The pomegranate fruit has beneficial effects on human health and very good organoleptic characteristics, which were strong arguments for its promotion in the markets of developed countries that previously did not know much about this crop. The majority of pomegranates are produced in tropical and subtropical parts of the world, but recently, there was an expansion of the cultivated areas due to a greater consumer’s demand. Pomegranate is considered to be adapted to a wide range of climates and soil conditions. In Greece, production was traditionally located in Peloponissos, southern Greece, with a dry and hot Mediterranean climate, using the local cultivar “Ermioni.” Since 2006, its cultivation expanded in northern parts of the country, with more wet and colder climate, with the introduced cultivar “Wonderful,” reaching nowadays about 3.000 ha.

Of the most important cause limiting commercial yield worldwide is cracking (CR). It is induced by differences in the growth rate between peel and flesh of the fruit and the pressure imposed by the quickly expanding arils on the stretched peel (Singh et al., 2020). Cultivars differ in their susceptibility to CR and damages were related with increasing trends in fruit volume, lower Ca ion and higher pectin content in peel, resulting in decreased elasticity (Saei Ahagh et al., 2015). Little is known on the magnitude of the influence caused by changes in environmental parameters on CR on pomegranate or other fruits (Khadivi-Khub, 2015). Rainfall in previously water stressed pomegranate trees induced CR due to an asymmetric increase in fruit turgor pressure; aril turgor increased to a much greater extent than peel turgor (Galindo et al., 2014). In tomato, which is considered as a model system for studying cracking, irrigation together with environmental conditions such as high relative humidity (RH) and radiation that modify the growth rate during ripening also favored fruit cracking (Guichard et al., 2001; Domínguez et al., 2012). Symptoms of RS in pomegranate appear as tiny cracks in the cuticle and corky like surface in the peel; being restricted in only a portion of fruit located mainly in the sides or lower part of the fruit and in some cases covering its surface (Supplementary Photo 1). There is little documentation on RS damages and its causal agents in pomegranate. Russeting is a common physiological disorder in apples, pear, and plums that develops in only some cultivars and occur by stress like unfavorable weather conditions, especially low temperatures in fruit setting, pesticide application at high temperatures, or incompatible pesticide mixtures (Tukey, 1959; Michailides, 1991; Khanal et al., 2013). RS damages may be substantial in cv. “Wonderful,” affecting up to 70% of fruit in some orchards and years in Northern Greece. We have not seen RS damages in fruit from the fully red colored cv. “Acco.”

In recent years a significant number of studies have documented that exogenous salicylic acid act as an effective “therapeutic agent” for plants just like it is for mammals, such as by developing resistance to abiotic stress conditions or providing protection against pathogens (Koo et al., 2020). Acetyl salicylic acid (ASA) is a close analog of salicylic acid and when applied exogenously is converted to salicylic acid spontaneously. Besides this function during biotic and abiotic stress, salicylic acid plays a crucial role in the regulation of physiological and biochemical processes during the entire lifespan of the plant, by affecting a wide range of processes, such as seed germination, photosynthetic processes, growth, flowering, fruit ripening, and others (Rivas-San Vicente and Plasencia, 2011; Koo et al., 2020). However, the above effects of salicylic acid are not always constant depending on the method of application, plant species, the plant developmental stage, and the concentration used (Horváth et al., 2007; Rivas-San Vicente and Plasencia, 2011).

Preharvest foliar sprayings with salicylic or ASA induced a range of beneficial effects such as improvement in fruit size, bioactive compounds, sugars, and organic acids in fruit trees species such as apples (Shaaban et al., 2011; Giannousis, 2012), pears (Cao et al., 2006), sweet cherries (Yao and Tian, 2005; Giménez et al., 2014, 2017; Valverde et al., 2015), oranges (Huang et al., 2008), grapes (Champa et al., 2015; Oraei et al., 2019; García-Pastor et al., 2020b), and plums (Martínez-Esplá et al., 2017, 2018). However information is scarce for pomegranate and especially for the widely grown cv “Wonderful,” being a monoculture for the United States (Chater et al., 2018) and the main cultivar introduced in Greece, Cyprus, and other countries. In the study by Ahmed et al. (2014), application of salicylic acid at 100 ppm, together with various nutrients, reduced CR symptoms in cv. “Manfalouty,” but there was no effect when salicylic acid or nutrients were applied separately. In a recent study, preharvest salicylic acid, ASA, and methylsalicylic acid foliar applications on pomegranate improved the fruits’ quality characteristics and its nutritional status on pomegranate cv. “Mollar de Elche” (García-Pastor et al., 2020a). When applied after harvest in pomegranate fruit cv. “Mollar de Elche,” salicylic acid, or ASA treatments reduced chilling injury during storage (Sayyari et al., 2011b; Sayyari and Valero, 2012).

The aims of the present study were to investigate the effects of: (i) meteorological parameters, (ii) fruit position in the canopy, and (iii) preharvest ASA applications, on the occurrence of physiological disorders, yield parameters, fruit quality, and antioxidant attributes in a commercial pomegranate cv. “Wonderful” orchard during a 3-year study. The study was facilitated with the selection of an experimental orchard that intense symptoms of physiological disorders such as CR and RS were regularly monitored. There is scarce information on the effects of environmental and cultivation parameters on the presence of physiological parameters in pomegranate as well as effects of ASA on cv. “Wonderful.”

The experiments were conducted in a commercial pomegranate (Punica granatum cv “Wonderful”) orchard located in Neochori Imathias, central Macedonia, Greece (40°40’15.49” B, 22°27’53.94” E, 4 masl, Mediterranean temperate climate). The trees were 5 years old, trained in a tree shape, supported with trellises, and planted at 6 × 2 m spacing, in west-east rows. All trees received routine horticultural care.

The fruit maturation periods, during the present 3 year study, were characterized with few rainfalls, which were not related with CR damages. Instead, the first occurrence of CR symptoms, were attributed mainly to fluctuations in T_max (5.5–16.0°C) (r² = 0.801; y = 0.7529 × + 4.0106) and less in T_min (8.0–14.0°C) (r² = 0.225), causing a 7–15% increase in %CR. The pomegranate fruit has thick peel, and it is probable that the pulp and the peel shrink due to temperature difference in a disanalogous proportion and subsequently crack. At a later maturity stage (298 days in 2011 and 288 days in 2012) damages were further accelerated; in 2011 this probably resulted from freezing damage, as temperature dropped to −0.5°C, related with mechanical effects of ice formation within tissues (Burke et al., 1976). To our knowledge, this is the first study that documents relations between fluctuations in meteorological parameters, other than rainfall on the occurrence of CR in pomegranate (Galindo et al., 2014) while changing conditions of temperature or vapor pressure deficit were implicated with CR in tomato (Guichard et al., 2001). In the present experimental orchard, RS damages were extensive, and this was also the case in nearby orchards of cv. “Wonderful,” but not in cv. “Acco,” suggesting that its occurrence is cultivar dependent and favored by local environmental conditions. Similarly to CR damage, RS was induced by temperature fluctuation as suggested by the fact that occurrence was monitored after a change in T_min or T_max in all studied years. The development of RS damage may also be related with increased RH as suggested by the fact that symptoms were more pronounced in (i) years with higher RH (2011 and 2012 vs. 2013), and (ii) in the N- compared with the S-part of canopy, where higher RH would be expected. Moreover symptoms often occurred at the stylar end, where free water may accumulate and were also exacerbated in the skin of fruits covered with paper or plastic bag, compared with unbagged fruits in trees from the present experimental orchard (unpublished data). Similar findings relating RS development with increased RH or water movement were reported in plums (Michailides, 1991) and apples (Tukey, 1959; Knoche and Grimm, 2008). Further studies are required to elaborate the mechanism and causal agents for inducing RS damages in cv. “Wonderful.”

Effects of row orientation on performance of fruit trees trained in hedgerows or other designs are poorly investigated, although a N–S orientation is preferred (Trentacostea et al., 2015). In the present study the experimental orchard was planted in a W–E orientation, which proved to be detrimental for fruit quality as depicted by the presence of substantially higher CR and RS symptoms in the N- compared with the S-, side of the canopy. Conventional wisdom concludes that N-S row orientation leads to lower temperature and less light in the N-side, which may have caused differences in the fruits’ cuticle thickness. A thicker inelastic cuticle is expected to be more prone to CR and was shown to develop in shaded apples increasing their sensitivity of CR (Shutak and Schrader, 1948). Moreover, oranges grown on the shaded part of the tree had a significantly greater percentage of fruit cracking (Li and Chen, 2017).

Moreover, the N-side of the canopy had lower fruit number and yield, without any effect on FFW. It is probable that shading negatively affected flower formation and/or fruit set as this has been reported in other horticultural species (Marini and Sowers, 1990; Hampson et al., 1996; Ferree et al., 2001). Similarly, in a nearby bush trained pomegranate orchard, where inner sprouting was un-removed, the inner part of trees was usually without fruit, while RS symptoms were more abundant. Therefore, it is important to avoid planting in a W-E orientation especially in northern Greece while this may be less critical in southern locations of the tropical and subtropical regions that the majority of pomegranate is grown worldwide.

In the present study spraying 4 or 6 times before harvest at 0.5 mM or 1.0 mM ASA did not alter the presence of CR and SS symptoms. Instead, the ASA sprayings substantially alleviated RS damages by up to 57%. Moreover the peel coloration improved in fruit from the ASA treated trees, as shown by an increase in the% red coloration, a^∗ and C^∗ values and lower L^∗ and H^∗ values. We are not aware of another study on the effects of salicylic acid on russeting in apple, pear, or plums. Previous studies have shown a beneficial role of salicylic acid or its derivatives when applied at pre- or postharvest stage in physiological disorders developing during storage, such as scald in apple (Giannousis, 2012) and reducing chilling injury (CI), and internal browning in pomegranates (Sayyari et al., 2009, 2011a,b; Dokhanieh et al., 2016) and peaches (Wang et al., 2006). In the present study RS damages were apparent in fruits from cv “Wonderful” but not cv. “Acco.” In the latter cultivar, the skin has a better coloration being fully red colored and perhaps the beneficial effects of ASA on RS symptoms in cv “Wonderful” may be related with effects on red pigmentation in the skin tissue.

Anthocyanins contribute to the red/purple color of pomegranates in peel or juice and the predominant class of anthocyanins recovered in pomegranate juice belongs to the cyaniding, compared with the delphinidin and pelargonidin groups (Beaulieu et al., 2015), which were also the case in the present study. The Dp3,5 and Cy3,5 contents were greater compared with the Dp3 and Cy3 contents. An increase in the juice anthocyanin concentration especially in the 1.0 mM ASA and less in the 0.5 mM ASA compared with the control was found in the present study, while1.0 mM ASA induced a more pronounced increase in Cy3,5 compared with the rest measured anthocyanins and in cyanidins compared with delphinidis. ASA sprayings also improved TAC_DPPH and SSC contents in juice. The above beneficial effects of ASA on fruit quality attributed were also documented in other studies on pomegranate (Sayyari et al., 2011b; Sayyari and Valero, 2012; García-Pastor et al., 2020a) or other fruit species (apples, Giannousis, 2012; pears, Cao et al., 2006(sweet cherries, Yao and Tian, 2005; Giménez et al., 2014, 2017; Valverde et al., 2015; oranges, Huang et al., 2008(grapes, Oraei et al., 2019; García-Pastor et al., 2020b; plums, Martínez-Esplá et al., 2017, 2018). The pomegranate cv. “Wonderful” is known to have high antioxidant contents in juice, compared with other cultivars (Pantelidis et al., 2012; Chater et al., 2018), and therefore, a further increase by foliar sprays with ASA may be less important from a commercial point of view, compared with the improvement in the external fruit appearance such as lowering RS symptoms and better red coloration documented in the present study (Supplementary Photo 2).

There were no substantial effects of ASA treatment on yield-related parameters; however, there was a trend in producing heavier fruit as suggested by an increase in total FFW, decrease in the %fruit in 200–350 g (smaller size) and increase in the %fruit of 351–500 g and 501–650 g size categories. There were no effects of ASA treatment on% edible portion,% juice and 100 seed weight. As expected the harvested fruit number was not affected by the ASA treatment, since the foliar applications started after 2 or 3 months of fruit development (August 19, 2011 and July 17, 2012). Similar to our findings on increasing fruit yield-related attributes on pomegranate were results on sweet cherry (Giménez et al., 2014), plum (Martínez-Esplá et al., 2017, 2018), grapes (Marzouk and Kassem, 2011; Champa et al., 2015; García-Pastor et al., 2020b), and apples (Shaaban et al., 2011). Increases in productivity by salicylic acid or its derivatives such as ASA were previously attributed to enhanced leaf area, photosynthetic pigments concentration in leaves, photosynthetic rate, and translocation of sugars from leaves to fruit; however, a controversial role on plant growth depending on cultivar, its concentration, plant growth conditions, and developmental stages has been reported (Rivas-San Vicente and Plasencia, 2011).

The present study reports for the first time that pomegranate CR and RS were induced by temperature fluctuations during the fruit maturation period, and this parameter needs to be considered before establishing an orchard where temperature usually drop during the fruit maturation period. Extensive damages from RS were also reported in the present study that was further related with increased RH and water accumulation. Planting in a W–E direction should be avoided at least in higher latitudes as in the N- compared with the S- side of the canopy, CR and RS symptoms were greater, and fruit yield was lower. ASA is a natural and safe compound, and foliar sprays at 0.5 or 1.0 mM proved to have beneficial effects on juice antioxidant contents, but more importantly on fruit appearance, they are shown as a reduction of RS symptoms and color improvement.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author/s.

PD conceived the project and wrote the manuscript. GP and PD designed the experiment and executed the field and laboratory work. SV undertook the anthocyanin, organic acid, and mineral content analyses. All authors have read and approved the final manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.