The analysis of variance indicated highly significant differences among the genotypes for all the characters studied, which has revealed the existence of sufficient variability in the germplasm (Table 3). Fruit length ranged from 14.01 cm to 31.48 cm with a mean of 20.92 cm. Similar results for fruit length variations are reported by Valcarcel et al., (2018) with a range of 12.5 cm to 35.6 cm. The fruit diameter recorded at the middle portion of the fruit showed variations ranging from 3.25 cm to 6.87 cm. Jat et al. (2014) reported similar results for fruit diameter (4.16 to 6.82 cm). Significant variations were observed for individual fruit weight among genotypes and it ranged from 130.33 g − 334 g. Kumar et al. (2020) have reported similar results in cucumber accessions (124.63 g − 417.55 g). The stalk length of the fruit ranged from 1.08 cm to 4.48 cm. Zhang et al. (2012) reported similar results in the cucumber accessions for fruit stalk length (1.3–6.1 cm). The fruit flesh thickness was the most important fruit quality traits in cucumber and the results showed significant variations among genotypes studied, it ranged from 0.84–1.92 cm. Shet et al. (2018) found similar results for fruit flesh thickness (0.50–3.00 cm) in the germplasm evaluated by them. Seed cavity breadth was in the range of 1.63 cm − 3.93 cm. Higher the seed cavity breadth, lower was the fruit flesh thickness. The seed cavity length showed significant differences among the genotypes and it ranged from 13.42 cm to 23.62 cm. Ranjan et al. (2015) reported similar results for seed cavity breadth (2.35 cm to 4.42 cm) and seed cavity length (3.15-7.0 cm) in cucumber genotypes. Total Soluble Solids (TSS) showed significant differences among the genotypes (0.93 to 2.05 ºBrix). Similar variations in TSS from 3.98–5.38 ºBrix has been reported by Jat et al. (2014). The shelf-life of the fruit increased with decrease in physiological loss in weight (PLW) and it was 3.25 days − 5.5 days in the present study. Ranjan et al. (2015) observed similar variations in shelf-life (2.1-7.0 days). The individual fruit weight was recorded at physiological maturity, and the physiological maturity was judged based on a fruit turning green to yellow or brown depending on the local genotype. The fruit weight ranged from 358.36 g to 880 g, similar results for fruit weight variation at physiological maturity (326 g − 567 g) has been observed by Ranjan et al. (2019). Number of fruits per plant showed significant variations with a range of 5.25–11.25. Similar results for number of fruits per plant (1.33–5.80) are reported by Pandey et al., (2018). The total yield per plant (1.12 kg − 3.05 kg) varied significantly among 22 cucumber genotypes. Rajawat et al. (2017) reported similar variations in total fruit yield per plant in cucumber genotypes with a range of 1.13–2.31 kg.
The genetic variability is the key factor for selection of superior genotypes in breeding programmes. The higher variations contribute to efficient selection. The PCV for all the traits was higher than GCV (Table 4). Fruit diameter, fruit weight, fruit stalk length, fruit flesh thickness, seed cavity breadth, TSS, fruit weight at physiological maturity, number of fruits per plant and yield per plant have high (20%) GCV and PCV. The traits such as fruit length, seed cavity length and shelf-life have exhibited medium (10–20%) GCV and PCV. Heritability of all the traits (fruit length, fruit diameter, fruit weight, fruit stalk length, fruit flesh thickness, seed cavity breadth, seed cavity length, TSS, shelf-life, fruit weight at physiological maturity, number of fruits per plant and yield per plant) were high (60%). Genetic advance as percent mean was high (20%) for fruit length, fruit diameter, fruit weight, fruit stalk length, fruit flesh thickness, seed cavity breadth, seed cavity length, TSS, fruit weight at physiological maturity, number of fruits per plant and yield per plant. Only shelf-life had moderate (18.56%) GAM. High heritability coupled with high GAM was observed for all the traits except shelf-life, which possessed high heritability coupled with moderate GAM. Karthick et al. (2019), Shet et al. (2019) and Sidhu (2012) have reported similar estimates of genetic variability in cucumber genotypes.
Table 4
Estimates of genetic variability for fruit and yield related traits in twenty-two local cucumber genotypes
Traits | Mean | Range | PCV (%) | GCV (%) | h2 (%) | GAM (%) |
Min | Max |
FL (cm) | 20.92 | 14.01 | 31.48 | 15.82 | 15.59 | 97.13 | 31.65 |
FD (cm) | 4.84 | 3.25 | 6.87 | 24.28 | 23.95 | 97.34 | 48.68 |
FW (g) | 218.79 | 109.00 | 334.00 | 36.12 | 35.09 | 94.41 | 70.24 |
FSL (cm) | 2.44 | 1.08 | 4.48 | 31.64 | 30.82 | 94.86 | 61.83 |
FFT (cm) | 1.18 | 0.84 | 1.92 | 23.59 | 21.72 | 84.74 | 41.18 |
SCB (cm) | 2.66 | 1.63 | 3.93 | 25.93 | 25.00 | 92.97 | 49.67 |
SCL (cm) | 16.56 | 13.42 | 23.62 | 15.23 | 14.45 | 89.93 | 28.22 |
TSS (ºBrix) | 1.16 | 0.93 | 2.05 | 27.27 | 25.01 | 84.12 | 47.26 |
SL (days) | 4.36 | 3.25 | 5.5 | 14.86 | 11.57 | 60.26 | 18.56 |
FWPM (g) | 501.81 | 358.36 | 880.00 | 31.23 | 29.80 | 91.04 | 58.57 |
NFPP | 8.66 | 5.25 | 11.25 | 22.76 | 21.44 | 88.74 | 41.60 |
YPP (kg) | 1.97 | 1.12 | 3.05 | 31.63 | 30.60 | 93.56 | 60.96 |
(Index: FL-fruit length, FD- fruit diameter, FW-fruit weight, FSL-fruit stalk length, FFT-fruit flesh thickness, SCB-seed cavity breadth, SCL-seed cavity length, TSS, SL-shelf-life, FWPM-fruit weight at physiological maturity, NFPP-number of fruits per plant and YPP-yield per plant) |
The correlation coefficient for twelve traits was analyzed among twenty-two local cucumber genotypes to understand the association between the traits (Table 5). The traits such as fruit weight (0.948), fruit flesh thickness (0.873), seed cavity breadth (0.924) and yield per plant (0.749) were positively correlated with fruit weight and fruit diameter. Further, the fruit flesh thickness was positively correlated with seed cavity breadth (0.693) and yield per plant ( 0.612) and the fruit shelf life was also positively corelated with fruit weight at physiological maturity (0.639). The yield per plant was majorly correlated with fruit weight (0.844), fruit diameter (0.749), fruit flesh thickness (0.612) and seed cavity breadth (0.769). Hence, selection of the genotypes for these traits would lead to the higher production. Sharma et al. (2018) also reported similar results with significant positive correlation between yield per plot and number of fruits per plant (0.773, 0.850). Lakshmi and Reddy (2020) observed that, the fruit yield per plant was having significantly positive correlation with number of fruits per plant, fruit length, fruit diameter, fruit weight and TSS.
Table 5
Correlation coefficient between fruit and yield traits among local cucumber genotypes
Traits | FL (cm) | FD (cm) | FW (g) | FSL (cm) | FFT (cm) | SCB (cm) | SCL (cm) | TSS (ºBrix) | SL (days | FWPM (g) | NFPP | YPP (kg) |
FL (cm) | 1 | | | | | | | | | | | |
FD (cm) | -0.392 | 1 | | | | | | | | | | |
FW (g) | -0.243 | 0.948* | 1 | | | | | | | | | |
FSL (cm) | 0.322 | -0.611* | -0.598** | 1 | | | | | | | | |
FFT (cm) | -0.335 | 0.873* | 0.817** | -0.618* | 1 | | | | | | | |
SCB (cm) | -0.292 | 0.924* | 0.898** | -0.440** | 0.693* | 1 | | | | | | |
SCL (cm) | 0.724* | -0.177 | -0.071 | 0.125 | -0.026 | -0.123 | 1 | | | | | |
TSS (ºBrix) | -0.064 | 0.429** | 0.380 | -0.147 | 0.466** | 0.450** | 0.086 | 1 | | | | |
SL (days | -0.063 | -0.144 | -0.123 | 0.363 | -0.208 | -0.196 | -0.393 | -0.071 | 1 | | | |
FWPM (g) | 0.498** | -0.093 | 0.032 | -0.071 | -0.127 | -0.105 | 0.169 | -0.224 | 0.409 | 1 | | |
NFPP | 0.660* | -0.600* | -0.505** | 0.639* | -0.589* | -0.476** | 0.256 | 0.038 | 0.403 | 0.400 | 1 | |
YPP (kg) | 0.077 | 0.749* | 0.844* | -0.345 | 0.612* | 0.769* | -0.022 | 0.493** | 0.123 | 0.263 | -0.030 | 1 |
The marker assay
The SSR markers linked to fruit flesh thickness gene- Csa2M058670.1 with a four base pair mutation in thin flesh genotypes, were screened for the polymorphism. Thirteen SSR primers (Table 6) exhibited 0.25 to 0.37 PIC values with a mean of 0.35. The markers SSR 23420 and SSR 10849 showed moderate PIC value (0.37), which was on par with Valcarcel et al. (2018) reports on SSR markers, with PIC values ranging from 0.04 to 0.49 with mean of 0.29. Normohamadi et al. (2017) also reported the PIC of 0.44 to 0.8. The major allele frequency ranged from 0.55 to 0.82 with a mean of 0.64. The higher major allele frequency was observed in SSR 20248 (0.82) and the minimum was found in SSR 10849 (0.55). Kumar et al. (2020) reported the major allele frequency between 0.36 (UW084186) to 0.97 (UW084478) with a mean value of 0.70. The higher gene diversity was observed in SSR 23420 and SSR 10849 (0.50) and lower gene diversity was recorded in SSR 20248 (0.30) with a mean of 0.46. Pandey et al. (2017) found similar results with gene diversity (0.074–0.428) and Lv et al. (2012) also reported gene diversity of 0.30–0.74.
Table 6
List of candidate gene (fruit flesh thickness) markers showing major allele frequency, gene diversity and PIC
Marker | Major allele frequency | Gene diversity | PIC |
SSR00204 | 0.64 | 0.46 | 0.36 |
SSR00289 | 0.64 | 0.46 | 0.36 |
SSR18937 | 0.64 | 0.46 | 0.36 |
SSR13532 | 0.64 | 0.46 | 0.36 |
SSR03593 | 0.64 | 0.46 | 0.36 |
SSR23832 | 0.64 | 0.46 | 0.36 |
SSR22558 | 0.64 | 0.46 | 0.36 |
SSR23420 | 0.55 | 0.50 | 0.37 |
SSR01374 | 0.64 | 0.46 | 0.36 |
SSR10849 | 0.55 | 0.50 | 0.37 |
SSR20248 | 0.82 | 0.30 | 0.25 |
SSR00378 | 0.64 | 0.46 | 0.36 |
SSR00030 | 0.64 | 0.46 | 0.36 |
Mean | 0.64 | 0.46 | 0.35 |
Dendrogram analysis based on molecular data obtained from SSR markers grouped twenty-two local cucumber genotypes into two clusters viz., cluster-I and cluster II in the dendrogram ( Fig. 1.). Cluster I composed of 8 genotypes and cluster-II with 14 genotypes. Further cluster-I was divided into two sub-clusters, cluster-IA and cluster-IB. Cluster-IA included four genotypes (DGLM, DGM, VLD and KPL) and all exhibited fruit flesh thickness of 0.84–0.94 cm and cluster-IB included another four genotypes (MUCHANDA, CSGLD, HVR, CSJ-1) with fruit flesh thickness measured 0.85–0.99 cm. Similarly, cluster-II was divided into two sub-clusters, cluster-IIA and cluster-IIB. The cluster IIA grouped all the genotypes collected from three locations viz., Hassan, Channarayapattanna and Golithadaka (CSLG, CSLW, CSSL, CSHLH, CSHLC-1, CSWL, NATTI, CSG-3, CSHL-1, CSG-2, CGLB and CSG-1), all the fruits exhibited white peel and bigger core, with brown peel upon maturity. Whereas, the cluster-IIB contained only two genotypes viz., CSHLA and CSHLC-2 from same ecological regions viz., Arakalagudu and Holenarasipur. All the genotypes in cluster II exhibited very close phenotypic traits, indicating common geographic origin and spread to local nearby regions, as these local types are cultivated even till date for commercial purpose, with some special features such as longer fruit length, uniform shape and size, white peel with crispy and tasty thick fruit flesh.