compared to the ecotype 1. Generally, the radicle and plumule length decreased significantly in relation to the drought stress caused by PEG. Ecotype 2 in -8 bar PEG treatment had the highest (41 and 32%) decrease in radicle and plumule length compared to the control temperature. In two ecotypes (Mashhad and Tehran) of Alcea rosea, increasing PEG concentrations resulted in a decrease in fresh and dry weights. Water absorption is the first germination stage. Due to the probable resistance of the ecotype one, water absorption rate is higher, and as a result, the percentage and rate of germination have increased. Ecotype 1 exhibited higher leaf SOD activities in response to -2 bar compared to -8 bar, but the SOD activities in ecotype 2 showed a general increase trend with increases in the PEG concentration. Drought stress resulted in lower antioxidant enzyme activities (POD) in leaves of both ecotypes compared to that observed at the control treatment, but the activity of CAT increased with the increase of drought stress. In both ecotypes, exposure to -8 bar resulted in significantly higher leaf MDA activities. Plants exhibited higher proline in response to -8 bar treatment compared to the control. By increasing the PEG concentration from control to -8 bar, proline content increased about 90 percent. In this experiment, drought stress reduced the rate and germination percentage and delayed subsequent plant deployment. When plants are subjected to drought stress, their metabolism is interrupted or inhibited by increasing reactive oxygen species (ROS) and lipid peroxidation, resulting in reduced germination, weaker root and shoot growth and even mortality. The recent experiment showed that the activity of two superoxide dismutase and peroxidase enzymes decreased with increasing drought stress, and the activity of the catalase enzyme increased; this is in agreement with the results reported by other studies. On one hand, the increase in the activity of the catalase enzyme indicates that it is perhaps the most important enzyme involved under drought condition, which increased over the course of 14 days. On the other hand, limiting the activity of enzymes and increasing the amount of proline showed that increasing the resistance to drought stress in the plant depends on the accumulation of contaminating substances such as proline.

Due to the higher resistance of the ecotype 1 and increase in water absorption, the percentage and rate of germination were increased. If water absorption is disturbed by the seed, the germination activity is slowly applied and the later growth of the roots will decrease the germination rate. Therefore, it seems that Mashhad ecotype with increase of catalase and proline has the highest drought tolerance compared to the other ecotype at germination stage. There was a significant correlation between germination percentage with SOD and POD.