Effect of Rootstock Selection on Tree Growth, Yield, and Fruit Quality of Lemon Varieties Cultivated in Greece

Abstract

Lemon is a prominent citrus fruit that supports regional economies worldwide. Several agronomic and fruit quality attributes are affected by the rootstock selection, thus its selection is essential for a successful grove. This study aims to compare the agronomic and quality attributes of four lemon cultivars (‘Mikrokarpo Messaras’, ‘Nouvel Athos’, ‘Femminello Commune,’ and ‘Zia gara Bianca’) grafted onto three rootstocks (‘Sour Orange’, ‘Yuma Ponderosa lemon’, and ‘Volkameriana’). The yield and rootstock/scion ratio were estimated along with fruit morphological characteristics (size, equatorial, and polar diameter). Internal fruit quality was also estimated (total soluble solids, total acidity, juiciness, ascorbic acid, total phenols, and total antioxidant activity). ‘Volkameriana’ rootstock stood out among the studied rootstocks, as all grafted lemon varieties increased their productivity. Its combination with the Italian cultivar ‘Femminello Commune’ exhibited enhanced tree vigor and tree yield. For all studied cultivars, the use of ‘Volkameriana’ or ‘Yuma Ponderosa lemon’ rootstocks decreased the total soluble content and total acidity, increased the ascorbic acid content, and did not influence the TSS/TA ratio, total phenols or total antioxidant activity. In conclusion, the vigorous ‘Volkameriana’ and ‘Yuma Ponderosa lemon’ rootstocks are a promising replacement for ‘sour orange’. This research provides valuable insights into the potential use of ‘Yuma Ponderosa lemon’ as a rootstock for lemons, as existing literature is rather limited.

1. Introduction

The lemon (Citrus limon (L.) Burm. F) holds a significant position among citrus fruits globally, ranking third after oranges and mandarin–tangerines, owing to its unique nutritional, phytochemical, nutraceutical, and industrial uses [1,2]. Although lemons are distributed worldwide, they thrive best in regions with warm, frost-free climates due to their cold sensitivity. In the Mediterranean region, Spain and Italy dominate lemon production, contributing to approximately 80% of the total fruit output, while Greece and Portugal’s contribution stands at only 7% [1]. In Greece, lemon cultivation covered approximately 3540 hectares in 2021, producing 85.630 tons of lemon fruit [1]. The majority of lemon groves are concentrated in the northern part of the Peloponnese peninsula, with a few areas cultivated in Crete. Key varieties include the local ‘Maglino’ and the Italian ‘Fem mi nello Commune’ and ‘Interdonato’, which comprise nearly 80% of the total lemon cultiva tion area in Greece. In the warmer South regions of Greece (Crete), the cultivars ‘Ziagara Bianca’ (a clonal selection of ‘Femminello’), and the indigenous cultivar ‘Mikrokarpo Messaras’ are also cultivated.

In terms of fruiting seasons, ‘Femminello Commune’, ‘Ziagara Bianca’, and the Georgian variety ‘Nouvel Athos’ are late-winter-to-early-spring varieties, while the local Greek variety ‘Mikrokarpo Messaras’ is an early autumn variety. The latter variety is characterized by its excellent drought and heat tolerance, albeit with a smaller lemon fruit size. Notably, the Georgian variety ‘Nouvel Athos’ exhibits slightly higher cold hardiness compared to other known lemon varieties cultivated in Greece, particularly when grafted onto ‘Volkameriana’ (Citrus volkameriana Ten. and Pasq.) rootstock.

Rootstock choice is a critical decision during citrus grove establishment, as it directly impacts the external and internal attributes of the scion [3]. Numerous studies highlight the fact that rootstock selection significantly affects agronomic (tree growth, flower development, and fruit yield), morphological (size, fruit shape, and weight), and qualitative attributes (total soluble solids, total acidity, ascorbic acid, juice content, and total phenolics and antioxidants) of citrus fruits [4,5,6]. Towards a successful citriculture, rootstock choice plays a pivotal role in the economic viability of citrus groves [7]. The use of appropriate rootstocks enables producers to cope with environmental and soil-borne challenges, as well as mitigate threats from diseases like citrus tristeza virus (CTV), other viroids, and Phytophthora [8]. Consequently, the careful selection of scion/rootstock combinations in lemon cultivation holds paramount importance for establishing economically profitable plantations [5].

In Greece, the most commonly used rootstock for citrus plantations is ‘sour orange’ (Citrus aurantium L.), followed by ‘Swingle Citrumelo’ (Citrus paradisi × Poncirus trifoliata), ‘Carrizo Citrange’ (Citrus sinensis × Poncirus trifoliata), ‘Poncirus trifoliata’, and ‘Volkameriana’ [9]. Also, there is little information regarding the impact of the use of vigorous rootstocks in lemon cultivation as a means to increase yield and fruit quality attributes [10]. ‘Volkameriana’, a natural hybrid of mandarin × citron of Italian origin [11], proves to be adaptable to various soil types, including sandy soils with high pH values, and exhibits tolerance to high salinity [9]. Additionally, it facilitates rapid growth of the scion and ensures high and early yields [12]. Another rootstock used is ‘Yuma Ponderosa lemon’ (Citrus limon (L.) Burm. F.), a pommelo hybrid [13] known for its tolerance to CTV and Phytophthora parasitica, but susceptibility to gummosis and nematodes [13]. It is recommended for lemons grown in well-drained soils [13].

As lemon cultivation in Greece continues to expand [1], there is limited knowledge about alternative rootstock options apart from ‘sour orange’. This study aimed to evaluate the impact of three rootstocks (‘sour orange’, ‘Volkameriana’, and ‘Yuma Ponderosa lemon’) on four lemon varieties, one Greek (‘Mikrokarpo Messaras’), one Georgian (‘Nouvel Athos’), as well as two Italian accessions (‘Femminello Commune’ and ‘Ziagara Bianca’). The assessment focused on tree characteristics and fruit quality attributes. The ultimate objective was to identify a rootstock that could match, or even surpass, ‘sour orange’ in terms of fruit quality and, potentially, replace it in lemon cultivation.

2. Materials and Methods

2.1. Plant Material and Sampling

In the current study, four commercial lemon varieties (‘Femminello Commune’, ‘Ziagara Bianca’, ‘Nouvel Athos’, and ‘Mikrokarpo Messaras’), which are cultivated in Greece, grafted upon three different rootstocks (‘sour orange’—medium vigor, ‘Yuma Ponderosa lemon’—high vigor, and ‘Volkameriana’—high vigor) were used. The trees were planted in 2012, when they were 2 years old, at a location called Agia in Chania—Crete, Greece, (35°28′25″ N, 23°56′17″ E, 52 m altitude)—in the same commercial lemon grove. The experimental design was a randomized complete block, with three replications for every cultivar/rootstock combination, for agronomic and quality attributes.

In Crete, the climate is characterized as Mediterranean, with hot and dry summer (38–42 °C) followed by mild winter (2–5 °C). In the current experiment, tree spacing was 4 m × 6 m. The soil of the citrus grove was sandy loam, well-drained with pH 6.7, and contained 2.1% of CaCO₃. All trees received the same cultivation practices, were irrigated via drip irrigation from May until October with irrigation water of low Na⁺, Co⁻, and B⁻ ions content, with 0.68 mMhos and fertilized with 21-0-0, 0-20-0, and 0-0-50, which each contains 0.01, 0.06, and 0.1 units of N, P, and K respectively.

The fruits of the variety ‘Mikrokarpo Messaras’ were harvested annually (2019–2022) during October, while the fruits from the other three varieties (‘Femminello Commune’, ‘Ziagara Bianca’, and ‘Nouvel Athos’) were harvested during January, once they reached maturity. Great attention was given to harvesting only the fruits produced by the principal bloom and from trees that were in optimal sanitary condition. A sufficient quantity of lemons was carefully hand-picked using pruning scissors. For each scion/rootstock combination (n = 5), a total of 20 fruits were collected from 5 trees, resulting in a total of 100 lemons. All parts of the tree, including the internal and external sections, were harvested from all four orientations of the tree crown.

2.2. Scion/Rootstock Ratio and Tree Yield

The scion and rootstock circumference were measured only in December 2022, just 15 cm above and below the bud union, and their ratio was calculated by dividing the scion diameter by the rootstock diameter. The circumference was measured with a measuring tape. Annual yields were recorded for each tree for 3 years (2019–2022). From all trees which participate in the experiment, all fruit were harvested and weighed to record tree yield. The weight of each fruit was estimated using a weighing scale (model 572, Kern & Sohn Gmbh, Balingen, Germany).

2.3. Morphological Characterization and Fruit Mass

Analyses were conducted on 10 fruits stored at room temperature on the day of harvest, for each replication for each scion/rootstock studied combination. The equatorial diameter (ED) and polar diameter (PD), were measured using a digital vernier caliper (150 mm, Parkside, Donaueschingen, Germany). The ratio between the ED and PD (E/P) conveys the fruit’s shape where lower values show a rounder shape of fruit and higher values declare a more elongated shape. The fruit mass was estimated as previously reported, via the use of a weighing scale.

2.4. Qualitative Fruit Characterization

The qualitative attributes were estimated on 10 fruits per replication, for each scion/rootstock studied combination. All measurements were performed at room temperature. The rind thickness (RT) was measured at two equidistant and opposite points of the fruit after it was horizontally split at the point of the equator using the digital vernier caliper, as previously reported. Seeds were manually extracted from the fruit and visually counted. To estimate the juice content, five fruits were weighed and cut along their equatorial zones, and the juice was extracted using a commercial manual juice extractor. The equation % juice content = (JM/FM) × 100, (JM: juice mass (g), and FM: fruit mass (g) was used to calculate the juice content, which was expressed as the percentage of total fruit weight. The same juice was immediately centrifuged at 1.650× g for 15 min at 4 °C. Total soluble solids (TSS) and total acidity (TA) were measured immediately via the use of the PAL-BX/ACID 1 Master Kit (ATAGO Co. Ltd., Tokyo, Japan) and expressed as °Brix and % citric acid, respectively, according to the manual instructions [14]. The lemon fruit TSS/TA ratio was calculated.

The quantification of ascorbic acid was performed according to the AOAC method. Briefly, 1 mL of centrifuged lemon juice sample was mixed with 1 mL of extraction solution (HPO₃-acetic acid). Titration with 2,6-dichlorophenolindophenol sodium salt hydrate (2,6-DCPI) was performed to estimate the acid content of the lemon juice. The results were expressed as mg ascorbic acid 100 mL⁻¹ juice.

2.5. Total Phenolic Content and Antioxidant Capacity

Total phenolic content (TP) was determined according to [15]. In detail, the phenolic compounds were extracted by mixing 1 mL juice sample with 9 mL 80% (v/v) methanol. The mixture was incubated for 24 h at 4 °C while being stirred every 12 h. Afterward, the mixture was centrifuged at 4 °C for 15 min at 5.000 rpm. An aliquot of the supernatant was used in order to determine the total phenolic content via the Folin–Ciocalteu colorimetric assay. Total phenolics were estimated spectrophotometrically at 760 nm (UV-1900i, Shimadzu, Kyoto, Japan). The results were expressed as gallic acid equivalent (GAE) (mg GAE 100 mL⁻¹ juice).

The antioxidant capacity of the juice was estimated according to [16] with some modifications. In order to perform the assay, fresh FRAP reagent solution (300 mM sodium acetate buffer, pH 3.6, 10 mM Fe (II)-TPTZ prepared in 40 mM HCl, 20 mM FeCl₃·H₂O (10:1:1)) was prepared prior to every analysis. An aliquot of the juice supernatant was mixed with the FRAP reagent, the mixture was incubated for 30 min at 37 °C water bath, and the absorbance was measured afterwards at 593 nm. The ascorbic acid solution was used to express the antioxidant capacity as mmol Trolox L⁻¹ juice.

2.6. Statistical Analysis

The three-year data were analyzed by using year and treatment as fixed effects in ANOVA models. It was observed that the year effects for every measured attribute were non-significant and, for this reason, the three-year data were pooled and subjected to analysis. The data reported are the mean of replicates and expressed as mean ± standard deviation. Statistical analysis was performed via the use of SPSS v.27 packages (SPSS Inc., Chicago, IL, USA), with the use of one-way analysis of variance (one-way ANOVA). When there was a significant difference (p-value < 0.05), means were separated using Duncan’s test.

A principal component analysis was applied via the use of the SPSS v.27 packages (SPSS Inc., Chicago, IL, USA). Principal component analysis (PCA) is used for the determination of variables that provide a better explanation of observed differences.

3. Results

3.1. Circumference, Scion/Rootstock Ratio, and Tree Yield

Results indicate that the highest value of scion circumference was recorded for the cultivar ‘Nouvel Athos’ when grafted upon ‘Volkameriana’ rootstock (31 mm), while the lowest was recorded for the scion of the Italian cultivar ‘Femminello Commune’ when grafted upon ‘sour orange’ (17 mm). Furthermore, the highest values of rootstock circumference were recorded under the combination of ‘Nouvel Athos’/’Volkameriana’ rootstock (31 mm) and the lowest under the combination of ‘Mikrokarpo Messaras’/’sour orange’ rootstock (18 mm).

Trees of the lemon cultivars ‘Mikrokarpo Messaras’, ‘Femminello Commune’, and ‘Ziagara Bianca’ had smooth bud unions for all the studied rootstocks. The scion of the Georgian cultivar ‘Nouvel Athos’ tended to grow more when grafted upon ‘sour orange’ rootstock (1.37 ratio), while the Italian cultivar ‘Femminello Commune’ presented the lowest value of scion/rootstock ratio when grafted upon ‘sour orange’ (0.89 ratio) (

Table 1. Effect of rootstock on tree circumference, scion/rootstock ratio, and tree yield.

Variety	Rootstock	Scion Circumference	Rootstock Circumference	Scion/Rootstock Ratio	Tree Yield (Kg/Tree)
Mikrokarpo Messaras	Sour orange	20.67 ± 6.81 ab	18.33 ± 3.51 a	1.11 ± 0.22 ab	19.66 ± 3.06 a
	Yuma Ponderosa lemon	26.50 ± 3.97 abc	24.33 ± 4.04 abc	1.09 ± 0.03 ab	36.13 ± 1.97 c
	Volkameriana	27.17 ± 5.62 abc	26.00 ± 5.29 abc	1.04 ± 0.02 ab	25.89 ± 4.02 b
Nouvel Athos	Sour orange	28.67 ± 2.52 bc	21.00 ± 2.00 ab	1.37 ± 0.02 c	36.85 ± 3.71 c
	Yuma Ponderosa lemon	22.33 ± 0.58 bc	25.00 ± 1.00 abc	1.18 ± 0.07 bc	26.91 ± 4.16 b
	Volkameriana	31.67 ± 3.51 c	30.67 ± 1.53 c	1.03 ± 0.06 ab	49.67 ± 3.03 d
Femminello Commune	Sour orange	17.67 ± 0.58 a	20.67 ± 4.51 ab	0.89 ± 0.22 a	28.96 ± 1.35 b
	Yuma Ponderosa lemon	24.67 ± 7.51 abc	22.67 ± 4.51 abc	1.07 ± 0.12 ab	47.98 ± 1.95 d
	Volkameriana	27.00 ± 6.00 abc	24.00 ± 4.58 abc	1.12 ± 0.05 ab	60.38 ± 2.26 e
Ziagara Bianca	Sour orange	25.00 ± 9.17 abc	23.33 ± 6.66 abc	1.05 ± 0.10 ab	38.57 ± 1.45 c
	Yuma Ponderosa lemon	22.00 ± 5.57 abc	20.17 ± 6.60 ab	1.12 ± 0.17 ab	39.90 ± 1.77 c
	Volkameriana	28.00 ± 7.37 abc	27.83 ± 2.75 bc	1.00 ± 0.17 ab	53.06 ± 3.95 d

Means ± S.D. Different letters within the rows indicate statistically significant differences, according to Duncan’s multiple range test (p < 0.05).

). The rootstock choice did not affect the rootstock/scion ratio for the studied varieties of ‘Mikrokarpo Messaras’, ‘Femminello Commune’, and ‘Ziagara Bianca’.

The tree yields of the cultivars ‘Mikrokarpo Messaras’, ‘Nouvel Athos’, ‘Femminello Commune’, and ‘Ziagara Bianca’ were positively affected by 31.7%, 34.8%, 108.55, and 37.6%, respectively, when these cultivars were grafted upon the vigorous ‘Volkameriana’ rootstock, compared to ‘sour orange’. Also, when the cultivars ‘Mikrokarpo Messaras’ and ‘Femminello Commune’ were grafted upon the vigorous ‘Yuma Ponderosa lemon’ rootstock, an increase of 83.7% and 65.7% of fruit yield was recorded, compared to the mid vigor ‘sour orange’ (Table 1). The lowest tree yield was recorded when the ‘Mikrokarpo Messaras’ cultivar was grafted upon the mid-vigorous ‘sour orange’ rootstock (19 Kg/tree), while the highest value was recorded under the combination of ‘Femminello Commune’ and the vigorous ‘Volkameriana’ rootstock (60 Kg/tree).

3.2. Fruit Morphology and Fruit Mass

The lemon morphology and fruit mass were affected by the rootstock for each of the tested varieties (

Table 2. Effect of rootstock on fruit morphology and fruit mass.

Variety	Rootstock	Equatorial Diameter (mm)	Polar Diameter (mm)	Fruit Shape (E/P)	Fruit Mass (g)
Mikrokarpo Messaras	Sour orange	54.90 ± 0.26 a	65.23 ± 0.96 a	1.19 ± 0.02 bc	122.33 ± 4.51 a
	Yuma Ponderosa lemon	58.70 ± 0.40 b	68.13 ± 0.95 b	1.16 ± 0.01 ab	121.33 ± 3.06 a
	Volkameriana	59.00 ± 0.10 b	67.87 ± 0.61 b	1.15 ± 0.01 a	142.67 ± 3.79 b
Nouvel Athos	Sour orange	58.53 ± 0.60 b	74.80 ± 0.96 de	1.28 ± 0.01 gh	144.67 ± 4.16 b
	Yuma Ponderosa lemon	59.60 ± 0.78 b	76.90 ± 0.30 fg	1.29 ± 0.02 h	144.33 ± 4.16 b
	Volkameriana	59.63 ± 0.38 b	71.77 ± 0.96 c	1.20 ± 0.02 cd	144.33 ± 2.52 b
Femminello Commune	Sour orange	61.67 ± 0.67 c	75.87 ± 0.75 ef	1.23 ± 0.02 def	166.00 ± 2.65 d
	Yuma Ponderosa lemon	63.57 ± 0.57 d	80.20 ± 0.82 h	1.26 ± 0.02 fgh	180.67 ± 2.08 e
	Volkameriana	64.07 ± 0.81 d	77.30 ± 0.53 g	1.21 ± 0.02 cd	182.00 ± 2.65 e
Ziagara Bianca	Sour orange	61.20 ± 0.92 c	75.00 ± 0.70 de	1.23 ± 0.01 de	156.67 ± 2.52 c
	Yuma Ponderosa lemon	59.27 ± 0.81 b	74.20 ± 1.01 d	1.25 ± 0.02 efg	153.33 ± 1.53 c
	Volkameriana	63.20 ± 0.46 d	77.47 ± 0.60 g	1.23 ± 0.02 de	184.67 ± 2.52 e

Means ± S.D. Different letters within the rows indicate statistically significant differences, according to Duncan’s multiple range test (p < 0.05).

). Trees of the cultivars ‘Mikrokarpo Messaras’ and ‘Femminello Commune’, when grafted upon ‘Yuma Ponderosa lemon’ or ‘Volkameriana’, produced fruits with increased ED and PD, compared to ‘sour orange’. The use of ‘Volkameriana’ rootstock also increased the ED and PD of the fruits of the cultivar ‘Ziagara Bianca’, compared to ‘sour orange’ (Table 2). The highest value of ED was witnessed on lemon fruits of the cultivar ‘Femminello Commune’ grafted upon ‘Yuma Ponderosa lemon’ (63.5 mm), while the lowest value was recorded on fruits of the cultivar ‘Mikrokarpo Messaras’ grafted upon ‘sour orange’ (55 mm). Generally, the fruit of the Italian cultivars had higher values of ED when compared to the Greek and Georgian cultivars. Also, the PD was higher to the fruits of the cultivar ‘Femminello Commune’ when grafted upon the vigorous ‘Yuma Ponderosa lemon’ (80 mm), while the lowest value of PD was recorded for the fruit of the cultivar ‘Mikrokarpo Messaras’ grafted upon the mid-vigorous ‘sour orange’ rootstock (65.23 mm). It was witnessed that the cultivar ‘Mikrokarpo Messaras’ had the lowest ED and PD, while the Italian cultivar ‘Femminello Commune’ had the highest values (Table 2).

The rootstock choice affected the shape of the lemon fruit. Results indicate that for the local cultivar ‘Mikrokarpo Messaras’ and the Georgian cultivar ‘Nouvel Athos’, the ‘Volkameriana’ rootstock had the tendency to produce rounder fruits since the value of the E/P ratio was significantly decreased, compared to ‘sour orange’ rootstock. The highest value for fruit shape was recorded under the combination of ‘Nouvel Athos’ and the vigorous rootstock ‘Yuma Ponderosa’ (1.29 ratio), while the lowest was recorded under the combination of ‘Mikrokarpo Messaras’ and ‘Volkameriana’ rootstock (1.15 ratio).

Fruits of ‘Mikrokarpo Messaras’, ‘Femminello Commune’, and ‘Ziagara Bianca’ had increased fruit mass by 16.6%, 9.6%, and 17.9%, respectively, when grafted upon ‘Volkameriana’ rootstock, compared to ‘sour orange’. Also, the use of ‘Yuma Ponderosa lemon’ rootstock increased by 8.8% the fruit mass of the cultivar ‘Femminello Commune’, compared to ‘sour orange’. The three studied rootstocks did not affect the fruit mass of the cultivar ‘Nouvel Athos’. Among the studied cultivars, the fruits of the local cultivar ‘Mikrokarpo Messaras’ and the Georgian ‘Nouvel Athos’ had the lowest mean mass when compared to the Italian cultivars ‘Femminello Commune’ and ‘Ziagara Bianca’ for all the studied rootstocks (Table 2). The highest value of fruit mass was recorded under the combination of ‘Ziagara Bianca’ and the vigorous ‘Volkameriana’ rootstock (185 g), while the lowest mass value was recorded under the combination of ‘Mikrokarpo Messaras’ and ‘Yuma Ponderosa’ (121 g).

3.3. Fruit Quality Attributes

The quality attributes of RT, seed number, juice content, TSS, TA, TSS/TA, and ascorbic acid content are shown in

Table 3. Effect of rootstock on fruit quality attributes.

Variety	Rootstock	Rind Τhickness (mm)	Seed Number	Juice Content (%)	Total Soluble Solids (°Brix)	Total Acidity (%)	TSS/TA Ratio	Ascorbic Acid (mg/100 mL)
Mikrokarpo Messaras	Sour orange	4.54 ± 0.15 ab	9.67 ± 0.58 b	30.43 ± 0.83 b	7.74 ± 0.08 f	5.18 ± 0.14 f	1.50 ± 0.03 abc	33.17 ± 1.97 b
	Yuma Ponderosa lemon	4.83 ± 0.18 bc	14.00 ± 1.00 c	29.00 ± 0.78 a	6.4 ± 0.07 bc	4.54 ± 0.14 c	1.51 ± 0.06 bcde	33.04 ± 1.15 b
	Volkameriana	4.36 ± 0.10 a	10.00 ± 1.00 b	29.53 ± 1.03 ab	7.06 ± 0.12 d	4.54 ± 0.09 c	1.55 ± 0.01 cde	33.31 ± 1.82 b
Nouvel Athos	Sour orange	6.45 ± 0.25 d	8.67 ± 0.58 b	29.17 ± 0.65 ab	7.35 ± 0.16 e	4.77 ± 0.20 d	1.54 ± 0.09 cde	34.96 ± 0.38 bc
	Yuma Ponderosa lemon	6.68 ± 0.33 d	3.33 ± 0.58 a	28.30 ± 0.61 a	6.75 ± 0.06 b	4.20 ± 0.11 a	1.61 ± 0.04 e	36.60 ± 2.71 c
	Volkameriana	6.66 ± 0.31 d	9.00 ± 1.00 b	28.27 ± 0.40 a	6.83 ± 0.12 bc	4.41 ± 0.23 abc	1.55 ± 0.10 cde	35.61 ± 0.67 bc
Femminello Commune	Sour orange	5.26 ± 0.17 c	21.67 ± 1.53 e	33.10 ± 0.50 c	7.00 ± 0.02 cd	5.01 ± 0.10 ef	1.40 ± 0.03 a	22.89 ± 1.23 a
	Yuma Ponderosa lemon	5.27 ± 0.37 c	17.33 ± 0.58 d	32.50 ± 0.70 c	6.50 ± 0.10 a	4.47 ± 0.09 bc	1.45 ± 0.01 abc	24.43 ± 1.59 a
	Volkameriana	5.17 ± 0.44 c	16.00 ± 1.00 d	31.90 ± 0.70 c	6.79 ± 0.10 b	4.80 ± 0.10 de	1.1 ± 0.05 ab	24.20 ± 2.15 a
Ziagara Bianca	Sour orange	5.33 0.14 c	17.00 ± 1.00 d	31.98 ± 0.45 c	7.40 ± 0.10 e	4.98 ± 0.02 def	1.49 ± 0.01 abc	23.71 ± 2.50 a
	Yuma Ponderosa lemon	5.07 ± 0.12 c	16.67 ± 1.15 d	28.68 ± 0.96 a	6.82 ± 0.10 bc	4.28 ± 0.10 ab	1.60 ± 0.05 de	25.03 ± 1.38 a
	Volkameriana	5.18 ± 0.30 c	16.67 ± 1.15 d	33.12 ± 1.08 c	6.82 ± 0.11 bc	4.52 ± 0.10 c	1.51 ± 0.05 bcd	24.17 ± 0.97 a

Means ± S.D. Different letters within the rows indicate statistically significant differences, according to Duncan’s multiple range test (p < 0.05).

.

In the current study, the use of ‘Yuma Ponderosa lemon’ or ‘Volkameriana’ rootstock did not affect the RT of the fruits of all the studied cultivars, when compared to the ‘sour orange’ rootstock. In general, among the studied cultivars, the fruits of the local cultivar ‘Mikrokarpo Messaras’ had the lowest RT (mean value 4.6 mm) while the fruits from the Georgian cultivar ‘Nouvel Athos’ presented the highest values (mean value 6.6 mm) (Table 3). The highest value of RT was recorded under the combination of ‘Nouvel Athos’ and the vigorous ‘Yuma Ponderosa’ rootstock (6.7 mm), while the lowest mass value was recorded under the combination of ‘Mikrokarpo Messaras’ and ‘Volkameriana’ (4.3 mm).

Seed number was strongly affected in the studied cultivars by the used rootstock. The use of ‘sour orange’ rootstock positively influenced the number of seeds in the fruits of ‘Mikrokarpo Messaras’, ‘Nouvel Athos’, and ‘Femminello Commune’, with the latter variety demonstrating the highest value (22 seeds/fruit). The use of ‘Yuma Ponderosa lemon’ rootstock positively influenced the number of seeds in the fruits of ‘Mikrokarpo Messaras’ by 45%, but negatively influenced their number in the fruits of ‘Nouvel Athos’ and ‘Femminello Commune’ by 62% and 20%, respectively, compared to ‘sour orange’ rootstock. The use of ‘Volkameriana’ rootstock presented similar results to those of the use of ‘sour orange’ when ‘Mikrokarpo Messaras’ and ‘Nouvel Athos’ were grafted. The combination of ‘Yuma Ponderosa lemon’ and ‘Femminello Commune’ produced fruits with a decreased number of seeds, by 26%, compared to ‘sour orange’. The fruit seed number of the cultivar ‘Ziagara Bianca’ was not affected by the used rootstock. In general, the fruits from the Greek variety ‘Mikrokarpo Messaras’ and the Georgian variety ‘Nouvel Athos’ had fewer mean values of seeds (11 and 7, respectively) than the Italian varieties ‘Femminello Commune’ (18) and ‘Ziagara Bianca’ (17), independently of the used rootstock (Table 3).

Among the used rootstock–scion combinations, only the use of ‘Yuma Ponderosa lemon’ significantly affected the juice content of the fruits of the cultivars ‘Mikrokarpo Messaras’ and ‘Ziagara Bianca’, by decreasing this attribute by 5% and 10%, respectively, when compared to ‘sour orange’ (Table 3). For all the studied cultivars, when grafted upon ‘Volkameriana’ rootstock, their fruits exhibited similar values of juiciness to those of ‘sour orange’. In general, the lemon fruits of the Greek lemon varieties ‘Mikrokarpo Messaras’ and the Georgian ‘Nouvel Athos’ had lower juice content, when grafted upon ‘sour orange’ or ‘Volkameriana, compared to the Italian cultivars ‘Femminello Commune’ and ‘Ziagara Bianca’, grafted upon the same rootstocks. The highest value of fruit juiciness was recorded under the combination of ‘Ziagara Bianca’ and the vigorous ‘Volkameriana’ rootstock (33%), while the lowest value was recorded under the combination of ‘Nouvel Athos’ and ‘Volkameriana’ (28%) (Table 3).

In the current study, the rootstock choice significantly affected the TSS content of the fruits produced by the grafted cultivar (Table 3). When the ‘Yuma Ponderosa lemon’ was used as a rootstock, the TSS content of the fruits of the cultivars ‘Mikrokarpo Messaras’, ‘Nouvel Athos’, ‘Femminello Commune’, and ‘Ziagara Bianca’, exhibited a significant decrease of 11.6%, 8.3%, 7.1%, and 7.9%, respectively, compared to ‘sour orange’. Furthermore, when the ‘Volkameriana’ rootstock was used, a similar decrease of 8.7%, 7.2%, 3.1%, and 7.9%, respectively, was witnessed compared to the ‘sour orange’, of the TSS content from the fruits of ‘Mikrokarpo Messaras’, ‘Nouvel Athos’, ‘Femminello Commune’, and ‘Ziagara Bianca’. The highest value of TSS was recorded under the combination of ‘Mikrokarpo Messaras’ and the mid-vigorous ‘sour orange’ rootstock (7.74 °Brix), while the lowest value was recorded under the combination of ‘Femminello Commune’ and ‘Yuma Ponderosa lemon’ (6.50 °Brix) (Table 3).

The rootstock choice significantly affected the TA content of the lemon fruits of the grafted cultivars (Table 3). The use of ‘Yuma Ponderosa lemon’ rootstock exhibited a greater decrease in this quality attribute when compared to the ‘Volkameriana’ rootstock, for all grafted lemon cultivars. When the ‘Yuma Ponderosa lemon’ was used as a rootstock, the TA of the fruits of the cultivars ‘Mikrokarpo Messaras’, ‘Nouvel Athos’, ‘Femminello Commune’, and ‘Ziagara Bianca’ exhibited a significant decrease of 12.2%, 12.1%, 10.8%, and 14.2%, respectively, compared to ‘sour orange’. Furthermore, when the ‘Volkameriana’ rootstock was used, a similar decrease of 12.2%, 7.7%, 4.3%, and 9.4% respectively, was witnessed compared to ‘sour orange’, of the TA % of the fruits of ‘Mikrokarpo Messaras’, ‘Nouvel Athos’, ‘Femminello Commune’, and ‘Ziagara Bianca’ cultivars. The highest value of ΤA was recorded under the combination of ‘Mikrokarpo Messaras’ and the mid-vigorous ‘sour orange’ rootstock (5.18%), while the lowest value was recorded under the combination of ‘Nouvel Athos’ and ‘Yuma Ponderosa lemon’ (4.2%) (Table 3).

Trees of all tested varieties, on all studied rootstocks, produced fruits with a similar TSS/TA ratio, except when the cultivar ‘Ziagara Bianca’ was grafted upon ‘Yuma Ponderosa lemon’, whose combination of the fruits increased TSS/TA ratio by 7.4% (Table 3). Generally, the TSS/TA ratio was not affected by the rootstock choice for the specific grafted cultivars.

The ascorbic acid content of the fruits produced, from all studied varieties, was affected by the rootstock choice. In general, the fruit of the Greek local variety ‘Mikrokarpo Messaras’ and the Georgian ‘Nouvel Athos’, grafted to all the studied rootstocks, had significantly higher mean ascorbic acid content (around 36 mg 100 mL⁻¹ and 37.5 mg 100 mL⁻¹, respectively) when compared to the Italian cultivars ‘Femminello Commune’ and ‘Ziagara Bianca’ (around 25.5 mg 100 mL⁻¹ and 26 mg 100 mL⁻¹, respectively) (Table 3). When the ‘Yuma Ponderosa lemon’ was used as a rootstock, there was a 12.94%, 8.4%, 15.83%, and 16.5% increase in the ascorbic acid content of the fruit of the ‘Mikrokarpo Messaras’, ‘Nouvel Athos’, ‘Femminello Commune’, and ‘Ziagara Bianca’ cultivars, respectively, compared to ‘sour orange’. While the most positive impact was witnessed when the ‘Volkameriana’ rootstock was used, where there was an increase of 14.9%, 12.74%, 18.88%, and 19.75%, in the ascorbic acid content of the fruits of the ‘Mikrokarpo Messaras’, ‘Nouvel Athos’, ‘Femminello Commune’, and ‘Ziagara Bianca’ cultivars, respectively, compared to ‘sour orange’. The highest value of ascorbic acid was recorded under the combination of ‘Nouvel Athos’ and the vigorous ‘Volkameriana’ rootstock (39.5 mg 100 mL⁻¹), while the lowest value was recorded under the combination of ‘Femminello Commune’ and ‘sour orange’ (22.8 mg 100 mL⁻¹) (Table 3).

3.4. Antioxidant Activity and Total Phenolic Content

The total phenolics and antioxidant activity of the four lemon cultivars grafted upon three rootstocks under study are presented in

Table 4. Effect of rootstock on fruit total phenolics and antioxidant activity (FRAP values).

Variety	Rootstock	Total Phenolics (mg GAE/100 mL)	Total Antioxidant Activity (FRAP (mmol Trolox/L))
Mikrokarpo Messaras	Sour orange	406.67 ± 3.83 d	1.41 ± 0.09 eh
	Yuma Ponderosa lemon	404.63 ± 8.70 d	1.32 ± 0.07 e
	Volkameriana	400.61 ± 6.93 d	1.44 ± 0.04 h
Nouvel Athos	Sour orange	385.00 ± 5.98 c	1.07 ± 0.09 d
	Yuma Ponderosa lemon	380.99 ± 8.43 bc	1.03 ± 0.06 d
	Volkameriana	377.66 ± 9.42 bc	0.97 ± 0.07 d
Femminello Commune	Sour orange	374.81 ± 3.18 bc	1.03 ± 0.06 d
	Yuma Ponderosa lemon	367.39 ± 12.21 b	0.98 ± 0.11 d
	Volkameriana	372.40 ± 12.31 b	0.85 ± 0.03 c
Ziagara Bianca	Sour orange	337.28 ± 3.09 a	0.47 ± 0.05 b
	Yuma Ponderosa lemon	327.43 ± 3.87 a	0.37 ± 0.07 ab
	Volkameriana	334.09 ± 4.44 a	0.34 ± 0.04 a

Means ± S.D. Different letters within the rows indicate statistically significant differences, according to Duncan’s multiple range test (p < 0.05).

.

Results indicate that the rootstock choice did not influence the amount of phenol contents that were produced within the fruit of any of the grafted varieties, since no statistical differences were found among the fruits of the same cultivar (Table 4). In general, the Greek local variety ‘Mikrokarpo Messaras’ and the Italian cultivar ‘Ziagara Bianca’ had the highest (404 mg GAE 100 mL⁻¹) and the lowest (333 mg GAE 100 mL⁻¹), respectively, mean value of phenolics within the fruit, independently of the rootstock used. Also, the fruits of the cultivars ‘Nouvel Athos’ and ‘Femminello Commune’ presented similar mean values of phenolics (381 mg GAE 100 mL⁻¹ and 371 mg GAE 100 mL⁻¹, respectively) when grafted to any of the tested rootstocks (Table 4). The highest value of phenolics was recorded under the combination of ‘Mikrokarpo Messaras’ and the mid-vigorous ‘sour orange’ rootstock (407 mg GAE 100 mL⁻¹), while the lowest value was recorded under the combination of ‘Ziagara Bianca’ and the vigorous ‘Yuma Ponderosa’ rootstock (327 mg GAE 100 mL⁻¹) (Table 4).

Results indicate that the rootstock choice did not influence the antioxidant capacity of the lemons of the studied varieties, since no statistical differences were found (Table 4). It was witnessed that the lemon fruit of the Greek local variety ‘Mikrokarpo Messaras’ exhibited the highest mean antioxidant activity (1.39 mm Trolox L⁻¹) when compared to the Italian cultivar ‘Ziagara Bianca’, with the latter variety having the lowest values (0.39 mm Trolox L⁻¹), independently of the rootstock used. Furthermore, the fruits of the cultivars ‘Nouvel Athos’ and ‘Femminello Commune’ presented similar mean antioxidant capacities (1.0 and 0.95 mm Trolox L⁻¹, respectively) when grafted to any of the tested rootstocks (Table 4). The highest value of antioxidant activity was recorded under the combination of ‘Mikrokarpo Messaras’ and the vigorous ‘Volkameriana’ rootstock (1.44 mm Trolox L⁻¹), while the lowest value was recorded under the combination of ‘Ziagara Bianca’ and the vigorous ‘Volkameriana’ rootstock (0.34 mm Trolox L⁻¹) (Table 4).

3.5. Principal Component Analysis (PCA)

In the current work, a PCA analysis was conducted, including all the studied cultivars and rootstock, using 17 variables previously presented (Table 1, Table 2, Table 3 and Table 4). The variance of data that was explained by the PCA model regarding cultivars was 84.3% and rootstocks were 100%; where PC1 explained 50.5% and 59%, and PC2 33.8% and 41% of the total variance, respectively. A clear separation between the cultivars ‘Mikrokarpo Messaras’ and ‘Nouvel Athos’ (positive values), and cultivars ‘Ziagara Bianca’ and ‘Femminello Commune’ (negative values) based on PC1 was observed (Figure 1). Moreover, based on PC2 ‘Mikrokarpo Messaras’ separated from ‘Nouvel Athos’, in parallel, ‘Ziagara Bianca’ separated from ‘Femminello Commune’. Furthermore, a clear discrimination among rootstocks was detected, especially, based on PC1, ‘sour orange’ separated from the other two rootstocks, and based on PC2, ‘Volkameriana’ separated from ‘Yuma Ponderosa lemon’ (Figure 1).

4. Discussion

The proper selection of rootstocks is crucial for the future productivity and success of the new lemon grove, as stated by various scientific groups [3,4,5,10,17]. Therefore, it is essential to obtain data that will provide new clues about the interplay that exists among specific commercial varieties and rootstocks under certain microclimates. In our study, conducting all experiments in the same grove and location with common soil, climate, and cultivation management allowed us to determine the potential impact of rootstock selection on scion agronomic and qualitative characteristics.

Measurement of the scion and rootstock circumference facilitates the estimation of the scion/rootstock diameter ratio, which serves as a potent indicator of compatibility, and values close to one (1) indicate very good affinity [18]. Our study found that the majority of the studied cultivars exhibited values close to one, for all tested rootstocks, indicating good compatibility. Similar results were reported in previous studies for the lemon cultivars ‘Lapithou’ and ‘Interdonato’ from other groups [4,19]. In detail, in the work of Georgiou et al. [4], the scion/rootstock ratio for the cultivar ‘Lapithou’ was 1.09, 0.92, and 1.07 when ‘sour orange, ‘Yuma Ponderosa lemon’ and ‘Volkameriana’ were used as rootstock, respectively. Regarding fruit tree yield, the use of the vigorous ‘Volkameriana’ rootstock significantly increased the overall tree yield of all tested cultivars compared to ‘sour orange’. Especially the combination of ‘Femminello Commune’/‘Volkameriana’ exhibited a tree yield of 60 Kg/tree, compared to the 29 Kg/tree witnessed when the same cultivar was grafted upon the mid-vigorous ‘sour orange’ rootstock. Our data align with current literature indicating that the vigorous ‘Volkameriana’ rootstock favors citrus tree development and total fruit yield [4]. Our result supports the statement made by Tietel et al. [20] that ‘Volkameriana’ rootstock effect on citrus tree yield is scion-dependent and its use favors the establishment of a root structure of vigorous trees that supports the production of more fruit quantities. The latter proposal is also further supported by the use of the vigorous ‘Volkameriana’ rootstock which favored the production of fruits with increased fruit mass. It is notable the fact that the Italian cultivars ‘Femminello Commune’ and ‘Ziagra Bianca’ produced fruits of almost 180 g, compared to the 160 g obtained when the mid-vigorous ‘sour orange’ rootstock was used.

Fruit size is a critical quality trait in citrus fruits, determining their acceptance in fresh fruit markets or suitability for industrial processing. Small-sized fruits are often destined for processing facilities or used as fresh fruit. Large and medium fruits are the ones that receive the highest prices in the market [5]. In the work of Aguilar-Hernandez et al. [3], it was proposed that a lemon fruit is characterized as small when the ED is around 55 mm, the PD is around 70 mm, and the fruit mass is near 100 g, while a lemon fruit can be characterized as big when the ED is near 67 mm, the PD near 85 mm and the fruit mass is near 185 g. In our study, it was found that the fruit of the Greek cultivar ‘Mikrokarpo Messaras’ could be characterized as small, only when the ‘sour orange’ rootstock was used. Under the effect of the vigorous ‘Yuma Ponderosa lemon’ and ‘Volkameriana’ rootstocks the fruit of the ‘Mikrokarpo Messaras’ became mid-sized and were commercially acceptable. However, using ‘Volkameriana’ rootstock resulted in significantly more rounded fruits for ‘Mikrokarpo Messaras’ and ‘Nouvel Athos’ compared to ‘sour orange’, consistent with previous research [4]. The use of Volkameriana rootstock also increased fruit weight for the Greek cultivars ‘Mikrokarpo Messaras,’ ‘Femminello Commune,’ and ‘Ziagara Bianca,’ corroborating findings from other studies [4,10]. This positive effect upon the size, shape, and fruit mass of the use of the vigorous rootstocks (‘Yuma Ponderosa lemon’ and ‘Volkameriana’) could be attributed to the fact that vigorous rootstocks develop an extensive root system that more efficiently utilizes the absorbed water [17].

Juice content is a crucial quality attribute for lemons since juicer fruits are more accepted by the fresh market and processing facilities. For this reason, certain limits have been established so as to secure the delivery of quality fruit to the production and market chain [17]. Only fruits that exceed the limit of 20% juice content are accepted by the market [21]. It is known that lemon juice content can be affected by the used rootstock [17]. In our work, all studied varieties under each rootstock combination exceeded the accepted limit for market use (20%), indicating ample juice availability. While the use of ‘Yuma Ponderosa lemon’ rootstock reduced juice content for ‘Mikrokarpo Messaras’ and ‘Ziagara Bianca’, ‘Volkameriana’ rootstock had no significant influence. Previous research also suggests rootstock choice affects juice content [5,10]. In the work of Dubey and Sharma [5], the use of rough lemon and RLC-4 rootstocks favored the juice content of the produced lemon fruits, reaching values of nearly 40%. Furthermore, in the work of Al-Jaleel et al. [10], the use of ‘Volkameriana’ as a rootstock for ‘Eureka’ lemons produced fruits with fruit juice content near 39%, while for the same variety, the use of ‘Cleopatra mandarin’ or ‘Amblycarpa’ favored the fruit juice content, reaching values of near 42%.

Total soluble solids (TSS) and total acidity (TA) play essential roles in determining the overall palatability of citrus fruit [22]. It is stated that the TSS of lemon juice should not be ignored since it contributes significantly to the quality of the fruit [10]. Our study found that the use of ‘Yuma Ponderosa lemon’ or ‘Volkameriana’ rootstock significantly decreased both the TSS and TA content of lemon fruits from all studied cultivars compared to ‘sour orange’. This result is in accordance with the work of Georgiou et al. [4], who demonstrated that when ‘Yuma Ponderosa lemon’ or ‘Volkameriana’ was used as a rootstock for the lemon cultivar ‘Lapithou’ the TSS and TA content were near 10 °Brix and 1.37%, respectively. Also, in the work of Al-Jaleel et al. [10] lemons of the ‘Eureka’ variety grafted upon the vigorous ‘Volkameriana’ rootstock exhibited lower TSS content (7.6%) and TA % (5.9%), compared with the same variety grafted upon ‘sour orange’ (8.65% TSS and 5.93% TA). Furthermore, the use of vigorous rootstocks, like ‘citrus taiwanica’, ‘rough lemon’ and ‘Volkameriana’ for the production of lemons and limes, results in fruits with low TSS content compared to fruits produced by ‘Cleopatra mandarin’ and ‘sour orange’ [10]. The selection of vigorous rootstocks like ‘Yuma Ponderosa lemon’ or ‘Volkameriana’ may lead to fruits with low TSS and TA content, a fact that has a negative impact on fruit quality [10,20]. Our results also support the proposal of Al-Jaleel et al. [10] that the juice from citrus fruit grown on vigorous lemon rootstocks tends to have a relatively low TA content.

Citrus fruits, especially lemons, are known for their rich ascorbic acid (vitamin C) content, which plays a vital role in various human metabolic processes and in the support of the immune system [23]. In our study, the mean value of the ascorbic acid from all studied cultivars was around 31 mg 100 mL⁻¹, a value that is within the range of previously reported lemon juice ascorbic acid concentrations proposed by other scientific groups (20–51 mg 100 mL⁻¹) [24]. It is estimated that by consuming three lemons, an adult human can cover the daily needs (RDA) for vitamin C [25]. Using ‘Volkameriana’ or ‘Yuma Ponderosa lemon’ rootstock positively influenced the ascorbic acid content in the fruits of all studied cultivars compared to ‘sour orange’, a result which is in line with previous research [26,27,28]. In the work of Emmanouilidou and Kyriakou [26], the use of the vigorous rootstock ‘Volkameriana’ induced the production of ascorbic acid to the fruit of ‘Lane Late’ and ‘Delta’ oranges, when these varieties were grafted upon the latter rootstock. Also, in the work of Morales et al. [27], mandarin fruit of the cultivar ‘Clemenules’, when grafted upon the vigorous rootstock ‘Volkameriana’ exhibited increased levels of ascorbic acid in the juice of the produced fruit, compared to less vigorous rootstocks like Forner—Alcaide 5 and Forner—Alcaide 13. Based upon these data, it can be proposed that vigorous rootstocks could favor ascorbic acid content to the grafted scion variety.

It is well-documented that the consumption of citrus fruit has a beneficial impact to human health [29]. Several studies support the anti-inflammatory, anti-bacterial, anti-cancer, and hepatoprotective properties of citrus [30]. These properties are attributed to phenolic compounds (flavones and flavanones), which are substances with high antioxidant potential [31]. Furthermore, the phenolic fraction contributes to the overall taste and organoleptic sensory quality of the fruit due to its direct participation in the development of the rind and flesh color, astringency, and/or palatability [3]. In this research work, we found the highest concentration of phenolics (404 mg GAE/100 mL) in the Greek lemon cultivar ‘Mikrokarpo Messaras’ and the lowest (333 mg GAE/100 mL) in the Italian cultivar ‘Ziagara Bianca,’ independently of the cultivar/rootstock combination. Our data are within the range of reported values (226–396 mg GAE mL⁻¹) [3,17] and are also in accordance with recent groups that reported that rootstock choice does not influence the phenol production of the lemon scion [3,10]. In the work of Aguilar-Hernandez et al. [3], the total phenolic content of lemons from the cultivar ‘Verna’, obtained in different rootstocks, ‘Citrus macrophylla’, or ‘sour orange’, did not vary among the cultivar/rootstock combination (‘Verna’/‘C. macrophylla’: 281 mg GAE 100 mL⁻¹—‘Verna’/’sour orange’: 331 mg GAE 100 mL⁻¹, with no statistically significant differences between them). Our data support the assumption that the total phenolic content varies from one cultivar to another, a characteristic that is linked to the genetic profile of the cultivar [32]. Additionally, the fact that the Greek cultivar ‘Mikrokarpo Messaras’ has the highest amount of total phenolics could be linked to its status as the most drought-tolerant among the studied cultivars.

Lemons are also known for their antioxidant activity, linked to their phenolic content [33]. Our results found that the use of ‘Yuma Ponderosa lemon’ rootstock did not influence the fruit’s total antioxidant capacity for all studied cultivars, compared to ‘sour orange’ rootstock. While the fruits from the Italian cultivars ‘Femminello Commune’ and ‘Ziagara Bianca’ exhibited a lower amount of total antioxidant activity when grafted upon the ‘Volkameriana’ rootstock. In general, the highest antioxidant capacity, evaluated by the FRAP method, was witnessed in the fruit of ‘Mikrokarpo Messaras’, while the lowest was observed in the fruits of the Italian variety ‘Ziagara Bianca’. Our data are in line with the literature, which indicates the FRAP values of most lemon varieties are near 1 [3,9,17] and that the ‘Volkameriana’ rootstock does not favor citrus fruit antioxidant capacity [34,35]. In our study, the differences between the studied cultivars might be associated with the genetic profile of the cultivar [36]. In general, antioxidant capacity is a multivariant attribute that is, basically, associated with the amount and presence of antioxidants with similar structure, isomerism, stereochemistry, and the high or low concentration of phenols (flavones or flavonones) [17].

5. Conclusions

In conclusion, our study highlights the notable benefits of using ‘Volkameriana’ rootstocks for the studied lemon cultivars, leading to increased tree yield, fruit mass, and ascorbic acid content. It also promotes the production of more rounded fruits while reducing total soluble and total acid content without affecting other fruit attributes. ‘Yuma Ponderosa’ rootstock shows positive effects on tree yield and ascorbic acid content for certain cultivars, but it also leads to some changes in fruit shape and juice content. However, the maturation index, rind thickness, total phenolics, and antioxidant activity remain unaffected. These results suggest that the vigorous ‘Volkameriana’ and ‘Yuma Ponderosa lemon’ could be promising alternatives to ‘sour orange’ in Greek lemon groves. Our study contributes valuable scientific insights into the utilization of ‘Yuma Ponderosa lemon’ as a viable rootstock for lemons, which is relatively limited in the existing literature. These findings are valuable for lemon growers and the scientific community, guiding sustainable and optimized lemon cultivation practices. Further research and practical applications are needed to fully understand and utilize the potential benefits of these rootstocks under various environmental and agronomic conditions.