عنوان مقاله [English]
Introduction: Nowadays, horticultural products especially in our country are damaged by the climate change events (rising temperatures, water shortage associated by drought and extreme temperature fluctuations). The greatest economic damage to horticultural crops are caused by winter chilling and / or spring frosts, in which has been increased by seventimes during the last 10 years. Indeed, just during 9 months of 2016-2017 year, the chilling/frost damages were reached to 140 million euro of the total damage value of 240 million euro to agriculture (about 60%). According to the Agricultural Insurance Fund, maximum amount of compensation to farmers of the country was paid to apples, walnuts, grapes, almonds, pomegranates, oranges and pistachios orchardists, respectively. Grape (Vitisvinifera), a member of the Vitaceae family, is the most important horticultural crop in Takestan region, ranking top in producing raisins in Iran. Yearly, horticultural practices in order to reduce the severity of chilling damages to crops cost a lot under orchard conditions. Some of these practices are included burying vines under soil, winter ice-watering, flood irrigation, and turning the heaters on. Nowadays, cheap and fast alternative methods such as anti-freezes spraying havebeen considered to reduce the freeze injuries under orchards. These compounds as mechanical barriers either prevent the ice crystals formation on the sensitive plant tissues or activate the freezing tolerance mechanisms in the plants. Salicylic acid (SA), a type of phenolic acid, is one of the most secondary metabolites in the grape. SA not only plays an important role on the determination of the quality, color and taste of fruit, but also influences on the plant responses into environmental stresses such as drought, chilling, salinity and heavy metals. Natural osmolites such as soluble sugars, amino-acids and ammonium compounds are accumulated inside the plants under natural conditions. Commercial anti-freeze/anti-transpiration compounds on the basis of the mentioned natural osmolites are used to increase the freezing tolerance or postponing the bud break of horticultural crops. For example, Bio-bloom, Tiofer®, Cropaid® and Fosnutren® were used as anti-freeze compounds under almond, cherry, pistachio and apple orchards in Iran. The efficiency of this method to reduce the chilling injuries in vineyards is not well known. Therefore, to consider the effects of plant basis anti-freeze compounds on the freezing tolerance of red seedless grape under Takestan climate conditions, the current experimentation was conducted. In this regard, the important freezing tolerance determining osmolites as well as some of the qualitative and quantitative characters of vines in response to these compounds were evaluated.
Materials and Methods: In order to study the likely increase in grape spring freezing tolerance using the anti-freeze compounds under the orchard, an experiment was conducted as randomized completeblock design (RCBD) with anti-freeze compounds in Agriculture and Natural Resources Research Center of Qazvin during 2012-2013. Minimum monthly temperature during the autumn and winter months was -12.2 °C. The treatments including the spray of SA, Tiofer®, Cropaid®, Bio-Bloom® and water (control) were used on vines during fourphonological stages: before plant dormancy, during bud swelling, start of clustering and during the final clustering on the three red seedless vines per plot. Quantitative and qualitative characters such as cluster weight, yield and total soluble solids (TSS) were measured. Leaves osmolites contents such as proline (Bates et al.,1973) and glycin-betain (Grieve and Grattan.,1983) as well as the status of the freezing resistance index enzymes activities such as Glutathione peroxidase (GPX) (Updhyaya et al.,), Ascorbateperoxidase (APX) (Nakano and Asada,1981) and Catalase (CAT) (Aebi, 1984) were evaluated. All statistical analyses were made using SAS software. The comparison of mean values for the different treatments was made by ANOVA, followed by the Duncan’s test at the significant level of 0.05.
Results and Discussion: The results showed that the anti-freeze compounds resulted in an significant increase in the TSS, cluster weight and yield by 22%, 17% and 26%, respectively and the most effectswas observed in Bio-bloom. Our results regarding the effect of SA on the TSS was in accordance with other researchers (ShokrollahFaam, 2011; Sedighi et al., 2011; Champa et al., 2014;Marzouk and Kasm, 2011). However the effect of other anti-freeze compounds on the quantitative characteristics has not studied yet. Tiofer and Cropaid had no significant effect on the grape cluster weight. Proline content increased significantly using anti-freeze compounds compared to control during 2012-2013. But there was no significant difference between the different anti-freeze compounds for proline content. The most important content of betaine-glysine was observed in SA and Bio-bloom treatments. A decrease in air temperature during 2013 dormancy period resulted in higher amount of osmolytes contents (betaine glycine) and freezing resistance index enzymes activities compared to those of 2012. The most important contents of these enzymes activities were obtained in SA, Tiofer, Cropaid and Bio-Bloom treatments, respectively and the less important content was observed in control.
Conclusions: According to these results the commercial anti-freeze compounds could be useful not only for an increase in the grape spring freeze resistance but also for an improvement in the grape cluster weight, total soluble solids and yield. Osmolytes contents such as such as proline and betaine glycine and enzymes GPX, APX, CAT are significantly higher in anti-freeze treated plants compared to control. Since high levels of soluble solids, mentioned osmolytes and enzymes resulted in an increase in cold resistance in plant, the use of antifreeze as an easy and inexpensive way to increase the cold hardiness of grapes is recommended. These results were obtained with this antifreeze in 5 ppm concentration. Therefore more researches on the other varieties using different concentrations of anti-freeze compounds are recommended.