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Agricultural Water Management
journal homepage:www.elsevier.com/locate/agwatIdenti
fication of drought-tolerant pumpkin (Cucurbita pepo L.) genotypes
associated with certain fruit characteristics, seed yield, and quality
Musa Seymen
a, Duran Yavuz
b,⁎, Atilla Dursun
c, Ertan Sait Kurtar
a, Önder Türkmen
a aSelcuk University, Horticulture Department of Agriculture Faculty, Konya, TurkeybSelcuk University, Irrigation Department of Agriculture Faculty, Konya, Turkey cAtatürk University, Horticulture Department of Agriculture Faculty, Erzurum, Turkey
A R T I C L E I N F O Keywords: Breeding Pumpkin Water stress PCA A B S T R A C T
Climate change-associated drought stress in plants is one of the major environmental factors that cause a re-duction in plant growth, development, and productivity. Therefore, an improvement to obtain superior geno-types that are highly adaptable to arid and semi-arid conditions remains the main objective of the future breeding efforts. In this context, the present study was conducted to determine the genotypic differences among 16 inbred lines and 4 commercial cultivars of pumpkin associated with the parameters such as certain fruit characteristics, seed yield, and seed quality in irrigated and drought conditions. In the growing season of pumpkin, the amount of irrigation water applied was 402.6 mm in 2017 and 425.4 mm in 2018. In all the evaluated parameters, the examined genotypes exhibited a wide range of significant differences between the irrigated and drought conditions in both the years. Moreover, a significant positive correlation was observed between seed yield and fruit number, seed-thickness and plant height, and 1000-seed weight and seed size. In terms of seed quality, 1000-seed weight was determined to be a prominent parameter. The results of the present study demonstrated that these relationships imply a significant potential for the selection of genotypes with superior performance in both conditions. Furthermore, principal component analysis (PCA), performed con-sidering the Eigenvalues, indicated that the yield and quality components could be explained strongly by the PCA analysis in irrigated as well as in drought conditions. Finally, the inbred line G9 was observed to be the most superior genotype in terms of yield and fruit number in both irrigation and drought conditions; therefore, this inbred line is envisaged to be evaluated in future breeding studies and to be included in future hybrid programs in order to develop drought-tolerant cultivars.
1. Introduction
Climate change, rapid population growth, indiscriminate and ex-cessive consumption and a shortage of fresh and clean water resources have led to irrigation problems (Rijsberman, 2006). Plants exposed to arid conditions must be capable of adapting to such environmental conditions or adapt to water stress in order to serve as economically viable crops (Shubha and Tyagı, 2007). Therefore, using the genotypes with a higher ability to adapt to arid conditions has been established as the main criterion in the breeding efforts for the development of novel drought-tolerant cultivars (Akashi et al., 2005;Karipçin et al., 2009). With an increase in arid and semi-arid areas in the world, there is an increasing inclination toward the cultivation of plants such as appeti-zers squash which is able to utilize water effectively and economically. Despite increased production, the maintenance of desired commercial
qualities in a cultivar remains one of the most important constraints encountered in thisfield. Therefore, it is required that drought-tolerant genotypes be identified in order to allow the development of tolerant cultivars to meet the food demand of the future world.
Cucurbita pepo, C. moschata, and C. maxima constitute economically important species of the Cucurbitaceae family which are cultivated throughout the world. Among these species, C. pepo is used in human nutrition. The mature seeds and flowers of the plants of the afore-mentioned species have been used as well, in addition to the con-sumption of its fruit. Pumpkin seeds contain 28%–40% protein (Achu et al., 2005) and 35%–50% fat, out of which 78% are unsaturated fatty acids (Seymen et al., 2016;Türkmen et al., 2015). Pumpkin seeds are a source of vitamin A, C, and E (Eleiwa et al., 2014;Ghanbari et al., 2007; Ondigi et al., 2008) and are rich in mineral substances such as po-tassium, phosphorus, calcium, magnesium, and iron, which are
https://doi.org/10.1016/j.agwat.2019.05.009
Received 7 March 2019; Received in revised form 3 May 2019; Accepted 4 May 2019
⁎Corresponding author.
E-mail address:dyavuz@selcuk.edu.tr(D. Yavuz).
Available online 08 May 2019
0378-3774/ © 2019 Elsevier B.V. All rights reserved.
important for human nutrition (Seymen et al., 2016).
Pumpkin seeds, in addition to being consumed as an appetizer, are used as food additives in several products such as bread, salami, sau-sage, and mayonnaise because of their high protein content (Mansour et al., 1993;Rangahau, 2002). Moreover, pumpkin seeds are produced for medicinal purposes in Russia and certain African countries (Murkovic et al., 1996). Pumpkin seeds contain significant levels of antioxidants (tocopherols and tocotrienols), which have been reported to reduce the risk of certain types of cancers such as gastric, breast, lung, and colorectal cancers (Lee et al., 1999;Goodman et al., 2004; Nesaretnam et al., 2007;Stevenson et al., 2007; Lelley et al., 2009). Furthermore, pumpkin seeds have been reported to be rich in phytos-terols which play a key role in lowering the cholesterol levels and in reducing benign prostate hyperplasia (Gossell-Williams et al., 2006; Fruhwirth and Hermetter, 2007; Hong et al., 2009; Thompson and Grundy, 2005). Owing to their constituents, the pumpkin seeds have been reported to exert promotive and protective effects on the human immune system (Chew and Park, 2004).
The production of pumpkin has been observed to be increasing, due to reasons such lesser water requirement compared to several other agricultural species, ability to grow in absence of irrigation in certain areas which receive sufficient rainfall and in rotation with the field crops, harvest ease, availability of mechanized cultural processes, ability to be relatively resistant to diseases and pests, and no require-ment for storage. Pumpkin also exhibits a higher economic yield in arid and semi-arid regions compared to other agricultural products such as wheat, barley, and chickpeas.
The objective of the present study was to identify drought-tolerant pumpkin lines associated with yield, fruit, and seed characteristics through an experimentation conducted for two years in irrigated as well as non-irrigated conditions with 20 pumpkin genotypes. The superior drought-tolerant pumpkin cultivar candidates selected as a result of the study would also contribute to the gene pool for future breeding efforts for the development of drought-tolerant hybrid pumpkin cultivars.
2. Materials and methods
2.1. Soil and climate characteristics of the experimental area
The present study was conducted during the months of May and September in years 2017 and 2018, at the Faculty of Agriculture, Selcuk University, Konya, located at 38°05′N, 32°36′E at an altitude of 1006 m, in central Anatolia, Turkey. Konya is an area which is agriculturally important and comprises approximately 1.9 million hectares of arable land, which constitutes 8% of the total agricultural land assets in Turkey. According to long-term climate data, Konya Plain has an arid and semi-arid climate and the total amount of annual rainfall received in this region is only 320 mm; of which, only 90–100 mm of rainfall occurs during the plant-growing season (May–September). In addition, the evaporation observed in the region in the plant-growing season is greater than 1000 mm (Fig. 1). Therefore, irrigation becomes a ne-cessity for crop production in this area.
In the present study, certain climatic parameters such as tempera-ture, relative humidity, wind speed, and precipitation were measured and recorded on an hourly basis by using a portable automated weather station (Davis Vantage Pro 2) located at the center of the study area. The total amount of precipitation during the period between the sowing of the pumpkin seeds and their harvest as observed in the present study was approximately 90 mm in 2017 and 70 mm in 2018. The tempera-ture reached 40 °C and the relative humidity dropped to 35%, especially in the months of July and August. The average wind speed during the study period was between 2.5–3 m/s. The climate data for the experi-mental years (2017 and 2018) were in accordance with the long-term average climate data available for the region.
The soil of the study area has a silty–clayey–loamy texture. The organic matter content present in 0–90 cm of the soil profile, pH, and
the bulk density values of the soil in the study area ranged from 1.43% to 2.16%, 7.44–7.50, 1.28–1.32 g/cm3
, respectively. The value of total available water (TAW) in the upper 90 cm of the soil profile in the study area was 140.7 mm. There is no hurdle in the pumpkin cultivation in terms of physical and chemical properties of the soil in the studied region.
2.2. Plant material, planting, and irrigation
In the present study, pumpkin genotypes that were collected from different regions of Turkey were used as plant material. The pumpkin genotypes were self-pollinated for several years to reach the S7 level. Subsequently, 16 inbred lines that exhibited superior agronomic traits were selected from the collected gene pool. In addition, two-hybrid (G1: Mertbey F1 and G2: Senahanim F1) and two local cultivars (G3: Hatuntırnağı and G4: Cercevelik) with high commercial value in the market were used to serve as control group.
The present study was conducted using a randomized block design with three replicates, in full-irrigated and complete-stress (drought) conditions. Each parcel, consisting of 4 plant rows, was designed in 4 × 5 m plots, and the parcels were arranged 2 m from each other and 2.5 m from the blocks. A total of 40 pumpkin seeds were sown by hand with 1 m row spacing and 0.5 m inter-row spacing within each parcel. In the present study, a drip irrigation system was utilized to irrigate the plots belonging to the irrigation group. Round drip irrigation pipes of 5 m length, 16 mm diameter, and 4 L/h discharge rate at a pressure of 100 kPa were placed for each plant row. Drippers at the lateral pipes were arranged at a distance of 50 cm from each other in consideration with the soil characteristics. The lateral pipes were connected to the manifold pipes each with a diameter of 40 mm, and the manifold pipes were connected to the PE main pipe with a diameter of 63 mm. The amount of irrigation water required to be applied to the irrigated plots was calculated using Eq.(1), in consideration of the amount of cumu-lative water evaporation which was obtained from the Class A-type pan installed in the study area, at seven-day intervals. In the programmed irrigation, irrigation water was applied ten times to the experimental subjects belonging to the irrigation group at seven-day intervals. In the growing season of pumpkin, the total amount of irrigation water ap-plied was 402.6 mm in 2017 and 425.4 mm in 2018 (Table 1).
I = Ep× Kp× Kc× A (1)
where
I = Amount of irrigation water (liters) A = Parcel area (m2)
Ep= Cumulative pan evaporation (mm) [measured using standard
Class A pan during an irrigation period of seven days]
Kp = Pan coefficient [a value of 0.82 recommended by Yavuz
(2016)was used)]
Kc= Plant coefficient [The Kcvalues recommended for pumpkin by
Fig. 1. The relationship between precipitation and evaporation according to the climate data of the region for years 1960–2016.
Yavuz et al. (2015)were used]
On the basis of soil analyses, all plots received the same amount of the total fertilizer. A compound fertilizer was applied (100 kg ha−1N, 100 kg ha−1P2O5, and 100 kg ha−1K2O) at planting. The rest of N
fertilizer was applied during fruit set period at a rate of 50 kg ha―1. Throughout the developmental period of the plants, cultural practices such as cultivation, weed control, diseases management, and pest management were conducted regularly. Twenty days prior to the har-vest time, irrigation was discontinued in the fully-watered plots. Post complete drying of the plants, fruits were harvested and mature seeds were extracted from these fruits.
2.3. Fruit and seed measurements
Plant length was measured at 20-day intervals in the period between flowering and the commencement of stress. The fruits were harvested, except in the cases of edge effects, on 27 September 2017 and on 25
September 2018. The fruit number per plant was determined in pro-portion to the plant number in each parcel. Fruit width and length were measured using a large digital caliper, and fruit weights were recorded using a digital scale. Subsequent to fruit harvest from the parcel, seeds were extracted from the harvested fruits and dried under shade. Subsequently, seed yield in each parcel was determined. Seed width, seed length, and seed thickness were measured in 20 seeds selected from each parcel by the digital caliper. The 1000-seed weights were also determined for each parcel using the digital scale.
2.4. Evaluation of data
The combined variance analysis performed for the yield and quality components obtained for both the trial years (2017 and 2018) was examined using homogeneity tests. According to the results of the homogeneity tests, the experimental years required to be evaluated separately as the values of yield and quality parameters were not homogeneous in terms of error variance of the years. The fruit char-acteristics, seed yield, and the quality parameters were subjected to analysis of variance, and the results were considered statistically sig-nificant at 1% and 5% significance levels according to Duncan’s test (Yurtsever, 1984;Düzgüneş et al., 1987). The analysis of variance and correlation tests were performed using the SPSS 22.0 packaged soft-ware.
The present study was aimed to interpret several yield and quality parameters in combination. Therefore, Principal Component Analysis (PCA) was utilized for a multivariate statistical analysis, which allowed a considerable reduction in the number of parameters required to ex-plain most of the data. In this manner, the values for seed yield, seed characteristics, and fruit characteristics obtained from the averages of results of the two experimental years in the irrigated and drought conditions were subjected to PCA, separately, using the JMP 10 sta-tistical program.
Table 1
The amount of irrigation water and irrigation date.
2017 2018
Irrigation Date Irrigation Water (mm) Irrigation Date Irrigation Water (mm) 12 May 25.0 14 May 25.0 26 June 30.1 28 June 28.3 3 July 39.0 4 July 34.8 11 July 39.6 11 July 42.5 18 July 55.3 19 July 65.4 25 July 52.2 26 July 48.3 1 Aug 53.0 1 Aug 42.1 7 Aug 19.5 8 Aug 48.3 15.Ağu 38.4 15 Aug 30.4 22 Aug 24.0 21 Aug 27.7 28 Aug 26.7 29 Aug 32.5 Total 402.6 Total 425.4 Table 2
Mean squares from the analysis of variance of the seed yield, fruit and seed characteristics under the irrigation and drought conditions in 2017 and 2018.
Years Component Error mean Squares (df:38) CV (%) Genotype (Mean Squares) (df:19) Irrigated Drought Irrigated Drought Irrigated Drought 2017 SY 1239.23 91.486 20.3 25.9 6470.01** 1669.14** NF 0.036 0.026 15.1 22.9 0.154** 0.368** MFW 0.217 0.031 16.6 19.0 1.465** 0.365** PH 90.355 66.735 18.6 28.1 1819.67** 515.22** FL 4.453 2.598 9.7 11.7 81.062** 23.402** FW 1.944 1.040 7.9 8.6 15.639** 5.448** TSW 1120.98 353.39 13.6 10.0 6041.37** 3071.60** ST 0.073 0.086 8.4 9.5 0.171* 0.321** SL 1.448 1.049 5.8 5.5 8.620** 9.769** SW 0.428 0.307 6.2 5.7 3.534** 4.982**
Years Component Error mean Squares (df:38) CV (%) Genotype (Mean Squares) (df:19) Irrigated Drought Irrigated Drought Irrigated Drought 2018 SY 814.256 164.065 17.5 22.5 3730.99** 630.84** NF 0.04 0.032 15.9 26.5 0.112** 0.125** MFW 0.153 0.045 15.2 27.4 1.092** 0.127** PH 55.633 49.606 11.0 15.0 3372.07** 2936.73** FL 8.722 3.260 14.9 12.5 53.401** 34.87** FW 2.425 3.673 8.8 15.5 10.423** 6.952* TSW 693.114 632.14 10.4 13.4 3827.25** 2436.24** ST 0.037 0.064 6.0 9.0 0.185** 0.176** SL 0.666 1.069 4.1 5.7 3.431** 5.433** SW 0.549 0.410 7.3 6.9 1.819** 1.847**
Seed yield (SY); Number of fruit (NF); Mean fruit weight (MFW); Plant height (PH); Fruit length (FL); Fruit width (FW); Thousand seed weight (TSW); Seed thickness (ST); Seed length (SL); Seed width (SW).
* Statistically significant according to P < 0.05. ** Statistically significant according to P < 0.01.
3. Results and discussion
3.1. Effect of drought stress on seed yield and plant length
Seed yield, fruit number, and plant length of the pumpkin genotypes were observed to be statistically significant (P < 0.01) in both irri-gated and drought conditions for both the experimental years (Table 2). When considering the seed yields in the irrigated plots, G1, G2, G9, G11, and G31 produced the highest yield and were statistically in the same group (Table 3).
While G2, with an average yield of 2067 kg ha–1, was the best commercial variety among the hybrids, the G9 and G31 inbred lines exhibited approximately 6% (2202 kg ha–1) and 1% (2114 kg ha–1) higher yields, respectively, in comparison to the commercial cultivars in irrigated plots. The aforementioned genotypes were, therefore, en-visaged as the inbred lines which could serve as candidates for selection as the commercial variety in irrigated conditions.
In full-irrigated conditions, the pumpkin seed yield observed in a study conducted in Iran was 1700 kg ha–1(Ghanbari et al., 2007), in Egypt, was 930 kg ha–1(Amer, 2011), and in Turkey was 1100–1200 kg ha–1(Yanmaz and Düzeltir, 2004). It is obvious that the yield obtained in the present study was higher than the yields reported by the previous studies. These higher yields could be caused by factors such as climate, soil characteristics, genotype, planned irrigation program, and drip ir-rigation method. The drought stress resulted in about 80% reduction in the seed yield across the two seasons (2017 and 2018). Drought stress was observed to exert different effects on the seed yield in the two experimental years: the highest yield in thefirst year was obtained from G9 and G34, while the highest yield in the second year was obtained from G2, G11, G13, G14, G16, G22, and G40.
In dry conditions, the commercial cultivars G1 and G2 exhibited higher yields compared to the standard cultivars, while among the inbred lines it was G9 and G34 that produced higher yields relative to the commercial cultivars. Therefore, the aforementioned genotypes were considered to be the superior inbred lines which could be used for the improvement of tolerant hybrid cultivars in the arid and semi-arid regions (Table 3). Several physiological factors have been observed to be adversely affected by drought, and the drought that occurs during
theflowering period causes severe loss of yield (Farooq et al., 2009). According to the result of a previous study conducted in the Konya province, drought resulted in severe loss of pumpkin yield (Yavuz et al., 2015). Moreover, seed yield ranging from 500 to 1270 kg ha–1at dif-ferent irrigation levels and deficit irrigation exerting negative effects on the yield of pumpkin have been reported in a previous study (Cakir, 2000).
When both the experimental years are evaluated in terms of seed yield, the genotypes were divided into four categories which differed in their differential yield analysis diagram (Fig. 2) (Fernandez, 1992). In this diagram, thefirst category identified high yielding genotypes in irrigated as well as non-irrigated conditions and included G1, G2, G9, G11, G13, G22, G32, and G40. The second category contained high yielding genotypes in the irrigated conditions and low yielding geno-types in the non-irrigated conditions such as G3, G28, G30, and G31. The third category identified high yielding genotypes in the non-Table 3
Seed yield and number of fruits under irrigation and drought conditions in 2017 and 2018.
Genotype Seed yield (kg ha−1) Number of fruits
2017 2018 2017 2018
Irrigated Drought Irrigated Drought Irrigated Drought Irrigated Drought G1 1885a−d 654b 1815a−e 285def 1.13cde 1.05abc 1.11c−f 0.42de
G2 2090abc 337def 2045abc 517ab 1.04cde 0.48d 1.14c−f 0.69a−d
G3 1970a−d 165fgh 1564c−g 209efg 1.09cde 0.35d 1.20b−f 0.48cde
G4 1567cde 198e−h 1436d−g 80g 1.07cde 0.39d 0.96ef 0.29e
G8 1114ef 176fgh 1368d−g 201efg 1.20cde 0.43d 1.27a−f 0.89ab
G9 2525a 851a 1880a−d 422bcd 1.67ab 1.24a 1.49abc 0.68a−d
G11 1844a−d 276d−g 1830a−d 553ab 1.00de 0.22d 1.29a−f 0.60b−e
G13 1782b−e 339def 2236ab 591a 1.39abc 0.91bc 1.56ab 0.98a
G14 1152ef 418cd 1711b−f 510ab 1.29cde 1.20ab 1.42a−d 1.03a
G16 1125ef 377de 1105g 470abc 1.37a−d 1.00abc 1.21b−f 0.98a
G22 1560cde 306def 2308a 532ab 0.94e 0.49d 1.61a 0.80abc
G25 1304def 120gh 1233hg 257ef 1.25cde 0.33d 1.34a−e 0.54cde
G26 773f 291d−g 1266efg 282def 1.05cde 0.98abc 1.07def 0.75a−d
G28 2173abc 112gh 1493c−g 173fg 1.69a 0.28d 0.92f 0.42de
G30 2413ab 265d−g 1689b−f 349cde 1.11cde 0.48d 1.12c−f 0.77a−d
G31 2196abc 82h 2033abc 208efg 1.14cde 0.33d 1.15c−f 0.62b−e
G32 1850a−d 633b 1529c−g 355cde 1.33bce 1.00abc 1.30a−f 0.74a−d
G34 1950a−d 902a 1249hg 345cde 1.33bce 0.96abc 1.15c−f 0.53cde
G40 1925a−d 557bc 1697b−f 542ab 1.25cde 1.07abc 1.27a−f 0.76a−d
G45 1566cde 322def 1183hg 245ef 1.71a 0.85c 1.56ab 0.51cde
Mean 1738 369 1633 356 1.25 0.70 1.26 0.67
Lower-case letters indicates significantly different according to P < 0.05.
Fig. 2. Scattergram showing the identification and categorization from yield of twenty pumpkin genotypes grown in the irrigated and drought conditions.
irrigated conditions and low yielding genotypes in the irrigated con-ditions, which comprised G14, G16, and G34. G4, G8, G25, G26, and G45 were located in the fourth category which identified the low yielding genotypes in both irrigated and non-irrigated conditions.
It is well known from several previous reports that different geno-types respond differently to dry conditions (Ongom et al., 2016;Darkwa et al., 2016; Mohammadi and Abdulahi, 2017). Therefore, the de-termination of genotypes that are tolerant to dry conditions is crucial in thefield of agricultural research. According to the findings of the pre-sent study, G9 and G34 genotypes, which exhibited highest yields in dry conditions, have been proposed as superior genotypes for arid and semi-arid areas having limited water resources.
According to the literature, by using the differential yield analyses diagram, 12 genotypes in bean (Darkwa et al., 2016), 7 genotypes in wheat (Mohammadi and Abdulahi, 2017), and 5 genotypes in rice (Aminpanah et al., 2018) have been determined as drought-tolerant cultivar candidates.
Fruit number is a parameter that has been associated directly with the yield. In thefirst year, the average fruit number observed in the irrigated plots was 1.25, while the fruit number observed in the drought conditions was 0.7. Similarly, in the second year, the fruit number obtained in the irrigated and the non-irrigated conditions was 1.26 and 0.67, respectively. G9 and G45 exhibited the highest fruit number per plant in the irrigated conditions. In this respect, G9, G13, G14, G16, G26, G32, and G40 exhibited the highest values in dry conditions, for both the experimental years (Table 3). In a previous study, drought stress was observed to be directly related to yield, and the fruit number per pumpkin plant observed in that study was 1.2 (Seymen et al., 2012). Furthermore, the fruit number has been observed to decrease in pepper (Jeeatid et al., 2018) and cucumber (Najarian et al., 2018) as a result of drought stress.
Plant length is an important factor in pumpkin production. Certain pumpkin genotypes have lateral branches, while others have compact (branchless) structures. In the present study, the plant lengths of all the genotypes investigated were adversely affected by dry conditions (Table 4). G28 genotype was the one to exhibit the longest branches in irrigated and non-irrigated conditions in both the experimental years. According to the literature, drought has been observed to exert a
negative effect on the plant height in melon (Cucumis melo L.) (Kuşvuran and Abak, 2012) and has also been reported to cause a 31%-decrease in the plant height in wild barley genotypes (Tyagi et al., 2011).
3.2. Effect of drought stress on certain fruit characteristics
The effects of irrigated and drought conditions on fruit weight, fruit length, and fruit width of a few pumpkin genotypes were observed to be statistically significant in both the experimental years (P < 0.01 for 2017 and P < 0.05 for 2018) (Table 2).
In thefirst year, the average fruit weight obtained under irrigated conditions was 2.81 kg and the average fruit weight in drought condi-tions was 0.93 kg, implying that the drought caused 67% reduction in fruit weight. Similarly, in the second year, the average fruit weights obtained in the irrigated and drought conditions were 2.58 kg and 0.77 kg, respectively, implying that the fruit weight decreased by 70% in drought conditions.
While the dry conditions in theflowering period in pumpkin caused a 37%-reduction in the fruit weight, the reduction observed was 67% in the fruit-set period (Masoodi and Hakimi, 2017). The heaviest fruits obtained were from the G11 and G22 genotypes in the irrigated as well as in drought conditions for both the experimental years (Table 4). Similar to thefindings of the present study, fruit weights reported in previous studies were 2.67 kg (Seymen et al., 2011), 3.06 kg (Türkmen et al., 2016), and 3.48 kg (Masoodi and Hakimi, 2017) in irrigated conditions and deficit irrigation was reported to exert a negative effect on the fruit weight in pumpkin (Ertek et al., 2004).
Arid conditions in the present study were observed to exert negative effects on fruit length, and the fruit length was observed to decrease by 37% in thefirst year and by 28% in the second year. Similarly, the decrease in the fruit width was 33% and 30% in thefirst and second year, respectively. In a previous study, drought was observed to cause a 14% decrease in the fruit length and a 25% decrease in the fruit width in pumpkin (Yavuz et al., 2017).
While G32, G34, G40, and G45 lines exhibited the highest values for fruit width, different genotypes were observed to exhibit different re-sponses for fruit length in the irrigated as well as drought conditions for
Table 4
Mean fruit weight and plant height under irrigation and drought conditions in 2017 and 2018.
Genotype Mean fruit weight (kg) Plant height (cm)
2017 2018 2017 2018
Irrigated Drought Irrigated Drought Irrigated Drought Irrigated Drought G1 2.07fg 0.72de 2.12e−h 0.57cde 23.2h 17.8d 29.2j 19.3h G2 2.35efg 0.67de 2.58c−f 0.77b−d 47.3d−g 26.2bcd 70.9de 41.5c−f G3 2.86c−f 0.67de 2.29efg 0.54de 50.0def 35.6bc 143.0a 94.5a G4 3.09b−e 0.77de 3.19abc 0.77b−d 64.4cd 37.3b 83.3cd 50.2c G8 2.33efg 0.72de 2.56c−f 0.78b−d 32.7fgh 19.9cd 44.1hı 25.6gh G9 2.73def 0.91cd 2.41d−g 0.75b−d 98.4b 56.8a 102.3b 90.5a G11 3.47a−d 1.80a 3.66a 1.02ab 42.4efg 21.9bcd 51.2ghı 28.3fgh G13 2.01fg 0.91cd 2.21e−h 0.97abc 31.9fgh 21.6bcd 40.2ıj 22.6gh
G14 2.20efg 0.71de 2.25efg 0.63b−d 41.1e−h 18.7d 47.4ghı 29.1e−h
G16 2.01fg 0.59de 1.70gh 0.75b−d 34.0fgh 17.6d 37.1ıj 29.5e−h G22 3.83ab 1.70a 3.78a 1.34a 56.3cde 24.8bcd 72.1de 42.0cde G25 2.60d−g 0.74de 2.67b−e 0.94b−d 69.6c 33.8bcd 149.6a 83.27b G26 2.73def 0.89cd 2.51c−f 0.66b−d 28.8gh 19.6cd 38.8ıj 25.7gh G28 2.39efg 0.77de 1.90fgh 0.56cde 123.5a 68.2a 140.0a 88.6a G30 3.40a−d 1.16bc 3.35ab 1.03ab 30.7gh 24.2bcd 39.2ıj 25.7gh G31 4.05a 0.70de 2.61c−f 0.65b−d 37.9fgh 22.0bcd 54.2fgh 35.2d−g G32 3.88ab 1.12bc 3.15a−d 0.78b−d 56.0cde 31.0bcd 65.1ef 45.7cd G34 2.82c−f 1.17bc 2.49c−f 0.70b−d 41.6efg 25.6bcd 46.7ghı 29.8e−h G40 3.68abc 1.30b 2.71b−e 0.78b−d 68.3c 35.0bc 89.3c 50.7c
G45 1.78f 0.54e 1.50h 0.47e 45.2efg 23.2bcd 59.2efg 31.8e−h
Mean 2.81 0.93 2.58 0.77 51.20 29.08 67.76 46.92
both the experimental years (Table 5). Therefore, the average fruit length and fruit width of the pumpkin genotypes were determined as 20.07 cm and 17.31 cm, respectively, in the irrigated plots (Seymen et al., 2011). Full-irrigation conditions have been observed to exert positive effects on the fruit number, fruit lenght, and fruit width in previous studies; on the contrary, deficit irrigation has been observed to exert negative effects on the fruit characteristics (Ertek et al., 2004). 3.3. Effect of drought stress on seed quality
The effects of irrigated and drought conditions on 1000-seed weight, seed thickness, seed length, and seed width of certain pumpkin genotypes were observed to be statistically significant at P < 0.01 and P < 0.05 levels in 2017 and 2018, respectively (Table 2).
Seed width (SW) is a parameter that is directly related to yield in pumpkin. Large and full seeds are related to enhanced yield and seed quality and are desirable among producers and consumers.
In thefirst year, the average 1000-seed weight obtained in the ir-rigated conditions was 246 g, while it was 188 g in the drought con-ditions, implying that the 1000-seed weight decreased by 24% in the arid conditions. In the second year, the irrigated and non-irrigated plots exhibited 253 g and 187 g of average 1000-seed weight, respectively, implying a decrease of 26% in arid conditions.
The lines G4, G11, G22, G30, and G34 produced the highest 1000-seed weight in the irrigated, as well as drought conditions for both the experimental years and these genotypes were in the same group sta-tistically. Previous studies have reported a wide range of 1000-seed weights in pumpkin in irrigated conditions, for example, 134 g (Warid et al., 1993), 178 g (Türkmen et al., 2014), 203 g (Joshi et al., 1993), and 239 g (Türkmen et al., 2016). Similarly, drought application in the fruit-set period of pumpkin has been reported to cause a decrease of 27% in the 1000-seed weight (Masoodi and Hakimi, 2017). When compared to the irrigated conditions, drought stress was observed to exert a negative effect on seed thickness, which was reduced by 4% in thefirst year and by 14% in the second year. G11 exhibited impressive seed thickness values in the irrigated as well as drought conditions for both the experimental years (Table 6).
In thefirst year, the average seed length recorded was 20.71 mm in
the irrigated plots, while it was 18.52 mm in the drought conditions, implying that the seed length was reduced by 11%. Similarly, the seed length values recorded in the second year were 19.86 mm and 18.52 mm in the irrigated and non-irrigated plots, respectively, im-plying that the drought caused 10% reduction in the seed length in the second year. Similar to thefindings of the present study, drought stress was observed to result in a 12% reduction in the seed length and 10% reduction in the 1000-seed weight in pumpkin (Yavuz et al., 2017).
The seeds are the consumable part of pumpkin, which is why longer seeds are desirable in relation to seed quality as it facilitates cracking. G3, G11, and G34 exhibited the highest values for seed length and seed quality, and were, therefore, regarded as the superior genotypes in ir-rigated as well as drought conditions for both the experimental years. Moreover, drought also affected the seed width negatively and caused a decrease of 7% in thefirst year and 8% in the second year. The highest seed width value was obtained for G11 and G32 in both the experi-mental years (Table 7).
Similar to the results of the present study, the values for seed length and seed width recorded were 20.05 mm and 10.92 mm, respectively, as reported in a study byTürkmen et al. (2016), and 16.91 mm and 8.67 mm as reported by another study byJoshi et al. (1993). Moreover, thefindings ofParis and Nerson (2003)demonstrated a wide range of seed length (from 8.8 to 23.3 mm), seed width (from 5.0 to 12.5 mm), and seed thickness (from 1.2 to 3.8 mm) in pumpkin.
3.4. Correlation between parameters
When the correlation between the yield and the quality parameters was evaluated (P < 0.01), a significant positive correlation was ob-served between seed yield and fruit number (r = 0.715**) in drought conditions. Fruit length was observed to be positively correlated with fruit weight (r = 0.602**) and plant height (r = 0.685). Moreover, it was determined that the 1000-seed weight had a positive relationship with seed thickness, seed length, seed width, plant height, and fruit length. A similar positive and strong relationship was also determined among seed width, plant height, and fruit length (Table 8). Correla-tively, it has been reported in a previous study that seed size exhibits a positive relationship with fruit size and seed shape in Cucurbita pepo Table 5
Fruit length and fruit width under irrigation and drought conditions in 2017 and 2018.
Genotype Fruit length (cm) Fruit width (cm)
2017 2018 2017 2018
Irrigated Drought Irrigated Drought Irrigated Drought Irrigated Drought G1 23.27de 14.73b−f 24.53abc 15.53c−f 14.60jk 10.77e−h 14.77f 10.20bcd
G2 20.50efg 12.27d−g 21.07b−g 15.97cde 16.03g−k 10.03gh 18.57abc 12.63bcd
G3 21.70ef 13.00d−g 17.20fgh 12.23fg 17.70d−h 11.70d−g 17.00b−f 11.00bcd
G4 20.97ef 12.27d−g 20.73b−g 12.83efg 19.33b−e 12.63a−e 20.30a 12.97a−d
G8 17.60fgh 11.77efg 17.30fgh 12.57efg 17.40e−h 11.30efg 17.87a−e 12.13bcd
G9 19.73efg 12.83d−g 18.73d−h 13.10efg 18.67c−f 12.43b−f 18.23a−d 12.87bcd
G11 31.20ab 15.20bcd 25.93ab 19.83ab 15.90h−k 13.70abc 16.40c−f 16.50a
G13 20.33efg 16.17bc 23.10a−e 17.53bc 13.97k 10.47fgh 15.47def 12.50bcd
G14 15.57h 10.87gh 14.73hı 10.97g 18.20d−h 11.63d−g 17.20b−f 12.03bcd
G16 21.6ef 15.20bcd 23.60a−d 17.20bc 14.60jk 9.30h 15.00ef 12.07bcd
G22 28.93bc 20.87a 20.13c−h 17.27bc 17.03e−ı 12.37b−f 19.57ab 14.27ab
G25 26.07cd 14.83b−e 22.83a−f 17.90abc 15.73ı−k 11.37efg 14.40f 9.27d
G26 19.97efg 13.93c−g 19.17c−h 13.70d−g 18.57c−g 12.00c−g 18.23a−d 12.13bcd G28 20.63efg 13.63c−g 17.23fgh 11.30g 17.33e−h 11.70d−g 16.60b−f 11.43bcd G30 26.47cd 17.53b 27.17a 20.90a 17.43e−h 11.33efg 17.10b−f 12.13bcd G31 32.70a 16.70bc 22.77a−f 16.70bcd 17.70d−h 11.00e−h 17.17b−f 12.43bcd G32 21.17ef 13.77c−g 17.00gh 12.03g 22.23a 13.37a−d 20.20a 13.33abc G34 16.83gh 10.87gh 14.67hı 10.70g 21.03abc 14.13ab 20.40a 13.27abc
G40 17.87fgh 11.63fg 17.60e−h 13.03efg 21.30ab 14.53a 18.93abc 13.27abc
G45 11.67ı 8.13h 10.20ı 7.57h 20.17a−d 12.70a−e 19.53ab 10.73bcd
Mean 21.74 13.81 19.79 14.44 17.75 11.92 17.65 12.36
(Paris and Nerson, 2003).
A positive correlation was also determined between seed thickness, seed yield, and fruit length under irrigated conditions in the present study. Similar to drought conditions, 1000-seed weight demonstrated a positive relation with fruit length, seed thickness, seed length, and seed width in the irrigated conditions as well. On the other hand, fruit weight was observed to have a negative relationship with fruit number and plant height. There was a weak positive relationship between the seed yield and the 1000-seed weight (Table 9). Similarly, seed yield per fruit and seed size have been reported to demonstrate a weak correla-tion in pumpkin (Berenji and Papp, 2000). A positive relationship was
observed between seed number and seed weight per fruit (r = 0.92–0.93) and between seed weight and seed size (r = 0.49) in a study byWarid et al. (1993). According to thefindings of the present study, no relationship existed between the fruit weight and the 1000-seed weight in both irrigated and drought conditions. A strong re-lationship was observed between 1000-seed weight and seed size, which confirmed 1000-seed weight as a prominent parameter in terms of seed quality. On the other hand, compared to irrigated conditions, fruit number was identified as the decisive parameter in terms of seed yield in arid conditions, which corroborated thefinding that the gen-otypes that exhibited higher fruit number produced a greater yield. Table 6
1000-seed weight and seed thickness under irrigation and drought conditions in 2017 and 2018.
Genotype 1000 seed weight (g) Seed thickness (mm)
2017 2018 2017 2018
Irrigated Drought Irrigated Drought Irrigated Drought Irrigated Drought G1 226.1c−f 189.9b−f 268.6bcd 179.4cde 3.11a−d 2.88c−f 3.68a 3.15ab
G2 264.6a−e 166.3e−h 275.9abc 184.8bcd 3.27abc 2.64ef 3.38abc 3.00abc
G3 264.0a−e 176.2d−g 233.5c−g 142.7de 2.92cd 3.07b−e 3.45abc 2.77b−f
G4 279.5abc 203.5a−d 278.1abc 208.7abc 3.09a−d 3.15b−d 3.36a−d 2.98abc
G8 212.2def 127.3ı 209.0fg 165.8cde 3.19abc 2.56f 3.00def 2.76b−f
G9 257.5b−e 197.7b−e 264.7bcd 178.6cde 3.36abc 2.93b−e 3.30b−e 2.29f
G11 274.7a−d 237.9a 322.0a 247.0a 3.39abc 3.86a 3.42abc 2.83a−e
G13 201.1efg 158.5f−ı 188.0g 146.9de 2.65d 2.64ef 2.90f 2.46def
G14 282.5abc 206.9a−d 261.7b−d 186.8bcd 3.32abc 3.24bcd 2.89f 2.42ef
G16 149.0g 137.5hı 187.4g 134.7e 3.09a−d 3.49ab 3.18b−f 2.53c−f
G22 269.0a−d 216.7abc 294.6ab 231.0ab 3.25abc 2.94b−e 3.30b−e 2.96a−d
G25 173.3fg 144.4ghı 218.1d−g 175.9cde 2.95bcd 2.73def 2.91f 2.81a−e
G26 187.5fg 174.1d−g 258.1b−f 180.2cde 2.98bcd 2.90c−f 3.22b−f 2.72b−f
G28 266.1a−d 184.2c−f 279.8abc 210.7abc 3.56a 3.18b−d 3.69a 3.30a
G30 281.5abc 236.2a 278.3abc 205.6abc 3.54a 3.26bcd 3.50ab 2.85a−e
G31 257.7b−e 223.0ab 242.1c−f 200.1abc 3.41abc 3.49ab 3.28b−e 2.96abc
G32 231.9c−f 194.8b−e 265.4bcd 199.1abc 3.42abc 3.38abc 3.09c−f 2.84a−e
G34 323.3a 226.0ab 281.1abc 209.7abc 3.48ab 3.07b−e 3.11c−f 2.82a−e
G40 305.6ab 205.3a−d 257.4b−f 197.6bc 3.29abc 3.24bcd 2.96ef 2.73b−f
G45 224.5c−f 170.7d−h 212.6efg 164.1cde 2.96bcd 3.09b−e 3.00def 2.94a−d
Mean 246.6 188.8 253.8 187.5 3.21 3.09 3.23 2.81
Lower-case letters indicates significantly different according to P < 0.05.
Table 7
Fruit length and fruit width under irrigation and drought conditions in 2017 and 2018.
Genotype Seed length (mm) Seed width (mm)
2017 2018 2017 2018
Irrigated Drought Irrigated Drought Irrigated Drought Irrigated Drought G1 20.28c−f 20.55a 21.94a 19.72ab 9.30h 8.83hıj 9.46c−g 8.41e
G2 21.07b−f 18.51bcd 20.57a−f 18.76a−d 10.72cde 8.77ıj 10.24a−f 8.45e
G3 23.57a 18.63a−d 20.85a−d 18.79a−d 10.10efg 8.45jk 8.72g 9.24b−e
G4 21.17b−e 17.38de 19.72c−h 18.94abc 10.91b−e 9.78e−h 10.82abc 10.04abc
G8 18.77fgh 15.33f 19.10e−j 16.04fg 8.93h 7.61k 8.94efg 8.22e
G9 21.01b−f 18.94a−d 19.71c−h 17.18c−f 10.64c−f 10.19def 10.66abc 9.76a−d
G11 22.13a−d 20.58a 21.44ab 20.04a 12.08ab 12.26a 11.41a 10.56a
G13 17.32h 16.24ef 18.29hj 15.83g 10.09efg 9.10h−j 9.72b−g 8.54de
G14 19.97d−g 17.85cde 18.53ghj 16.90d−g 10.72cde 10.56c−e 10.37a−e 9.23b−e
G16 17.98gh 14.60f 17.89j 16.01fg 8.96h 8.26jk 8.88fg 8.22e
G22 20.38b−f 19.50abc 20.69a−d 19.19ab 10.57def 10.65b−d 9.94b−g 9.86abc
G25 21.10b−f 20.38ab 21.09abc 19.52ab 9.13h 8.23jk 9.98a−g 8.60de
G26 19.29e−h 17.69cde 18.88f−j 17.97b−f 9.88efg 9.55f−ı 9.81b−g 9.32b−e
G28 19.23e−h 17.65cde 19.08e−j 16.60efg 10.53def 9.96efg 10.92ab 10.28ab
G30 20.63c−f 20.29ab 19.99b−g 18.29a−e 10.86cde 11.15bcd 10.10a−g 9.83abc
G31 23.53a 20.41ab 20.20b−f 18.53a−e 12.69a 11.44abc 10.40a−d 8.81cde
G32 20.99b−f 18.09cde 19.43d−j 17.19c−f 11.87abc 11.57ab 11.12ab 10.15ab
G34 23.00ab 20.31ab 20.43a−f 19.26ab 11.77a−d 10.79b−d 10.95ab 10.39ab
G40 22.36abc 20.22ab 20.04b−g 19.15abc 11.60a−d 10.38def 10.16a−g 9.77a−d
G45 20.48b−f 17.17de 19.37d−j 16.89d−g 9.42gh 8.70ıj 9.14d−g 8.61de
Mean 20.71 18.52 19.86 18.04 10.54 9.81 10.09 9.32
3.5. Principal component analysis
The two year-average values of the yield, fruit characteristics, and seed quality parameters obtained for the pumpkin genotypes were subjected to principal component analysis (PCA) (Table 10). In the principal component analysis, components were generated considering the Eigenvalues greater than or equal to 1.0 (Kamrani et al., 2018). Considering the Eigenvalues, it was observed that thefirst three com-ponents explained 72.51% of the total variance in the irrigated condi-tions and 76.24% of that in the drought condicondi-tions. In order to e ffec-tively utilize and for correct interpretation of the PCA, it is required that the ratio of thefirst two or three components must be greater than 25% of the total variation (Mohammadi and Prasanna, 2003). Therefore, the high variance values obtained from thefirst three components in the present study indicated that the yield and quality components obtained in the present study could be explained strongly by the PCA analysis in both irrigated and drought conditions.
In the irrigated conditions, the first component (PC1) explained 40.63% of the total variation and demonstrated a strong positive cor-relation with average fruit weight, 1000-seed weight, and seed width. The second component (PC2) accounted for 19.43% of the total var-iation, while the fruit size exhibited a negative correlation; a positive correlation was observed in fruit width. The third component (PC3) explained 12.45% of the total variation, and a positive correlation was obtained between yield and fruit number, while the plant height de-monstrated a negative correlation with the yield and fruit number.
Correlatively, in drought conditions, PC1 explained 40.61% of the total variation and demonstrated a strong positive correlation with 1000-seed weight and seed width. PC2 and PC3 explained 22.35% and 13.26% of the total variation, and a positive correlation was obtained
between seed yield and fruit number; a negative correlation was ob-served between seed yield and fruit length. In both cases, seed weight and seed width demonstrated a strong correlation in PC1, and it was revealed that these were the important parameters in the selection of drought-tolerant pumpkin genotypes.
When the correlation table was analyzed, it was observed that the 1000-seed weight had a positive relationship with seed width and seed length; therefore, 1000-seed weight was considered a prominent para-meter in terms of seed quality in pumpkin. On the other hand, high positive relationship between seed yield and fruit number appeared in the PC3 for irrigated plots, while the same was identified in PC2 for drought conditions. As depicted in the correlation table, fruit number was an important parameter for high yield in drought conditions, and therefore, it was determined as an essential component in the selection of drought-tolerant pumpkin genotypes in arid as well as semi-arid regions. In the basic component analyses performed with 20 pumpkin genotypes in irrigated conditions, the distribution of the genotypes associated with the components was generated (Fig. 3). G11, G22, G30, and G31 exhibited the highest values for fruit weight, 1000-seed weight, and seed width, as described in thefirst component.
G9, G34, G40, and G45 exhibited the smallest values for fruit length and the highest values for fruit width, as described by the second component. G8 and G9 were associated with the highest yield and fruit number, and the shortest plant height in the third component.
As depicted inFig. 4, in drought conditions, the highest 1000-seed weight and seed width were obtained in G11, G22, G30, and G31, as explained by thefirst component. The second component associated G9, G13, and G14 genotypes with higher yield and fruit number. As described by the third component, the shortest fruits were obtained in the G45 genotype.
Table 8
Correlation coefficients between seed yield and fruit and seed characteristics under the drought conditions.
SY NF MFW PH FL FW TSW ST SL SW SY 1.000 NF 0.715** 1.000 MFW −0.048 −0.163 1.000 PH 0.397 0.004 −0.040 1.000 FL 0.324 −0.041 0.602** 0.685** 1.000 FW −0.228 −0.377 −0.196 −0.076 −0.183 1.000 TSW 0.181 −0.253 0.231 0.717** 0.622** −0.088 1.000 ST −0.248 −0.488* 0.115 0.344 0.164 −0.019 0.598** 1.000 SL 0.126 −0.387 0.291 0.355 0.419 0.084 0.669** 0.374 1.000 SW 0.273 −0.085 0.157 0.795** 0.602** 0.030 0.909** 0.558* 0.467* 1.000 Seed yield (SY); Number of fruit (NF); Mean fruit weight (MFW); Plant height (PH); Fruit length (FL); Fruit width (FW); Thousand seed weight (TSW); Seed thickness (ST); Seed length (SL); Seed width (SW).
* Statistically significant according to P < 0.05. ** Statistically significant according to P < 0.01.
Table 9
Correlation coefficients between seed yield and fruit and seed characteristics under the irrigation conditions.
SY NF MFW PH FL FW TSW ST SL SW SY 1.000 NF 0.035 1.000 MFW 0.378 −0.506* 1.000 PH −0.031 0.080 −0.545* 1.000 FL 0.366 −0.429 0.542* 0.345 1.000 FW 0.164 0.240 −0.104 0.114 0.040 1.000 TSW 0.515* −0.308 0.064 0.481* 0.564** 0.159 1.000 ST 0.476* −0.397 0.340 0.093 0.351 0.192 0.658** 1.000 SL 0.388 −0.362 0.257 0.253 0.504* 0.161 0.591** 0.364 1.000 SW 0.499** −0.183 0.228 0.454* 0.655** 0.169 0.743** 0.480* 0.447* 1.000 Seed yield (SY); Number of fruit (NF); Mean fruit weight (MFW); Plant height (PH); Fruit length (FL); Fruit width (FW); Thousand seed weight (TSW); Seed thickness (ST); Seed length (SL); Seed width (SW).
* Statistically significant according to P < 0.05. ** Statistically significant according to P < 0.01.
On the basis of evaluation of the irrigated and drought conditions, it was observed that G11, G22, and G30 resulted in impressive seed quality, and were therefore considered the prominent cultivar candi-dates. While G9 and G28, which presented high fruit number and yield in the irrigated conditions, were the highly recommendable genotypes for the irrigated conditions, G9, G13, and G14 should be evaluated in arid and semi-arid regions for breeding efforts in future.
4. Conclusion
The results of the present study demonstrated that drought exerted different effects on different pumpkin genotypes, and caused 80%
decrease on an average in the yield in both the experimental years. The parameters of 1000-seed weight and seed width, which were observed to be highly correlated in PC1, were identified as important in the selection of superior genotypes in pumpkin under irrigated and drought conditions. In addition, it has been well documented that 1000-seed weight had a positive relationship with 1000-seed width and 1000-seed length, because of which, 1000-seed weight was recommended as the most important parameter in determining the seed quality in pumpkin. Moreover, a high positive relationship between fruit number and seed yield appeared in PC3 in the irrigated conditions, while the same re-lationship was determined in PC2 in the drought conditions. As de-picted in the correlation table, fruit number was important for high seed yield in the drought conditions, and was, therefore, a determinant parameter in the selection of cultivars in arid and semi-arid regions.
G1 and G2 hybrids were the highest yielding commercial cultivars in both irrigated and drought conditions. According to the PCA, G11, G22, and G30 inbred lines had superior seed quality compared to the commercial cultivars, due to which they were evaluated as the cultivar candidates with superior agricultural traits. It is obvious that the aforementioned genotypes would gain high market value due to their significant seed quality. On the other hand, the G9 inbred line was observed to be the superior genotype in terms of yield and fruit number in both irrigated and drought conditions and was, therefore, re-commended for evaluation in future breeding studies and inclusion in hybrid programs in order to develop drought-tolerant cultivars.
Acknowledgments
This work was supported by the project of "18401001" by S.Ü-BAP office and is part of Musa SEYMEN's doctoral thesis.
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Result of principal component analysis for seed yield and fruit and seed characteristics under irrigation and drought conditions.
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