INTRODUCTION Cucumber (Cucumis sativus L.) is a popular vegetable grown in both open and protected environmental conditions around the world. Cucumber is indigenous to northwest India and it has been grown for at least three thousand years. Its juice is frequently advised as a source of silicon for skin health. Cucumber is high in vitamins A, B, B5, C, and K, as well as minerals such as magnesium, potassium, copper, phosphorus, and manganese. Cucumbers having caffeic acid and ascorbic acid aid to minimize skin irritation and swelling. India has a tropical and subtropical climate, the predominance of high temperatures throughout the year makes it difficult to get better yields and excellent quality vegetables in open environmental conditions. Protected farming is a distinct and specialized type of agriculture in which the microclimate surrounding the plant is partially or completely regulated according to the needs of the plant species farmed (Mishra et al., 2010). The protected cultivation of cucumbers could be used to improve their vegetative growth, yield, quantity and quality (Singh et al., 2012; Ganesan, 2002). Seed crops produced in open fields particularly in Kharif, are heavily plagued with cucumber mosaic virus and some other insect pests, for which no reliable management technique is currently available. Furthermore, changing climatic conditions, increased temperature and an increase in the incidence of insect pests and diseases drastically reduce seed yield and quality in the Kharif crop, and the relatively early onset of high temperature hampers the production of female flowers, fruit set, and fruit development in the Kharif crop. Due to its flexibility and high output under plastic house conditions, most farmers started growing hybrid cucumbers inaccessible regions during the off-season to earn remunerative returns. Even in naturally ventilated poly homes, yields are higher than in open fields (Srivastav and Singh, 1997; Gautam et al., 2008). Insect pest problems in protected farming are considerably different from pest problems in open fields (Rani and Reddy et al., 1999) (Reddy and Kumar et al., 2006). Less light intensity gives rise to more female flowers whereas more light intensity causes more male flowers Growing seed crops in protected structures, such as poly houses, can help to relieve these issues by shielding the crop from various insect vectors and poor environmental conditions. As a result, the current study was designed to investigate growth behaviour, flowering and fruit development parameters in cucumbers during kharif under Tamil Nadu conditions. MATERIALS AND METHODS The present investigation was conducted at the western farm of the Department of Vegetable Science, Horticultural College and Research Institute (HC&RI), TNAU, Periyakulam in 2022 to evaluate the 5 varieties i.e., Heera, Japanese Long Green, K-75, Konkan Kakadi, Pant Khira-1, collected from various institutions/universities of Indian Council of Agricultural Research cultivated by TNAU recommended agronomical practices equipped with fertigation system. The spacing of 110 cm × 60 cm was maintained in raised beds with a single row system under polyhouse and open conditions. For both conditions, three replications were adopted for each variety in a Factorial Randomized Block Design (FRBD) with 2 factors (Growing conditions and Varieties). Based on soil and leaf studies, chemical fertilizers were applied. Soluble fertilizers were injected into irrigation water or sprayed on the leaves of plants to supplement micronutrient deficits (except for Iron which is used in the irrigation system). Ammonium sulphate, potassium sulphate (low solubility), superphosphate triple (poor solubility), magnesium sulphate, manganese sulphate, zinc sulphate, and Fe chelate were among the fertilizers used. Naturally Ventilated Poly House (NVPH). The saw-toothed structured poly house had various facilities like a double door, exhausted fan and cooling pad system, fogging system, shade net, and fertigation system. Open environmental condition. In open conditions without any environmental control system but same agronomic practices followed, such as dimensions of the plot, date of sowing, training, fertigation, and intercultural operations. RESULTS AND DISCUSSION Tables 1 and 2 show the data on the performance of various cucumber varieties in two different habitats in terms of plant development characteristics, flowering, and fruit characters under the naturally ventilated poly house as well as in open field conditions. The statistical analysis showed substantial variations between the growth conditions and different varieties. Vegetative growth parameters. Vegetative growth characteristics such as vine length at 30 DAS, vine length at 60 DAS, and number of nodes per vine were recorded for different varieties of cucumber under open and protected conditions. From Table 1, it was concluded that significantly maximum vine length at 30 DAS (31.88 cm), vine length at 60 DAS (216.14 cm) and number of nodes per vine (28.24) were recorded under protected conditions and minimum recorded under open field conditions. This might be attributed to increased photosynthesis and respiration as a result of the protected house beneficial microclimate. This is consistent with the findings of Kumarand Arumugam (2010) and Priya et al. (2002) on vegetables produced in poly houses, as well as Ryelski (1985) and El-Aidy et al. (1989) on sweet pepper cultivated in shade net houses. In between varieties, Japanese Long Green showed maximum vine length at 60 DAS (207.50 cm), a number of nodes per vine (37.45), followed by Heera (267.80 cm, 28.22 cm) respectively. The vine length at 30 DAS was significantly maximum recorded in the Heera variety (28.98 cm) on par with Japanese Long Green (27.68 cm), whereas among the interactions Japanese long green under protected conditions showed maximum vine length at 30 DAS (46.55 cm), vine length at 60 DAS (44.13 cm), number of nodes per vine was recorded in Japanese Long Green under open field conditions (37.45). The outcome of these characters was in accordance with Chaudhari et al. (2016); Dahal et al. (2020). Reproductive parameters. Table 2 revealed the significantly maximum nodal position of the first male and female flower recorded under open conditions (8.11, 10.78) respectively, and the early nodal stage of the male (6.00) and female flower (8.58) shown under protected conditions. The results conform with Singh et al. (2004). In varieties, early nodal position of male (3.35) and female flowers (5.25) was noticed in the Heera hybrid. Among the interactions, the early (3.19) nodal position of the first male flower was recorded in Japanese Long Green under protected conditions and the early (4.31) female flower nodal position was recorded in Heera under protected conditions and late nodal position of male (10.45) and female flower (13.2) seen in Pant Khira-1 under open conditions. The differences in the first emergence of female flower could have been due to internodal length, number of internodes, genetic nature, environmental factors and vigour of the crop. Rawat et al. (2014); Patel et al. (2013) reported such variations among various cucumber cultivars for the nodal position of first pistillate flower and staminate flowers. Days to first picking. Days to first picking significantly maximum (57.89 days) was recorded under open field conditions over the protected conditions (49.05 days), this might be owing to a build-up of photosynthates, which stimulated the early commencement of flowers. Rui et al. (1989) discovered similar results in capsicum. Heera hybrid took minimum (43.86 days) days for first picking and the maximum days taken for first picking in Konkan Kakadi (62.17 days) variety. In interactions, Japanese Long Green variety under protected conditions took less (38.12) days for first picking and more (65.79) days took in Konkan Kakadi under open field conditions. Similar findings were reported by Kumar et al. (2013); Kumar et al. (2019). Days to the last picking. Fig. 1 shows that protected conditions (91.92 days) took maximum days for last harvest compared to the open field conditions (88.01 days), whereas varieties K-75 (93.7 days) had the maximum days for last picking and minimum days taken in Heera hybrid (82.86 days). In individual interactions, maximum days were shown in Japanese Long Green under protected grown conditions (94.22 days), and minimum days were reported in Heera hybrid under open field conditions (80.45 days) for days to last picking. The present findings are in agreement with those reported by Cardoso and Silva (2003); Afangideh and Uyoh (2007). Fruit length (cm). Fig. 1 shows that Protected conditions (19.34 cm) obtained maximum fruit length and minimum fruit length was noted under open field conditions (18.03 cm), and Japanese Long Green (25.04 cm) had longest fruit and minimum fruit length recorded in the K-75 variety (15.88 cm). Among all the interactions, Japanese Long Green under protected (26.94 cm) obtained the longest fruit and the shortes fruit was noted in K-75 under open field conditions (15.67 cm). The difference in fruit length could have been due to the genetic nature of the variety, environmental factors, and vigour of the crop. Similar findings are reported by Hossain et al. (2010); Yadav et al. (2012); Patel et al. (2013); Kaddi et al. (2014). Yield per plant (kg/plant). Fig. 2 shows that protected conditions (3.02 kg) obtained maximum yield and open conditions (1.45 kg) was noticed as the lowest yield, among all the varieties Heera hybrid (3.13 kg) had the maximum yield, followed by the Japanese Long Green (2.98 kg/ha) and minimum yield was noticed under Konkan Kakadi (1.31 kg/ha). In individual interactions, maximum yield was noted in the Heera hybrid under protected conditions (4.25 kg/ha) and the lowest yield was noticed in Konkan Kakadi under open field conditions (0.9 kg/ha). These findings back up previous research of Afangideh and Uyoh (2007); Soleimani et al. (2009).