Basal defoliation, salicylic acid and cyanocobalamin to ameliorate the physiological and biochemical characteristics of flood-irrigated ‘Crimson Seedless’ grapevines in a semi-arid Mediterranean climate

The common grape, Vitis vinifera L., family Vitaceae, native to Southwestern Asia, Central Europe and the Mediterranean region, is one of the world’s most important fruit crops in terms of total production and economic value (Vivier and Pretorius, 2002). The total cultivated area of this crop in 2020 was about 6,950,930 ha with a total production of 78,034,332 t. The top 15 grapevines producers are China, Italy, Spain, France, the USA, Turkey, India, Chile, Argentina, South Africa, Iran, Uzbekistan, Egypt, Australia and Brazil. Egypt ranked the 13^th with a total cultivated area of 71,889 ha and a total production of 1,586,342 t, yielding an average of 22.07 t · ha^–1 (FAO, 2020).

In Egypt, table grapes are ranked second to citrus in terms of production. The semi-arid Mediterranean climate of Egypt is well suited for grape production. Grape cultivation is spread throughout the country, mostly in heavy soils next to the Nile River, as well as sandy soils and newly reclaimed lands in the deserts, which ensure the prolonged availability of fresh fruit in the market from May to November. Climate conditions, soil types and production technology are the main factors that give table grapes the ability to grow all over the country. ‘Thompson Seedless’ and ‘Flame Seedless’ dominate the production as they remain the most popular varieties in the European Union markets, the major importer of the Egyptian grapes; however, producers are expanding towards other varieties including ‘Early Superior’, ‘Superior’, ‘Roomy’ and ‘Crimson Seedless’ to supply other markets such as Argentina and New Zealand (Omar, 2020).

‘Crimson Seedless’ is a vigorous cultivar with five to six non-fruiting basal buds, classified as a mid- to late-season maturing grape based on weather conditions (mid-September to mid-November in the northern hemisphere). Similar to most grape cultivars, ‘Crimson Seedless’ is classified as moderately resistant to drought and salinity conditions (Dokoozlian et al., 2016). The berries are bright red, large, have a pit characterised by a cylindrical-oval shape and are seedless. They have a high nutritional value, and are not highly susceptible to early or late season cracking. A primary factor driving the growth of this variety is the high retail demand (Dokoozlian et al., 2016); however, cluster weight and shape, berry size, soluble solid contents:titratable acidity ratio (SSC/TA ratio), aroma and colour are all factors that influence overall fruit quality (García-Pastor et al., 2020).

Failure to develop adequate red colour at maturity is a common issue associated with ‘Crimson Seedless’ grape, especially in warm and humid conditions of the semi-arid climates (Spayed et al., 2002; Abd El-Rahman et al., 2018). In Egypt, most growers of ‘Crimson Seedless’ grape irrigate their vineyards well to ensure adequate water supply (≈4,500–5,000 m³ · ha^–1) that satisfies the maximum field capacity (≈0.328 m³ · m^–3) during the ripening stage due to hot summer (mid-July to late-August); however, they experience poor berry colour and low sugar contents (El-Ansary, 2017; Temnani et al., 2021). Most clusters usually show variability in berry colour, which leads to depreciation of their market value (Cantín et al., 2007; Lurie et al., 2010; El-Sayed, 2013). In many commercial ‘Crimson Seedless’ vineyards of clay soils and traditional surface irrigation, adequate water in root zone may lead to an enhanced fruit set that could potentially restrict berry growth and results in tightly filled and compact clusters, which become more susceptible to bunch rots, in addition to poor colour and taste quality. These problems could be overcome with proper cultural practices such as trunk girdling and ethephon foliar application (Dokoozlian et al., 1995), gibberellic acid foliar application (Dokoozlian, 2001), ABA foliar application (Ferrara et al., 2013), combined ABA and sucrose foliar application (Ferrara et al., 2015), shoot thinning (Dokoozlian et al., 2016) and deficit irrigation (Pinillos et al., 2016; El-Ansary, 2017; Temnani et al., 2021). In this regard, this research is pointing out to vineyards in clay soils that are still subjected to surface (also known as flood or furrow) irrigation. It is not the most efficient irrigation method, since it uses more amount of water and water loss is higher compared to new irrigation methods, but it is cheap (USGS, 2018).

It is well known that clay soils are less permeable than other soil types. This indicates the absence of natural drainage, and consequently with continuous irrigation, the soil will suffer from waterlogging conditions. Waterlogging is more prolonged and more severe in heavy textured soils, and it is associated with temporary aeration stress, particularly with higher levels of groundwater table, which indirectly affects plant growth and fruit quality (Yadav et al., 2013). Waterlogging and salinisation of soils are common problems associated with flood irrigation, especially in the arid and semi-arid conditions. The greater the aridity of the region, the larger the quantity of irrigation water used, and the result of such water-intensive irrigation practice is an eventual increase in waterlogging and concentrate salts, drawn up from lower in the soil profile, in the plants’ root zone. In addition, the rivers in arid and semi-arid regions tend to become progressively saline from their headwaters to their mouths, and excess salinity within the root zone reduces plant growth, particularly with the small rainfall percentage that is not enough to leach away the accumulated salts. Therefore, adequate drainage system could solve soil-related problems. Waterlogging can also be minimised using the micro-irrigation techniques that apply water more precisely and easily limit quantities to no more than the plant needs (FAO, 1997). In Egypt, for example, the Nile River is the main water resource, and the installation of good drainage systems or the use of new irrigation techniques in some small-scale farming activities would be somewhat expensive (Agricultural Statistics of Egypt, 2014). This was a reason to look for other agricultural practices that improve grapevine growth, productivity and fruit quality.

All agronomic practices that influence the canopy microclimate and the grape yield to leaf area ratio may influence the berry primary and secondary metabolites (Tardaguila et al., 2008; Gambacorta et al., 2011; Baiano et al., 2015; Suriano et al., 2016; Tarricone et al., 2017). Basal defoliation (BD), the practice of leaf removal in the cluster zone, is one of the most widely used canopy management techniques applied to modify fruit-zone microclimates, and the impact of the timing and intensity differs across varieties and climates. This practice regulates yield components in high-yielding cultivars via reduced fruit set percentage when performed immediately before anthesis (Poni et al., 2006; Intrieri et al., 2008; Sabbatini and Howell, 2010). This procedure eventually affects vine carbohydrate supply by reducing carbohydrates in the flowers at anthesis (altering source: sink ratio) (Petrie et al., 2003; Vasconcelos et al., 2009) or by altering the canopy microclimate to increase fruit exposure to sunlight and improve air penetration into the clusters (Austin and Wilcox, 2011). Early defoliation in vigorous grapevines noticeably affected vine performance, and thus reduced cluster compactness, weight and yield, lowered the incidence of Botrytis bunch rot and improved fruit composition (Tardaguila et al., 2010; Yorgos et al., 2012; Beslic et al., 2013; Diego et al., 2014; Sabbatini, 2015; Acimovic et al., 2016; Intrieri et al., 2016; Frioni et al., 2017; Shalan and Hamza, 2020). Similar results were reported when defoliation was performed at full-bloom stage, but without a reduction in yield (Sivilotti et al., 2016). Late BD applied at the pea-size stage reduced fruit soluble solids and sugar contents, and decreased acidity as a consequence of faster rate of malic acid catabolism (Petrie et al., 2003). Late defoliation applied by the beginning of berry colouring (veraison stage) showed an incidence of sunburn with a negative effect on the biosynthesis of anthocyanins, and thus berry colour (Mosetti et al., 2016). Basal defoliation is widely used in cool climates, characterised by low solar heat accumulation and high air humidity and rainfall (Frioni et al., 2017). Such conditions can increase polyphenols and anthocyanins up to 18% due to better UV radiation in the cluster zone that may positively affect phenol synthesis by stressing the berry skin (Šuklje et al., 2014).

Anthocyanins are water-soluble vacuolar pigments that belong to the flavonoids group and are responsible for grape colour (García-Beneytez et al., 2002). In ‘Crimson Seedless’ grape, these pigments accumulate during the ‘veraison’ stage, which represents the beginning of the ripening process (Cantín et al., 2007). In general, most table grapes grown in warm climates have less red colour than those grown in cold climates (Spayed et al., 2002). The increase in interior canopy leaves results in lack of light penetration, and thus leaf removal is considered an important canopy practice (Tarricone et al., 2017). Defoliation is considered one of the main factors affecting the accumulation of anthocyanins (Downey et al., 2006) through changes in microclimate temperature, humidity, wind speed and leaf wetness around the clusters (English et al., 1990). Clusters exposed to sunlight had higher sugars, anthocyanins and phenols, while acidity was lower when compared to the shaded clusters (Diago et al., 2012; USGS, 2018). Possible negative effects of leaf removal are reduction in leaf area per vine and berry weight, decrease in total acidity due to reduction in malic acid content, and decrease in bud differentiation in the following season (Lemut et al., 2013; Mosetti et al., 2016). Substantial BD of more than six leaves has not been thoroughly evaluated (Verdenal et al., 2018; Tarricone et al., 2020).

Salicylic acid (SA), 2-hydroxybenzoic acid (C₇H₆O₃, molecular weight = 138.121 g · mol^–1), a phenolic compound, natural growth regulator and antioxidant in vascular plants, stimulates many physiological processes that regulate plant growth and development such as nutrient uptakes, membrane permeability, enzyme activities, photosynthesis capacity, stomatal conductance and transpiration under various biotic and abiotic stresses (Hayat et al., 2010; Rady et al., 2015; Rady et al., 2017). It is an important secondary metabolite in grapes that activates the expression of several defence-related genes (Loake and Grant, 2007), and effectively improves berry colour, flavour, astringency, bitterness, size and weight, and delays softening through inhibiting the activity of cell wall degrading enzymes such as cellulase, polygalacturonase and xylanase (Srivastava and Dwivedi, 2000; Zhang et al., 2003), suggesting that SA has an anti-senescent effect (Harindra Champa et al., 2015). Application of SA to ‘Sahebi’ grapes at pre-veraison stage increased total phenol, flavonoid and anthocyanin contents (Oraei et al., 2019).

Cyanocobalamin (CCA) is the manufactured version of cobalamin, also known as vitamin B₁₂ (C₆₃H₈₈CoN₁₄O₁₄P, molecular weight = 1 355.38 g · mol^–1), a water-soluble vitamin that is naturally found in animal cells. It is not synthesised by plant cells, but it was found to accumulate within plant cell organs such as cytosol, plastids and mitochondria, providing definitive evidence that some plants can absorb and transport cobalamin (Roje, 2007; Asensi-Fabado and Munne-Bosch, 2010; Lawrence et al., 2018) that was synthesised by some microorganisms (e.g. archaea, bacteria, fungi) that live in the plant root zone through microbial interaction (Antony, 2018). Cobalamin is a cobalt-containing tetrapyrrole cofactor involved in intramolecular rearrangement, and necessary for the regulation of DNA synthesis during plant cell division (Smith et al., 2007; Ferrer et al., 2016). It plays a vital role in the conversion of homocysteine to methionine (Allen, 2012), which is a precursor for a variety of metabolic processes in plants, including polyamine, protein and ethylene synthesis. Methionine synthase is required for methionine biosynthesis, and it serves as a link between the methionine biosynthesis pathway and the one-carbon cycle pathway related to photosynthesis capacity (Zeh et al., 2002; Fontecave et al., 2004). Cobalamin has been suggested to be an intercellular antioxidant that reduces the levels of intercellular reactive oxygen species (ROS) and molecule damages (e.g. DNA, RNA, proteins, lipids, enzyme cofactors), and improves overall cell physiology stimulating the growth and survival of cells exposed to extremely oxidative environmental stresses (Jones et al., 2013; Ferrer et al., 2016; Vasquez et al., 2022). Cyanocobalamin has been used to improve fruit colour and other quality attributes of kaki (Lo’ay, 2010), ‘Thompson Seedless’ grapes (Lo’ay, 2011), mango (Samaan et al., 2011), guava (Samaan et al., 2012), banana (El-Baz et al., 2016) and ‘Le Conte’ pear (Abd El-Bary et al., 2017).

Due to limited research on clay-soil grown ‘Crimson Seedless’ grapevines that demonstrate quality problems under flood irrigation in semi-arid conditions, and in an attempt to use some efficient cultural practices, instead of commonly used methods such as trunk girdling and foliar spray of ethephon (Dokoozlian et al., 1995), mechanical cluster thinning (Tardaguila et al., 2008), foliar spray of ABA (Lurie et al., 2010), cover cropping and deficit irrigation (Gambacorta et al., 2011), leaf removal in the cluster area along with the East and West geographical directions (Baiano et al., 2015) and moderate deficit irrigation (Tarricone et al., 2017) that did not show that much improvement in vine growth or fruit quality under such conditions, this research aimed to determine whether the combined application of BD with either SA or CCA could be used as a new sustainable solution that would meet the growers’ concerns on this cultivar. Most of the previous reports have focussed on the role of BD by itself, as well as the solo role of foliarly sprayed SA or CCA on the growth and productivity of different fruit trees, including grapes. In this regard, the present research is considered the first to study the combined role of BD with either SA or CCA on the growth, productivity and fruit quality of ‘Crimson Seedless’ grapevines grown under the semi-arid Mediterranean climate of Egypt. It is also noteworthy that this study is comparing the effective roles of two stress-reducing substances (SA and CCA) in terms of price and nature. The cheap price of SA [≈$52 · 500 g^–1] (Sigma Aldrich, St. Louis, MO, USA) in Egypt, in conjunction with its natural origin, makes it a favourable cultural practice to the growers, compared to CCA that has a synthetic origin and a higher price [≈$121 · 1 g^–1] (Sigma Aldrich, St. Louis, MO, USA), although it was reported safe for human use.

Under the Egyptian semi-arid Mediterranean climate and flood irrigation conditions, clay-soil grown ‘Crimson Seedless’ grapevines manifested poor fruit quality (i.e. compact clusters, pale colour, low sugars, high acidity), which means low-grade fruit during marketing (Spayed et al., 2002; Cantín et al., 2007; El-Sayed, 2013; El-Ansary, 2017; Abd El-Rahman et al., 2018). This present study aimed to understand whether the combined application of BD with either SA or CCA would solve the growers’ concerns on this cultivar. Results indicated that ‘Crimson Seedless’ grapevines treated with either BDPB or BDFB, along with foliarly sprayed SA (T3 and T6, respectively), showed a positive enhancement in plant growth parameters (i.e. shoot length, leaf area) (Figure 2), whereas the photosynthesis markers (i.e. chlorophyll and carbohydrate contents) were more affected by T3 in both seasons (Figure 3). It was reported that leaf removal resulted in enhanced chlorophyll and carbohydrate contents by the end of the growing season to compensate the increased levels of photosynthesis and respiration in the remaining leaves, so that plants can mitigate the impacts of leaf removal (Petrie et al., 2003; Palliotti et al., 2011). Leaf removal has also been reported to increase the supply of water, nutrients and hormones from the roots to the developing leaves, leading to more new flushes with highly efficient tissues (Tardaguila et al., 2010; Palliotti et al., 2011), which eventually affect overall plant growth (Figure 2), productivity (Figure 4) and fruit physiochemical characteristics (Figures 5–9). Previous findings reported a positive role of SA or CCA on total chlorophyll content of ‘Bez El-Naka’ grapes (Abdel-Salam, 2016) and ‘Le Conte’ pear (Abd El-Bary, 2017), respectively. It was reported that SA improved plant height, chlorophyll content (Ghasemi et al., 2016), net photosynthesis and carbohydrate accumulation of heat-stressed grapevines (Wang et al., 2010). Also, CCA induced the antioxidant capacity, inhibited lipid peroxidation and enhanced the biosynthesis of chlorophyll and carotenoids in salt-stressed common bean plants (Keshavarz and Moghadam, 2017).

The reduction in berry set percentage with BD has shown to be overcome and led to the maximum yield per vine with the application of either SA or CCA, with best results achieved with SA at either BDPB (T3) or BDFB (T6) (Figure 4). This was also represented with enhanced cluster weight, along with less compactness (Figure 5), as well as average berry weight, particularly with T3 (Figure 6). Berry firmness has shown similar responses to SA and CCA, with best results at BDPB (T3 and T4, respectively) in both seasons (Figure 6). In this context and regardless of the stage, BD has led to lack of carbohydrates, which in turn reduced the percentage of fruit set, and hence resulted in loose clusters (Poni et al., 2006; Intrieri et al., 2008; Tardaguila et al., 2010). It was reported that the carbohydrate supply at bloom stage is the major factor affecting fruit set (Caspari and Lang, 1996). Reduced carbohydrate supply during the phenological stages of flowering and fruit set has resulted in early abortion, and hence reduced percentage of berry set (Poni et al., 2005; Intrieri et al., 2008). Basal defoliation at the PB stage has been shown to reduce the photosynthates supply to flowers, resulting in reduced berry set (Caspari et al., 1998). This could explain the slight reduction in fruit set percentage and cluster compactness with improved yield when applying BDPB, compared to BDFB (Figure 4 and Figure 5), as also previously reported on ‘Crimson’, ‘Tempranillo’, ‘Grenache’ and ‘Carignan’ grapes (Diago et al., 2010; Tardaguila et al., 2010; Shalan and Hamza, 2020). It was reported that severe defoliation resulted in fewer number of berries, and hence less compacted clusters in ‘Merlot’ grapes (Yorgos et al., 2012). In addition, BD during the flowering stage has reduced the number of berries per cluster, and hence clusters’ compactness, without affecting the next season’s bud fertility in ‘Cabernet Sauvignon’ and ‘Prokupac’ grapes (Beslic et al., 2013). Defoliation before or during the flowering stage reduced cluster compactness, compared to that performed during fruit set stage (Diego et al., 2014). Defoliation during bloom or fruit set stages resulted in considerably fewer number of berries per cluster, which altered the cluster form and reduced compactness (Sabbatini, 2015; Sternad et al., 2015; Acimovic et al., 2016). The findings of the present study are inconsistent with the previous reports on ‘Crimson Seedless’ grapes that showed a positive improvement in cluster weight and size, as well as berry weight and size when defoliation was performed before the flowering stage (BDPB); however, the present results confirmed the role of BDPB on berry firmness (T2 vs T5) (Figure 6) as being in conformity with that elucidated in previous reports (Abd El-Razek et al., 2010; Tardaguila et al., 2010). Removing 30% of the leaf area with some shoots and inflorescences led to fewer berries per cluster, and thus less compacted clusters and firmer berries with less vulnerability to decays (Intrieri et al., 2016).

As a phytohormone, SA regulates the physiological and biochemical processes, improves chlorophyll content, photosynthesis, total carbohydrates and hence plant growth, flowering, setting, productivity and fruit quality of various crops, including grapes (Hayat et al., 2010; Abdel-Salam, 2016; Farhood et al., 2016; Ali et al., 2017; Roustakhiz and Saboki, 2017; Abou-zaid and Badawy, 2018; Ghattas, 2020). Preharvest application of SA has been reported to improve antioxidant levels, colour and yield in low-pigmented ‘Magenta’ and ‘Crimson Seedless’ grapes, and preserve quality traits during storage (García-Pastor et al., 2020). Berry firmness is one of the most critical physical quality criteria in determining customer acceptance (Poni et al., 2018). The nature of cell wall, water content and turgor pressure play a vital role in berry firmness (Payasi et al., 2009). Results indicated that BDPB positively improved berry firmness compared to BDFB (Figure 6). The combined application of BDPB with either SA (T3) or CCA (T4) similarly improved berry firmness, compared to the solo application of BDPB (T2). The effect of SA or CCA could be due to their antioxidant roles, which preserve insoluble pectin contents, inhibit the activity of primary cell wall degrading enzymes such as xylanase, cellulose and polygalacturonase, and stimulate cell division and enlargement (Eichel et al., 1995; Hayat et al., 2010), thus preserving berry firmness. It was reported that SA effectively maintained fruit firmness (Ennab et al., 2020) due to its anti-senescent role that resulted in reduced endogenous ethylene production (Nissen, 1994), hence protecting cell wall structure (Kazemi et al., 2011) and maintaining cell turgor pressure through the accumulation of defence-related metabolites (Zhu et al., 2016), including a salicylate-dependent pathway, resveratrol synthesis and cell-wall strengthening components (Serrano et al., 2017). Salicylic acid was also reported to improve plant antioxidant capacity and prevent cell-wall degradation through its positive effect on phenols and antioxidant enzymes (Cui et al., 2020). It was also suggested that CCA effectively increased cell wall polysaccharides during berry development (Lo’ay, 2010). Cyanocobalamin is an intercellular antioxidant that reduces the levels of intercellular ROS and molecule damages (e.g. cell wall lipids, enzyme cofactors) (Jones et al., 2013; Ferrer et al., 2016; Ghasemi et al., 2016; Vasquez et al., 2022), which could also be the reason for maintaining cell wall integrity, and hence overall berry firmness, as previously reported in ‘Thompson Seedless’ grapes (Lo’ay, 2011) and ‘Le Conte’ pear (Abd El-Bary, 2017). Cyanocobalamin also plays a role in methionine biosynthesis (Ferrer et al., 2016), which is a precursor of polyamines synthesis (Zeh et al., 2002) that was reported to maintain cell turgor pressure and improve berry firmness (Mirdehghan and Rahimi, 2016).

Berry colour characteristics indicated a positive role of CCA over SA, in combination with either BDPB (T4) or BDFB (T7) (Figure 7). However, the difference between T4 and T7 was insignificant for all colour characteristics, except for anthocyanins in both seasons (Figure 7). Improved colour of ‘Crimson Seedless’ grapes was represented by the improved anthocyanins and colour lightness (L*), but decreased values of hue angles (Figure 7), which negatively correlate with colour development, as previously confirmed (Ruiz et al., 2005; Elmenofy et al., 2021). Anthocyanins are the main pigment responsible for berry colour in ‘Crimson Seedless’ grapes (García-Beneytez et al., 2002). The higher the anthocyanin contents, the redder the colour of the berries were (Figure 7), and this could be attributed to the role of CCA in activating the cDNA and cobalamin-independent methionine synthase during berry development (Ali et al., 2017) that plays a vital role in methionine biosynthesis (Allen, 2012), which is the precursor of polyamine, protein and ethylene synthesis (Boselli et al., 2019). Methionine synthase has also a role in the one-carbon cycle pathway related to photosynthesis capacity (Zeh et al., 2002; Fontecave et al., 2004) and the biosynthesis of polysaccharides (Krook et al., 2000), and other secondary metabolites such as phenolic compounds, particularly flavonoids (i.e. flavonols, flavones and anthocyanins) (Ni et al., 2020). Anthocyanins are synthesised via the flavonoid pathway (He et al., 2010), and there are different types of anthocyanins that differ in their colours based on the cellular pH, such as malvidin (purple-red), delphinidin (pink), peonidin (purple-blue), cyanidin (red) and petunidin (purple) (García-Beneytez et al., 2002). Anthocyanins accumulation is also affected by environmental conditions such as light (i.e. photoperiod, intensity, composition in wavelengths of the light spectrum) that play an important role in the expression of genes along the flavonoid pathway, and related transcription factors that regulate the accumulation of anthocyanins in grape berries (Koyama et al., 2012; Kondo et al., 2014; Zoratti et al., 2014; Cheng et al., 2015). High temperature also inhibits anthocyanins accumulation, whereas lower temperature enhances the expression of flavonoid pathway genes (Ubi et al., 2006; Lin-Wang et al., 2011; Kuhn et al., 2014). It was noticed that CCA improved fruit colour via increased accumulation of peonidin and acylated derivatives of anthocyanins in grape peel (González-Neves et al., 2005). Salicylic acid was not as highly effective as CCA on fruit colour (Figure 7), and this could be related to the role of SA in delaying fruit maturity via the inhibition of ethylene biosynthesis, as well as its relationship with other phytohormones that affect overall plant metabolism (Arif et al., 2020). There is a positive role of CCA on methionine biosynthesis (Allen, 2012), which is the precursor of ethylene biosynthesis (Zeh et al., 2002; Fontecave et al., 2004). Both ethylene and abscisic acid (ABA) are commonly recognised to act antagonistically in the control of plant growth and development (Wright, 1980; Li et al., 2011). However, several studies on ethylene and ABA suggested that they can operate in parallel or even interact positively (Luo et al., 2014; Li et al., 2019), and this could justify the colour improvement in CCA-treated plants, compared to SA-treated plants (data not shown), since ABA is primarily responsible of the accumulation of anthocyanins and colour development in grapes (Ban et al., 2003).

The combined application of BDPB and CCA (T4) was also the most effective on berry SSC, TA, SSC/TA ratio and total sugars; however, this effect was followed by similar effects for both T3 and T7 (Figure 8). Phenols are one of the most important groups of secondary metabolites in plants that act as antioxidants, which protect cell structure and improve plant tolerance against stress (Boud, 2007). They also have been shown to be the major influence on the sensory quality of the fruit (i.e. colour, flavour, taste) (Balasundram et al., 2006). Anthocyanins are the prominent phenolic compounds responsible for berry colour, and contribute to the plant antioxidant capacity more than any other phenolic compounds (Mazza, 1995; Winkel-Shirley, 2001; Koes et al., 2005; Kristl et al., 2011). In addition, anthocyanins can offer slight astringency to the taste of the grapes, and can interact with some aroma substances (Dufour and Sauvaitre, 2000; Vidal et al., 2004a; Vidal et al., 2004b). The most pronounced effect on phenols was recorded for T4, followed by a similar effect for both T3 and T7 (Figure 9), which confirm the positive role of BDPB over BDFB. In general, this could be attributed to enhanced light penetration within the vine due to leaf removal, associated with stimulated root and shoot growth, along with improved water uptake, which in turn led to an enhanced level of photosynthesis and carbohydrate accumulation (Hunter and Le Roux, 1992; Tardaguila et al., 2010; Intrieri et al., 2016; Shaker, 2016). Previous reports have shown that leaf removal resulted in increased levels of solar radiation on both canopy and clusters, which effectively improved the following characteristics of berry contents: SSC/TA ratio, sugars, anthocyanins and phenols (Bergqvist et al., 2001; Poni et al., 2006; Poni et al., 2009; Tardaguila et al., 2010; Diago et al., 2012; Sun et al., 2012). Previous findings have also confirmed that BDPB plays a positive role in accelerating the ripening process, and that in the case of ‘Crimson Seedless’ grapes, suitable application of this technique further contributes to an improved SSC/TA ratio, anthocyanins and phenols (Poni et al., 2005; Tardaguila et al., 2010; Yorgos et al., 2012; Beslic et al., 2013), particularly with four-leaf BD (Shalan and Hamza, 2020). The solo application of CCA was reported to improve ‘Crimson Seedless’ grapes’ berry contents of SSC, sugars, anthocyanins and phenols (Lo’ay, 2017). Similarly, CCA improved fruit set, SSC, TA and SSC/TA ratio in ‘Le Conte’ pear (Abd El-Bary, 2017). The role of SA in the enhancement of berry chemical characteristics could be ascribed to its positive effect on leaf area, chlorophyll content, photosynthesis capacity and carbohydrate contents (Abd El-Razek et al, 2010; Diago et al., 2010; Hayat et al., 2010). Preharvest spray of SA induced berry ripening, which was evidenced by improved SSC/TA ratio, total phenols (Champa et al., 2015; Abdel-Salam, 2016) and anthocyanins (García-Pastor et al., 2020), whereas the application at pre-veraison stage increased total phenols, flavonoids and anthocyanins, particularly malvidin-3-glucoside at harvest (Oraei et al., 2019).

The inflicted fruit quality of ‘Crimson Seedless’ grapevines grown under the conditions of heavy clay soils, flood irrigation and semi-arid climate could be related to improper physiological and biochemical processes that were expressed by reduced vegetative growth, photosynthesis rate, productivity and hence fruit quality. Under such growing conditions, the sole use of BD or its use in combination with FS of either SA (200 mg · L^–1) or CCA (20 mg · L^–1) was found beneficial for improving overall plant growth and productivity. The improved shoot length and leaf area that were obtained pursuant to the use of BD treatments enhanced light penetration within the vine, and hence photosynthesis activity and carbohydrate accumulation. This effect was reflected on total yield and fruit quality, and definitely increased when SA or CCA was combined with the BDPB or BDFB stages. The most pronounced effect on vegetative growth, photosynthesis activity, cluster and berry weight and dimensions, and total productivity was mainly observed in the case of BDPB+SA (T3). Berry firmness, colour and sensory characteristics were more related to BDPB+CCA (T4). Both treatments could be suggested as proper applications to improve the quality of ‘Crimson Seedless’ grape crop subjected to flood irrigation under semi-arid conditions. Future research could incorporate the use of BDPB, SA and CCA as one application to compensate for the reduction in some quality characteristics attributable to the sole use of each treatment. More research is also needed: (i) to determine whether the low berry quality (and resultant poor marketability) observed in ‘Crimson Seedless’ grapes cultivated under the aforementioned growing conditions could be attributed to partially stressed vines; and (ii) to enhance vine growth and berry characteristics, particularly given the fact of reduced amounts of irrigation water, since water scarcity is, of late, becoming a problem in Egypt, and may become a limiting factor for the overall fruit industry in the future.