Squash (Cucurbita pepo L.), a polymorphic member of the Cucurbitaceae family, is widely cultivated as a summer vegetable under tropical and subtropical climates (Dunsin et al., 2019; Gülşen et al., 2022; Tartoura et al., 2014). Turkey, ranking eighth globally, produces squash both in open fields and under low tunnels, with greenhouse cultivation concentrated in the Mediterranean and Aegean regions (Nacar, 2022). With a short growth cycle (45-60 days), squash is primarily grown in spring and summer, though high summer temperatures often reduce yield and affect fruit color (Massolo et al., 2019). Valued for its low calorie content, high fiber and nutritional benefits, summer squash also holds medicinal potential (Nada and Metwaly, 2020). Global production reached 24.2 million tons in 2023, led by China, India and Ukraine (FAO, 2025). Turkey’s production rose from 547,208 tons in 2020 to 615,000 tons in 2023 (TUIK, 2025). Exports also grew steadily, with Mersin serving as a major hub for markets such as Russia and the Middle East (Anonymous, 2022).  Sustainable agricultural practices are increasingly vital in the face of climate change, resource depletion and environmental pressures. In vegetable production, balancing productivity with ecological responsibility is essential for long-term sustainability (Jamil et al., 2021). Research highlights that aligning cultivar selection and planting time with local agroclimatic conditions significantly boosts yield and stress tolerance (Bannayan et al., 2011; Khanum et al., 2021). According to the World Bank (n.d.), climate projections indicate a 2-3/^oC temperature rise in Mersin by 2040 and up to 4/^oC by 2070, suggesting that autumn may become a more suitable season for squash cultivation. Therefore, evaluating hybrids and standard cultivars across different seasons in terms of yield and fruit quality is increasingly important.
       
The integration of agricultural products into global markets is a key aspect of sustainability. For major producers like Turkey, maintaining stable quality and yield in export crops is essential for trade continuity. Extending the growing season of exportable vegetables such as squash can strengthen supply chain sustainability.
       
Mersin stands out in Turkey for both squash cultivation and export. While production mainly occurs in spring, summer and autumn cultivation is also feasible (Okasha et al., 2020). As a warm-season crop, squash can be grown year-round if harvested immaturely (Abou El-Salehein et al., 2019). Despite its wide cultivation in Turkey, research on seasonal performance is limited.
               
Expanding squash production into autumn may support export sustainability in Mersin. This study compares spring and autumn cultivation periods for hybrid and standard cultivars, focusing on yield and fruit quality. Expanding squash production into autumn may support export sustainability in Mersin. This study compares spring and autumn cultivation periods for hybrid and standard cultivars, focusing on yield and fruit quality.

Experiment location
 
This study was conducted in Tarsus, located on the eastern Mediterranean coast of Turkey (36^o49'20.8"N, 34^o53'9.1"E; 5/ m a.s.l.), during the spring and autumn of 2022. The region has a typical Mediterranean climate with hot, dry summers and mild, wet winters. Based on 30-year data, the annual average temperature is 20-21^oC, with summer temperatures often exceeding 30^oC and winter temperatures rarely falling below 10^oC (MGM, 2022). Annual precipitation is 600-700mm, mostly occurring in winter and spring. Fig 2 shows variations in temperature and weather conditions, providing environmental context for the study.
       
Mersin’s low elevation and coastal location provide high humidity year-round, supporting an extended growing season for warm-season vegetables. Rising regional temperatures may enhance year-round production capacity (Bağçaci ​et al., 2021). Spring offers favorable conditions with higher temperatures and lower rainfall. Increasing autumn temperatures due to climate change may also allow for second-crop cultivation. Climate data for spring and autumn 2022 were obtained from the Turkish State Meteorological Service (MGM) and are shown in Fig 3.
       
The soil at the experimental site was slightly alkaline (pH 8.01) and non-saline (EC 0.547 dS/m), with high lime content (31.91%) and low organic matter (1.07%), indicating a need for fertility improvement. Potassium was adequate (110.31 kg/da), while phosphorus was excessive (22.5 kg/da) (Table 1). Although suitable for vegetable cultivation, the soil was amended in autumn or early spring with 2-4 tonsda of well-decomposed farmyard manure and 25-50 kg/da of elemental sulfur.


       
This study used 10 squash cultivars: 5 F1 hybrids (Alba F1, Amelthee F1, Hadra F1, Hürrem F1, Vildan F1) and 5 standard types (Pelin, Black pumpkin elite, Nazlı, White bush, Eskenderany). Seedlings were planted in spring and autumn using a randomized plot design (Acar, 2020), with three replications of 10 plants each (30 plants per cultivar). Plant spacing was 50 cm within rows and 80 cm between rows. The trial was conducted on 150 m² flat land with 8 kg/da of base fertilizer (20.20.0), drip irrigation and black nylon mulch (Kumar and Sharma, 2018; Farah et al., 2021). Emitters were spaced 30 cm apart (2 L/h) and irrigation was applied when 25% of available water was depleted. No topdressing was used. Spring planting occurred on April 10 with harvest starting May 15; autumn planting was on September 1 with harvest beginning October 10, both over four weekly harvests. Yield was evaluated by fruit weight, length, diameter, fruit number per plant and yield per plant. Quality was assessed by flesh firmness, soluble solids, fresh and dry weight. Dry weight was measured after oven-drying fruits at 65/ °C to constant weight.
       
Yield measurements; fruit weight (g) was determined by weighing 5 randomly selected fruits per replicate using a digital scale (Seles Nhb 600 g, 0.01 g precision). Fruit length and diameter (mm) were measured with a digital caliper (0.01 mm accuracy). Harvests were carried out weekly for four weeks before rind hardening. Fruit number per plant was calculated by dividing the total fruit count by the number of plants per replicate and yield per plant (g/plant) was calculated by dividing total fruit weight by plant number. Data from three replications were averaged for statistical analysis and observations covered all growth and harvest stages.
       
Fruit quality; flesh firmness (FFH, kg/cm²) was measured on 5 randomly selected fruits per replicate using a hand penetrometer with an 8 mm tip. Water-soluble dry matter (WSDM, %) was determined with an Atago PAL-1 refractometer using a drop of juice from the same samples. Fresh (FFW) and dry fruit weight (FDW) were measured with a precision scale (Seles Nhb 600 g, 0.01 g) and fruits were oven-dried at 65^oC to constant weight. FDW was recorded in grams following Kaçar (1972). All measurements were performed on 10 fruits per replicate.
 
Data evaluation
 
Data were analyzed using SPSS 23 (IBM, 2022). Two-way ANOVA assessed the effects of season, cultivar and their interaction on yield and fruit quality. Data were checked for normality and variance homogeneity before analysis. Mean comparisons used Duncan’s Multiple Range Test at p≤0.05  (Duncan, 1955). Results are shown as means, with statistical differences indicated by different letters.

Yield related measurements
 
Yield analysis showed that season, cultivar and their interaction significantly affected average fruit weight, length, diameter and fruit number per plant (Duncan’s test, p≤ 0.05). Among varieties, the standard cultivar ‘Pelin’ had the highest average fruit weight (294.82 g), longest fruit length (208.59 mm) and most fruits per plant (13.22). ‘Eskenderany’ showed the largest fruit diameter (58.15 mm). These results indicate superior morphological traits in standard cultivars ‘Pelin’ and ‘Eskenderany’. The season × cultivar interaction revealed the best yield traits in spring: ‘Hadra F1’ produced the heaviest fruits (368.84 g), ‘Pelin’ the longest (213.77 mm), ‘Eskenderany’ the widest (64.25 mm) and ‘Vildan F1’ the highest fruit number per plant (21.84) (Table 2).


       
Squash, a warm-climate crop, performs best under high light and moderate moisture (Dunsin et al., 2019; Tartoura et al., 2014; Massolo et al., 2019). Climate data showed spring had 0.1^oC higher temperatures and 16.06 mm less precipitation than autumn. Increased autumn rainfall likely reduced sunlight, negatively affecting flowering and fruit set (Bannayan et al., 2011). Fig 1-3 support that autumn’s lower temperature and light availability led to reduced yields. Mersin’s low elevation, coastal location and high humidity in spring created optimal conditions for early vigorous growth and higher yields.






       
Khanum et al., (2021) also reported that planting time significantly affects productivity and morphological traits like fruit weight, length, diameter and yield. In this study, average fruit weight ranged from 137.66 to 368.84 g, generally higher than the 54.35 to 229.6 g reported by Kuslu et al., (2014) and El-Gazzar et al. (2020). Fruit length ranged from 144.10 to 213.77 mm (14.41-21.38 cm), exceeding the 8.3 to 18.47 cm noted by Dunsin et al., (2019) and Shehata and Abdelgavad (2019). Fruit diameter (42.43-64.25 mm) was comparable to or slightly above the 13.9 to 56.7 mm reported by Hassan et al., (2016) and Shehata and Abdelgavad (2019). The number of fruits per plant (6.56-21.84) was substantially higher than the 6.08-11.02 and 6.00-7.60 ranges reported by El-Shoura (2020) and Shafeek et al., (2016), respectively.
 
Yield
 
Squash yield was significantly affected (p≤0.05) by season, cultivar and their interaction. The highest yield occurred in spring, averaging 2595.12 g/plant. Among cultivars, ‘Vildan F1’ had the highest mean yield at 3062.18 g/plant (Table 3).       


       
Season × cultivar interaction showed consistently higher yields in spring than autumn. ‘Vildan F1’ had the highest yield in both seasons, with 4939.37 g/plant in spring and 1185 g/plant in autumn. Other high performers in spring were ‘Hürrem F1’ (3513.75 g/plant) and ‘Hadra F1’ (3423.33 g/plant), indicating better hybrid response to spring conditions. Yield reduction in autumn is likely due to climatic factors such as less solar radiation and increased rainfall, which negatively affect pollination and fruit set. The consistently high yield of ‘Vildan F1’ across both seasons indicates its lower sensitivity to environmental fluctuations, suggesting its genetic stability. This highlights the importance of multi-environment analysis tools such as AMMI and GGE biplot in identifying stable genotypes (Muniswamy et al., 2022); (Dolhey and Kandalkar, 2023).
       
Singh et al., (2020) reported pumpkin yields of 425 kg/100 m² in open fields. Similarly, Yeboah et al., (2020) and Khanum et al., (2021) highlighted the strong seasonal impact on squash productivity, with lower autumn yields. Bannayan et al., (2011) emphasized temperature’s key role in summer squash growth, especially during pollination.
       
In this study, autumn rainfall was 16.06 mm higher than spring, likely reducing sunlight and shortening the photoperiod. This decrease in light may have hindered female flower formation and fruit set, lowering yields. These results align with previous findings that optimal temperature and solar radiation are critical for maximizing squash yield.
 
Fruit quality
 
The results showed that fruit flesh hardness (FFH), water-soluble dry matter (WSDM), fresh fruit weight (FFW) and fruit dry weight (FDW) were significantly affected (p≤0.05) by season, cultivar and their interaction. Spring had the highest values for all except WSDM, which was higher in autumn, consistent with reports that dry matter increases late in the season due to physiological accumulation (Rosales et al., 2023; Stoyanova et al., 2018). Higher autumn dry matter is linked to lower temperatures and shorter days promoting assimilate buildup.
       
‘Vildan F1’ and ‘Hürrem F1’ had the highest FFH (9.98 and 9.94 kg/cm²). The highest WSDM (3.96%) was found in ‘Amelthee F1’, ‘Hürrem F1’ and ‘Black Squash Elite’ during autumn. ‘Pelin’ had the highest fresh fruit weight (294.82 g), while ‘Vildan F1’ had the highest dry weight (17.24 g) in spring. The cultivar × season interaction showed ‘Hadra F1’ had the highest FFH (10.50 kg/cm²) and fresh weight (368.84 g) in spring. These findings highlight the importance of both genotype and season on squash fruit quality (Table 4).


       
Fruit quality deterioration often involves loss of firmness and wilting, linked to changes in tissue water potential  (Rodríguez-Burgos et al., 2015). Ozdüven (2016) reported squash fruit flesh hardness between 8.00 and 8.14 kg/cm² under limited water, influenced by irrigation and planting time, with higher firmness under hot, dry and well-lit conditions. This aligns with our finding of greater firmness in spring, when temperature and light were more favorable, supporting the impact of photothermal conditions on firmness and dry matter accumulation. Both Ozdüven (2016) and Okasha et al., (2020) noted that water-soluble dry matter (WSDM) is affected by season and plant water status, consistent with higher WSDM in autumn squash due to cooler temperatures and slower growth.  ‘Hadra F1’ (10.50 kg/cm²) and ‘Hürrem F1’ (10.33 kg/cm²) showed superior flesh firmness; ‘Pelin’ had the highest fresh fruit weight (340.49 g) and ‘Vildan F1’ the highest dry weight (17.24 g). These results align with Dunsin et al., (2019), who reported fresh weights of 248.5-488 g and dry weights of 9.13-16.97 g, confirming the reliability of our data and highlighting genotype × environment interactions in fruit quality. Spring’s higher temperatures, lower rainfall and increased solar radiation created favorable photothermal conditions improving firmness and fresh weight. Cooler, more humid autumn conditions slowed growth, increasing dry matter accumulation. Thus, seasonal variations in quality reflect environmental influences.

This study shows that spring cultivation of summer squash (Cucurbita pepo L.) in Mersin’s Mediterranean region yields significantly better results than autumn. Average spring yield (2595.12 g/plant) was about four times higher than autumn (635.51 g/plant), mainly due to favorable climate higher temperatures, 16.06 mm less precipitation and more solar radiation. These conditions improve photoperiod and light interception, supporting growth, flowering and fruit set. ‘Vildan F1’ was the most productive cultivar in both seasons, with 4939.37 g/plant in spring and 1185 g/plant in autumn. ‘Hürrem F1’ and ‘Hadra F1’ also performed well in spring, highlighting strong genotype × environment interactions.
       
Spring-grown fruits had higher flesh hardness and fresh/dry weight, while autumn fruits had higher water-soluble dry matter (WSDM), likely due to cooler temperatures slowing growth and increasing dry matter accumulation. ‘Hadra F1’ and ‘Hürrem F1’ showed the highest firmness in spring; ‘Amelthee F1’, ‘Hürrem F1’ and ‘Black Squash Elite’ had highest WSDM in autumn. Climate projections suggest rising autumn temperatures may improve autumn squash cultivation prospects.
       
Given Mersin’s role in squash export, extending production into autumn could enhance sustainability and supply continuity. However, optimizing planting time, cultivar choice and soil management especially addressing high lime (31.91%) and low organic matter (1.07%) is essential for consistent autumn yields. Integrating seasonal climate and crop data emphasizes the need to align production with environmental conditions to maximize yield, quality and long-term sustainability amid climate change.

This study was prepared based on some data from Mehmet Can Özmen’s master’s thesis titled “Evaluation of the production and quality characteristics of summer squash (Cucurbita Pepo L.) varieties in Mersin”.

All authors declared that there is no conflict of interest.