Salinity stress effects on growth and performance of drip ...

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Salinity stress effects on growth and performance of drip-irrigated sweetpotato varieties under the Mediterranean conditionsKivanc Hayri Doganay

Dicle UniversityAhmet Kurunc ( [email protected] )

Akdeniz UniversityCuneyt Dincer

Akdeniz University

Research Article

Keywords:

Posted Date: February 28th, 2022

DOI: https://doi.org/10.21203/rs.3.rs-1365542/v1

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AbstractThere is numerous scienti�c research on yield response of different sweet potato varieties under salinity stress, but no studies on theKoganesengan and Beniazuma varieties have been found in the literature. The aim of this study was to investigate the effects of irrigation salinitylevels on growth, yield and quality parameters of these two sweet potato varieties under drip irrigation. Salinity levels had a substantial impact onsome growth and yield parameters of ‘Beniazuma’, but not on those of ‘Koganesengan’. Irrigation salinity levels only in�uenced the crude �bercontent and antioxidant activity of ‘Koganesengan’ and ash, starch, ß-carotene, and ascorbic acid contents of ‘Beniazuma’. Some growth and yieldquality parameters showed signi�cant differences between varieties under salinity level(s), and all yield parameters (except dry vine yield) onlyunder control treatment. Under the same salt stress levels, the values of the examined parameters were greater in ‘Beniazuma’ than in‘Koganesengan’. The salinity threshold and slope values, on the other hand, suggest that ‘Beniazuma’ is more vulnerable to salt stress than‘Koganesengan’. As a result, sweet potato growers in the Mediterranean region should consider both the salt response and the productivity of thesesweet potato varieties under drip irrigation with saline water.

IntroductionAmong the 50 genera and more than 1000 species of the Convolvulaceae family, sweet potato (Ipomoea batatas L.) is one of the remarkableagricultural plants. Being a perennial crop, it can be usually grown as annual in the tropical, sub-tropical, and frost-free temperate climate zones ofthe world1. After rice, wheat, maize, and cassava the plant ranks �fth in terms of annual fresh-weight production in developing countries2. Sweetpotatoes are grown for their tubers and leaves since all parts of the plant can be completely used3. Its stems and leaves are fed to livestock ineither dried or fresh form4. Plant leaves as a vegetable are high in proteins, vitamins, and various minerals whereas tubers are rich in vitamins andminerals. The plant is a high value-added food especially for youngsters and pregnant women, who are more likely to be de�cient in vitamin A1.Furthermore, it is therapeutically important because of its excellent bioactivities i.e. anticancer5,6, antihyperglycemic7, antimutagenic8,9, antioxidantactivities10,11, hepatoprotective12 and radical scavenging13. The commercial cultivation of sweet potatoes has attracted the interest of manycountries outside of the traditional production zones, particularly in warm coastal regions, due to their wide adaptability to various climate andfarming techniques14,15.

Salinity is one of the most important stress factors that limit the growth, development, and yield of the plant16,17. It is estimated that the salinityproblem will affect more than half of the agricultural lands until 205018. According to published �ndings, environmental and genetic factors, aswell as cultural management practices, can considerably in�uence a crop's sensitivity to stress conditions. Plants cultivated in salty soils react tosalinity in different manners due to their genotypic variations19. These differences in salt stress responses apply to different plant species anddifferent varieties of the same plant species20,21.

Although there are some scienti�c studies on plant growth and yield for different sweet potato varieties under salinity stress, no studies on‘Koganesengan’ and ‘Beniazuma’ varieties have been found in the literature. Therefore, this study was conducted Although several scienti�c studieson plant development and yield for some sweet potato varieties under salinity stress have been identi�ed in the literature, no studies on the'Koganesengan' and 'Beniazuma' varieties have been found. As a consequence, the purpose of this study was to investigate the effects of differentirrigation salinity levels on the growth, yield, and quality parameters of these two sweet potato varieties that were recently introduced to Turkey'sMediterranean region.

ResultsEffects on soil and growth parameters. Among the investigated parameters, vine length (P ≤ 0.01), tuber diameter, and the number of leaves (P ≤ 0.05) averaged over irrigation water salinity levels had signi�cant differences between varieties. Similarly, only ECe, pHe, and the number of shootsaveraged over varieties were signi�cantly different (P ≤ 0.01) among salinity levels (Table 2).

When each variety is evaluated separately, it can be concluded that irrigation salinity levels affected the ECe and pHe values of the soil on the sub-plots of both varieties, but not the growth parameters of either variety except the number of shoots for ‘Beniazuma’. Increased irrigation watersalinity levels caused increases in soil ECe, but decreases in soil pHe values, as expected. On both sweet potato parcels, the highest soil salinityvalues (9.13 and 9.54 dS/m) were measured under very high salinity treatments, while the lowest values (1.30 and 1.23 dS/m) were obtained undercontrol treatments. However, soil salinity under low irrigation water salinity treatment (2.82 dS/m) of ‘Koganesengan’ was not statistically differentfrom that of the control (Table 2). Compared to the control treatment, soil salinities increased by 3.8, 5.6, and 7.0 times under medium, high, andvery high salinity levels of ‘Koganesengan’ and by 2.2, 3.9, 5.7, and 7.8 times under low, medium, high, and very high salinity levels of ‘Beniazuma’,respectively. The ‘Beniazuma’ variety produced the highest number of shoots (14.33 per plant) under control salinity treatment.

Statistical analysis revealed that, in addition to the number of shoots and tubers under the control treatment, vine lengths under low, medium, andhigh salinity treatments of ‘Beniazuma’ were signi�cantly higher than those of ‘Koganesengan’ variety. In contrast, the average tuber diameter

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under high salinity and the number of leaves under low and medium salinity treatments of ‘Koganesengan’ were higher than those of the‘Beniazuma’ variety (Table 2).

Effects on yield parameters. None of the yield parameters including the fresh vine, dry vine, tuber, and total yields averaged over irrigation watersalinity levels showed signi�cant differences between varieties. Fresh vine and total yields averaged over varieties, on the other hand, weresigni�cantly different (P ≤ 0.05) among salinity levels (Table 3).

When each variety is evaluated separately, it can be concluded that irrigation salinity level has a signi�cant effect on fresh vine, dry vine, and totalyields of the ‘Beniazuma’ variety, but not on those of the ‘Koganesengan’. The highest fresh vine (27.88 t/ha), dry vine (4.09 t/ha), and total yields(50.79 t/ha) for ‘Beniazuma’ were achieved under the control treatment whilst the lowest values were observed under other salinity level treatmentswith no statistical signi�cance (Table 3). Compared to the control treatment, fresh vine, dry vine, and total yields of ‘Beniazuma’ were reduced by55.2, 48.4, and 44.3% under low; 53.1, 44.3, and 48.1% under medium; 52.5, 46.2, and 47.3% under high; and 56.7, 48.4, and 54.1% under very highirrigation water salinity level treatments, respectively.

According to statistical analysis, the fresh vine, dry vine, and total yields of ‘Beniazuma’ were signi�cantly higher than those of the ‘Koganesengan’variety under the control treatment. Under low, medium, high, and very high irrigation water salinity treatments, however, the varieties showed nosigni�cant differences for the same yield parameters (Table 3).

Effects on quality parameters. Antioxidant activity, crude �ber, starch, and ascorbic acid contents averaged over irrigation water salinity levels hadsigni�cant differences (P ≤ 0.01) between varieties, however dry matter, ash, phenolic matter, ß-carotene, protein, saccharose, glucose, and fructosecontents did not. Only the crude �ber and starch content averaged over varieties were signi�cantly different (P ≤ 0.01) among salinity leveltreatments (Table 4).

When each variety is examined separately, it can be concluded that irrigation salinity has no signi�cant effect on the dry matter, phenolic matter,protein, saccharose, glucose, and fructose contents of both varieties, as well as ash, starch, ß-carotene, and ascorbic acid contents of‘Koganesengan’ and crude �ber content, and antioxidant activity of ‘Beniazuma’. However, irrigation salinity level had a substantial impact on crude�ber content and antioxidant activity values of the ‘Koganesengan’ variety, as well as ash, starch, ß-carotene, and ascorbic acid contents for the‘Beniazuma’. The control treatment of the ‘Koganesengan’ variety yielded the highest crude �ber content and antioxidant activity. Compared tocontrol treatment, crude �ber content and antioxidant activity values of this variety were decreased 61.0, 22.3, 33.9, and 52.4%; and 39.7, 37.5, 42.4,and 30.2% under low, medium, high, and very high salinity level treatments, respectively. For the ‘Beniazuma’ variety, the highest value was obtainedfor ash content under low, medium and high salinity levels; for starch content under all salinity levels except control treatment; for ß-carotene undervery high salinity level; and ascorbic acid under control, low, medium and high salinity levels of (Table 4). Compared to control treatment, 41.2 and30.1% increases for ash content under medium and high salinity, 13.2, 13.3, 10.8 and 9.7% increases for starch content under low, medium, highand very high salinity, 75.5% increase for ß-carotene content under very high, and 35.5% decrease for ascorbic acid content under very high salinitytreatments were calculated.

Signi�cant differences for ash content under medium; crude �ber content under control and very high; starch content under low, medium, and high;antioxidant activity and ascorbic acid contents under medium and high; and glucose and fructose contents under control salinity treatments werealso found between varieties. All of the parameters (except crude �ber content under control treatment) of ‘Beniazuma’ were higher than those of‘Koganesengan’ under these treatments (Table 4).

Salt Tolerance Models. The threshold salinity and slope after the threshold values for vine, tuber, and total yields of the two sweet potato varietieswere attempted to be determined by generating salt tolerance models. It is important to note that, it was not possible to obtain threshold salinityvalues of both sweet potato varieties for these yield parameters if all salinity levels were considered since the slope lines of these parameters cutthe Y-axis below 100%. Therefore, only the yield values under control, low, medium, and high salinity treatments for ‘Koganesengan’; and the samevalues under control, high, and very high salinity treatments for ‘Beniazuma’ variety were taken into account to obtain yield response factors. Underthese conditions, the threshold salinity values of 2.83, 1.65, and 2.39 dS/m; and slope values of 8.15, 5.66, and 7.00% per dS/m were calculated forfresh vine, tuber, and total yields of ‘Koganesengan’. Similarly, for fresh vine, tuber, and total yields of ‘Beniazuma’, the threshold salinity and slopevalues were obtained as 0.86, 1.04, and 0.93 dS/m and 7.21, 6.30, and 6.80% per dS/m, respectively (Fig. 1).

DiscussionIn this study, different salt sources were mixed for generating saline waters to avoid a dominant in�uence of a particular ion and/or SAR on theresults, thus only the effects of overall salinity were investigated22–24. Soil EC and pH readings in the sub-plots of both varieties exhibited similarsubstantial differences among salinity levels, as expected. Under control, low, medium, high, and very high irrigation water salinity treatments, theECe/ECw ratios were 1.86, 1.88, 1.65, 1.62, and 1.52 for ‘Koganesengan’; and 1.76, 1.77, 1.60, 1.54, and 1.59 for ‘Beniazuma’ respectively. However,under the conventional irrigation method with a 25% leaching fraction, the ECe/ECw ratios were calculated as 1.17, 1.25, 1.69, and 2.34 for the

irrigation water salinities of 0.54, 1.8, 2.5, and 5.0 dS/m, respectively22. Under drip irrigation, salts can be removed from the active root zone, but

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not from the soils away from the root zone. The more stable ratios in this study may be attributed to the drip irrigation method, since the salt tendsto accumulate away from the active root zone horizontally, vertically, and also at the wetting front close to the soil surface25–27.

Some growth and yield parameters of the ‘Beniazuma’ variety were signi�cantly in�uenced by salinity level treatments, whilst increased salinity hasnot a signi�cant effect on the growth and yield parameters of ‘Koganesengan’. the growth and yield parameters for ‘Koganesengan’ were higherunder most of the salinity treatments than those under the control treatment, however, there was no signi�cant difference. According to Afaf et al.28

saline water at 10 and 30% seawater levels encouraged plant height, the number of leaves and branches, and dry shoot weight of sweet potatoesbut, all of these parameters were reduced at 50% seawater salinity level. Similarly, Rodríguez-Delfín et al.29 found a signi�cant increase in dry leafweight and leaf area of ‘Huambachero’ sweet potato variety under 3.0 dS/m and in dry tuber weight of ‘Untacip’ variety under 3.5 dS/m salinity.Compared to control treatment, even under low salinity treatment, a sharp decrease was observed for the number of shoots, fresh vine yield, dryvine yield, and tuber yield of ‘Beniazuma’ variety, indicating that this variety is more sensitive to salinity than ‘Koganesengan’. A similar resultreported by Dasgupta et al.30 that increased salt concentrations in sweet potato varieties caused a signi�cant decrease in the number of leaves,shoots, and roots, as well as shoot and root lengths of sweet potatoes. However, Afaf et al.28 stated that yield parameters of the sweet potatovarieties signi�cantly increased under saline water with 10% level, but decreased with increasing saline water up to 50% level. Decrease in shootnumber of jojoba plant attributed to the negative effect of salt on bud formation and differentiation31.

Similar to growth and yield parameters, most of the yield quality parameters (excluding crude �ber content and antioxidant activity) of‘Koganesengan’ did not reveal a signi�cant difference among salinity levels. In contrast, irrigation salinity level had a substantial impact on ash,starch, ß-carotene, and ascorbic acid contents of ‘Beniazuma’. Salinity level did not affect dry matter, phenolic matter, protein, saccharose, glucose,and fructose contents of both varieties. In general, both crude �ber content and antioxidant activity of ‘Koganesengan’ were negatively affected byincreased salinity. However, it was reported that increased salt concentration caused signi�cant increases in antioxidant enzyme activities of sweetpotato varieties30. In contrast to yield parameters; ash, starch, and ß-carotene contents of ‘Beniazuma’ responded positively to increased salinity. Ina study with different varieties, Afaf et al.28 claimed that only the highest salinity level (50%) causes a signi�cant decrease in yield qualityparameters of all new tested cultivars including ‘Minu�ya 2/96’, ‘Minu�ya 6/96’ and ‘Minu�ya 171/96’, whereas ‘Mabrouka’ showed a signi�cantdecrease on these parameters under all salinity levels. They also stated that total carbohydrate, soluble sugar, and starch contents of sweet potatovarieties increased under low (10%), but decreased under moderate and high (30 and 50%) seawater levels. A similar result was also obtained byRodríguez-Delfín et al.29 that salinity stress signi�cantly increased the total amount of chlorophyll in the leaves of the 'Untacip', and proline contentin the leaves and tubers of ‘Huambachero’ and ‘Untacip’ varieties.

Although there was no signi�cant difference among salinity levels, signi�cant differences between varieties were found for some of the growth andyield quality parameters under different salinity level(s) and all yield parameters (except dry vine yield) only under control treatment. Because ofthese disparities, it may be concluded that ‘Beniazuma’ had higher values than those of the ‘Koganesengan’ in general. Similar conclusions werepropounded that the salinity response of some yield parameters varied signi�cantly among sweet potato varieties28,32,33. For example, Afaf et al.28

concluded that ‘Minu�ya 6/96’ was the most tolerant to the tested salinity stress, followed by ‘Minu�ya 2/96’ and ‘Minu�ya 171/96’, on the otherhand, Mabrouka cultivar was the most sensitive.

The linear models revealed that threshold salinity and slope values for fresh wine, tuber, and total yields of both sweet potato varieties were quitedifferent. The decreasing order for the threshold values of the yield parameters was ranked as fresh vine yield > total yield > tuber yield for‘Koganesengan’ and tuber yield > total yield > fresh vine yield for ‘Beniazuma’. The order (fresh vine yield > total yield > tuber yield) for the slopevalues of both cultivars was the same. Greig and Smith34 claim that sweet potato is a moderately sensitive plant with a threshold value of 1.5dS/m and 11% yield decrease after per salinity increment after threshold salinity for tuber yield. The slope value, in particular, differs from Greigand Smith34. The difference in threshold and slope values can be attributable to a range of factors, including variety, soil, water, and environmentalfactors, as well as cultural practices that in�uence the plant’s ability to tolerate salt. It is critical to highlight that in this study; saline irrigation waterapplications were realized under the drip irrigation method. However, salt tolerance lists published by the U.S. Salinity Laboratory35,36 representrelative tolerances when crops are grown under conditions that simulate recommended cultural and management practices (i.e. conventionalsurface irrigation with 15–20% leaching fraction) for the commercial production20. As a result, the lower slope value as an advantage in this studycould be attributed to more frequent irrigation realized using drip irrigation. Maas and Hoffman20 and Hanson et al.37 stated that frequent irrigationminimizes the in�uence of soil matric potential in salinity tolerance studies. Any cultural practices including frequent irrigation, land leveling,fertilization timing, and cultivation methods can be easily implemented as salinity management methods38. The salinity threshold and slopevalues from this study indicate that ‘Beniazuma’ is more sensitive to salt stress than the ‘Koganesengan’ variety.

ConclusionSalinity is an ever-present main constraint and a major threat to most crops, particularly in areas with irrigated agriculture. It is quite evident thatsalt stress has a considerable impact on the majority of crops. The level of salinity and solute concentration in the water, as well as the selectedcrop, determine the suitability of poor-quality water as a supplemental source for irrigation. Even varieties of the same species may demonstrate

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distinct responses to salt stress. The results of this study revealed that sweet potato varieties have quite different behaviors in terms of response tothe increasing salinity levels. Overall, the results suggest that, in general, the number of shoots and tubers, fresh vine yield, tuber yield, total yield,glucose content, and fructose content of ‘Beniazuma’ under non-saline treatment were higher than those of ‘Koganesengan’. In addition, increasedsalinity levels, in general, stimulated some yield quality parameters including ash, starch, ß-carotene, and ascorbic acid content of the ‘Beniazuma’variety. On the other hand, ‘Koganesengan’ has a better genetic potential to withstand salt stress, as revealed by their especially yield parameters,which were unaffected by increased irrigation water salinities. As a result, this study demonstrates that sweet potato growers in the Mediterraneanregion must consider both the salinity response function and productivity of these sweet potato varieties when using saline water under dripirrigation.

MethodsExperimental site and plant material. The study was conducted at the Agricultural Research and Implementation Area of Akdeniz University,Antalya, Turkey, under a polyethylene-covered rain-out shelter with uncovered sides. The geographic coordinate of the experiment area is 36° 53'15" N latitude and 30° 38' 53" E longitude with an average altitude of 54 meters. The Mediterranean climate dominates in the region, with hot anddry summer and moderate and wet winters. The long-term annual average temperature is 18.8°C, with January has the coldest averagetemperature of 10.0°C and a temperature difference (Tmax - Tmin) of 8.9°C, and July has the warmest average temperature of 28.4°C with atemperature difference of 11.4°C. The annual total precipitation is 1059 mm, with 538 mm falling between January and April, 61 mm between Mayand September, and 460 mm between October and December39.

In the experiment, ‘Koganesengan’ and ‘Beniazuma’ sweet potato varieties were used as plant materials. These varieties were developed in Japan in1966 and 1984, and they account for around 41% of the country’s sweet potato production. ‘Koganesengan’ is a high-yielding variety with high-starch content. The tubers are typically fusiform and have cream-colored skins with white to light yellow �esh. Mature leaves are cordate andsomewhat lobed.

‘Beniazuma’ variety is characterized by green cordate leaves with slight teeth on the margins. The tubers are fusiform, softly grooved, withappealing purple-red skin and golden �esh, and the vines are developing a dense canopy, purple in color and vigorous40,41. An adaptation study inTurkey’s Mediterranean region demonstrated that this plant may be produced with high yields14.

Table 1 shows some soil characteristics of the main parcels in the experimental area. The soils feature a sandy clay loam texture for the �rst 20cm and a clay loam texture for the next 20–40 cm of the soil depth. Soil bulk densities, �eld capacities, and wilting points on a dry weight basis themain parcels of ‘Koganesengan’ and ‘Beniazuma’ were ranged between 1.17–1.48 and 1.19–1.45 gr/cm3, 268–270 and 265–270 g/kg, and 130–133 and 127–131 g/kg, respectively.

Experimental design and treatments. In addition to the control treatment (S0 = 0.70 dS/m), four different irrigation water salinity concentrationsincluding low (S1 = 1.5 dS/m), medium (S2 = 3.0 dS/m), high (S3 = 4.5 dS/m) and very high (S4 = 6.0 dS/m) level were investigated in this study toreveal salinity response of the selected sweet potato varieties. The study was set up as a randomized complete block design for each varietybecause the soil parameters of the main parcels were essentially homogeneous (Table 1). As a result, the experimental area was divided into twomain parcels and each sweet potato variety was assigned to one of these. All irrigation water salinity levels were then randomly assigned to themain parcel of each variety. Each irrigation water salinity treatment had three replications. As a result, each main parcel with a single variety has 15sub-parcels. Each sub-parcel has three rows with a one-meter row spacing and a two-meter length. Each row bed has a width of 40 cm and a heightof 30 cm. The distance between sub-parcels was two meters. On May 20th, �ve plant vine shoots with four nodes were planted to row beds at 40cm distances by burying the two nodes of each vine shoot.

Drip irrigation lateral pipes were used to implement irrigation practices in each row bed. Throughout the experiment, all treatments were irrigatedwhen the control salinity treatment of each variety consumed 40 to 45% of the available water. The moisture sensors (Decagon, 5TE) were used tomonitor volumetric soil-water contents on a daily basis at 5, 15, 25, and 35 cm soil depths in the control salinity treatment parcels.

Throughout the study, sensor calibrations were carried out using soil moisture values obtained by the gravimetric method. For all treatments, thefollowing equation was used to compute the amount of applied water on a depth basis:

(1)where d is the amount of irrigation water to be applied (mm); Pvfc and Pvaw are the volumetric soil moisture at �eld capacity and available soilmoisture content before irrigation, respectively; D is the soil depth to be wetted (30 cm for both sweet potato varieties); P is the ratio of the area tobe wetted. The percent of the wetted area via drip irrigation was determined as 33% by using the approach given in Keller and Bliesner42.

In the study, irrigation water with an electrical conductivity of 0.70 dS/m was supplied via a hydrant. Except for control treatment, saline waters forthe other treatments were prepared by combining the calculated amounts of NaCl, CaCl2, and MgSO4 salt sources to achieve the desired salinity

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levels for each treatment while keeping sodium adsorption ratios (SAR) below 5.2 to avoid adverse effects of SAR on gas movement, soil structure,and water24,43.

Analyses and measurements. Considering the edge effect, the vine lengths, stem diameters, tuber lengths, and tuber diameters of the mid-threeplants in the second-row bed of each sub-parcel were measured by using a precise ruler and caliper at harvest at the end of the twentieth weekafter planting. The number of leaves, shoots, and tubers per plant were counted. The fresh and dry vine yields, tuber yields, and total yields werealso obtained. Tuber samples were analyzed for total dry matter44, ash and crude �ber45, starch46, phenolic matter47, ß-carotene45, ascorbic acid48,protein49, saccharose, glucose, and fructose50 contents and antioxidant activity51. Soil samples from each variety’s sub-parcel were collectedimmediately after harvest. These samples were sieved after drying in the open air. Using an EC and pH meter, electrical conductivities (ECe) and pHvalues (pHe) of the extracts obtained from saturated soil pastes were measured52.

Determining salinity threshold values. Using the salt tolerance model20 (Eq. 2) and a computer program53, the threshold soil salinity and the slopevalues of sweet potatoes for different yield components such as fresh vine, tuber, and total yields were determined.

Ya = 100 - b × (ECe - ECthreshould) 2where Ym and Ya are the maximum and actual dry yields (g/plant) from the control (non-saline) and the saline treatments, respectively; b is theslope value (% per dS/m); and ECthreshold and ECe are the threshold value and soil salinity beyond the threshold value (dS/m), respectively.

Statement on guidelines. All experimental procedures and �eld studies on plants comply with relevant institutional, national, and internationalguidelines and legislation.

Data analysis. All of the data were statistically evaluated by using analysis of variance (ANOVA) with SPSS 13.0 (SPSS Inc., Chicago, IL).Homogeneity and normality were checked before subjecting data to ANOVA. Unless otherwise noted, all statistical tests were performed at the 0.01level of signi�cance. If ANOVA reported signi�cant differences, treatment mean differences were separated using by Duncan’s multiple range testsat P ≤ 0.05.

DeclarationsAcknowledgements

This work was �nancially supported by the Scienti�c Research Projects Coordination Unit of Akdeniz University, Turkey (Project No. FBA-2017-2581).

Author contributions

KHD and AK conceived and designed the experiment; AK and KHD Performed the experiments and collected the data; CD and KHD Performed thelaboratory analyses; AK analyzed the data and interpreted the results; AK and KHD wrote the paper.

Competing interests

The authors declare no competing interests.

Additional information

Data Availability: The datasets generated during and/or analyzed during the current study are available from the corresponding author onreasonable request.

Correspondence and requests for materials should be addressed to A.K.

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TablesTable 1. Some characteristics of the experimental soils at main parcels.

Depth Koganesengan main parcels Beniazuma main parcels

BD FC WP Texture BD FC WP Texture

(cm) (g/cm3) (g/kg) (g/kg)

(g/cm3) (g/kg) (g/kg)

0-10 1.17 270 132 SCL 1.19 267 130 SCL

10-20 1.28 272 132 SCL 1.27 269 131 SCL

20-30 1.33 271 133 CL 1.28 270 129 CL

30-40 1.48 268 130 CL 1.45 265 127 CL

BD: bulk density; FC: �eld capacity; WP: wilting point; SCL: sandy-clay-loam; CL: clay-loam

Table 2. The effect of irrigation water salinity level on growth parameters of varieties

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Parameter Variety Salinity Level (dS/m)

S0 (0.70) S1 (1.5) S2 (3.0) S3 (4.5) S4 (6.0) Mean

ECe (dS/m)

Koganesengan 1.30† d‡A£ 2.82 cdA 4.95 cA 7.28 bA 9.13 aA 5.09 A

Beniazuma 1.23 eA 2.66 dA 4.80 cA 6.95 bA 9.54 aA 5.03 A

Mean 1.27 e 2.74 d 4.87 c 7.12 b 9.33 a

pHe

Koganesengan 7.79 aA 7.69 abA 7.64 abA 7.47 bA 7.47 bA 7.61 A

Beniazuma 7.76 abA 7.81 aA 7.71 abA 7.52 bcA 7.36 cA 7.63 A

Mean 7.78 a 7.75 a 7.67 a 7.49 b 7.41 b

Vine length (cm)

Koganesengan 75.57† aA 90.80 aB 83.90 aB 81.67 aB 88.97 aA 84.18 B

Beniazuma 94.77 aA 124.77 aA 107.33 aA 104.43 aA 98.67 aA 105.99 A

Mean 85.17 a 107.78 a 95.62 a 93.05 a 93.82 a

Stem diameter (mm)

Koganesengan 13.40 aA 13.03 aA 13.40 aA 13.27 aA 12.93 aA 13.21 A


Mean 13.53 a 12.93 a 12.88 a 13.07 a 13.07 a

Average tuber length (cm)



Mean 17.88 a 17.70 a 17.83 a 19.13 a 17.46 a

Average tuber diameter (mm)


Beniazuma 29.03 aA 25.83 aA 23.53 aA 24.80 aB 21.60 aA 24.96 B

Mean 29.43 a 28.15 a 24.48 a 28.40 a 24.77 a

Number of leaves (per plant)


Beniazuma 343.33 aA 219.10 aB 253.87 aB 257.90 aA 271.00 aA 269.04 B

Mean 321.12 a 288.72 a 310.55 a 258.38 a 277.05 a

Number of shoots (per plant)

Koganesengan 11.33 aB 12.90 aA 11.43 aA 8.43 aA 9.43 aA 10.07 A

Beniazuma 14.33 aA 9.47 bA 10.67 bA 8.33 bA 8.77 bA 10.31 A

Mean 12.83 a 11.18 ab 11.05 ab 8.38 c 9.10 bc

Number of tubers (per plant)

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Mean 6.47 a 7.05 a 6.78 a 5.38 a 7.18 a

†: Each value in italics is the mean of the three replications.

‡: Within each row (among salinity levels), means (in italic) followed by the same lowercase letter are not signi�cantly different at 5% levelaccording to Duncan’s multiple range tests.

£: Within each column (between varieties) of a parameter, means (in italic) followed by the same uppercase letter are not signi�cantly differentat 5% level according to Duncan’s multiple range tests.

Table 3. The effect of irrigation water salinity level on yield parameters


S0 (0.70) S1 (1.5) S2 (3.0) S3 (4.5) S4 (6.0) Mean

Fresh vine yield (t/ha)

Koganesengan 14.54† a‡B£ 19.07 aA 15.82 aA 12.14 aA 14.57 aA 15.23 A


Mean 21.21 a 15.79 b 14.44 b 12.70 b 13.33 b

Dry vine yield (t/ha)



Mean 3.22 a 2.71 a 2.49 a 2.14 a 2.29 a

Tuber yield (t/ha)



Mean 16.94 a 16.12 a 12.30 a 12.86 a 12.46 a

Total yield (t/ha)



Mean 38.15 a 31.91 ab 26.74 b 25.56 b 25.78 b




Table 4. The effect of irrigation water salinity level on yield quality parameters of varieties

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S0 (0.70) S1 (1.5) S2 (3.0) S3 (4.5) S4 (6.0) Mean

Dry matter content (g/kg)

Koganesengan 290.85† a‡A£ 292.06 aA 279.02 aA 283.23 aA 302.59 aA 289.55 A


Mean 295.40 a 288.63 a 289.17 a 289.12 a 305.72 a

Ash content (g/kg)

Koganesengan 43.43 aA 35.02 aA 30.62 aB 37.71 aA 40.53 aA 37.46 A

Beniazuma 34.46 bA 41.48 abA 48.66 aA 44.92 aA 31.91 bA 40.29 A

Mean 38.94 a 38.25 a 39.64 a 41.32 a 36.22 a

Crude �ber content (g/kg)

Koganesengan 29.21 aA 11.37 dA 22.67 bA 19.32 bcA 13.89 cdB 19.29 A

Beniazuma 13.22 aB 13.07 aA 16.97 aA 13.59 aA 18.55 aA 15.07 B

Mean 21.21 a 12.22 c 19.82 ab 16.46 bc 16.22 bc

Starch content (g/kg)

Koganesengan 658.26 aA 633.41 aB 651.69 aB 636.73 aB 657.30 aA 647.48 B

Beniazuma 643.68 bA 728.52 aA 729.34 aA 713.69 aA 706.16 aA 704.28 A

Mean 650.97 b 680.97 a 690.52 a 675.22 a 681.73 a

Phenolic matter content (mg GAE/kg)



Mean 7.57 a 8.50 a 8.80 a 7.15 a 7.49 a

Antioxidant activity (mg TE/kg)

Koganesengan 3490.68 aA 2101.17 bA 2179.54 bB 2007.31 bB 2434.85 bA 2442.71 B


Mean 3282.24 a 2545.34 a 2944.43 a 2666.77 a 2712.74 a

ß-carotene content (mg/kg)


Beniazuma 54.74 bA 58.75 bA 66.85 bA 58.73 bA 95.94 aA 67.00 A

Mean 59.58 a 49.57 a 73.15 a 76.27 a 87.72 a

Ascorbic acid content (mg/kg)

Koganesengan 37.03 aA 34.80 aA 27.70 aB 24.56 aB 36.21 aA 32.06 B

Beniazuma 47.26 abA 57.72 aA 40.69 abA 54.04 aA 30.47 bA 46.04 A

Mean 42.14 a 46.26 a 34.20 a 39.30 a 33.34 a

Protein content (g/kg)


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g g


Mean 61.01 a 59.47 a 59.69 a 60.91 a 59.45 a

Saccharose content (g/kg)



Mean 95.53 a 80.25 a 89.05 a 81.64 a 80.02 a

Glucose content (g/kg)



Mean 15.73 a 14.27 a 19.31 a 17.93 a 12.85 a

Fructose content (g/kg)



Mean 7.21 a 5.76 a 6.78 a 5.39 a 5.31 a




Figures

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Figure 1

Salt tolerance models for different yield components of sweet potato varieties

Salinity stress effects on growth and performance of drip ...

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