Mean Performance of diverse tomato species
Eleven genotypes were studied for higher yield and quality parameters (Table 2) and the relationship of average fruit weight (g) and number of fruits per plant with yield per plant (kg) is displayed in Fig 1. The genotype EC 538408 (1.79 kg) produced the maximum yield per plant followed by WIR 13700 (1.75 kg). In addition to this, EC 538408 was identified for maximum pericarp thickness (3.25 mm), polar diameter (3.22 cm), equatorial diameter (3.86 cm), lycopene content (8.24 mg/100 g), beta carotene content (0.84 mg/100 g) and average fruit weight (18.53 g).
Genetic variations in tomato genotypes
The results on genotypic and phenotypic covariance, variability, relative differences (RD), heritability and genetic advance as a percent were unveiled in Table 3. The results manifested that the genotypic variance (σ2g) varied from 0.04 (beta-carotene) to 12156 (number of fruits per plant). In similar fashion, beta- carotene represents the least (0.05), whereas number of fruits per plant (12159.38) reported the highest phenotypic variance. Also, the phenotypic variance is a little higher than the respective genotypic variance for all the traits, hence the expression of these traits is affected by the environment. Further, the PCV and GCV were categorised as low (<10%), medium (10% to 20%) and high (>20%) as suggested by
Sivasubramanian and Madhava (1973).
Based on these criteria, our results indicate that both GCV and PCV were higher for almost all the traits except for number of nodes to first flowering (15.53, 16.75), total soluble solids (16.01, 16.45) and days to first picking (8.19, 8.65), which shows moderate to low genetic variability. The significance of genetic variability is the necessity of any breeding population, not only for selection, but also provides imperative facts about the selection of parents for utilization in hybridization
(Upadhyay et al., 2019). The high genetic variability might be helpful for effective selection for the improvement of the traits. Analogous results were also observed by
Khuntia et al., (2019), Sinha et al., (2020), Venkadeswaran et al., (2020) and
Golani et al., (2023).
The relative difference (RD) is an estimation of the ratio of GCV to PCV. The estimated RD values varied from 0.00% (number of fruits per plant) to 7.28% for number of node to first flowering indicating minimum relative difference. So, the variation exists amongst the traits is due to genetic effect, which has a better response for direct selection.
The heritability of the traits ranged between 86.06% (number of node to first flowering) to 99.98% (number of fruits per plant). Generally high heritability (h
2b ≥60%) was marked for all the traits under study and genetic advance as a % of mean (GA %) varied from 15.96 (days to first fruit picking) to 160.30% (average fruit weight). Genetic advance was high (GA≤20%) for all traits except days to first fruit picking which indicate (10% ≤GA≤ 20%) moderate genetic advance.
Rasheed et al., (2023) noted high genetic advance (%) coupled with higher h
2b % for yield per plant and the number of fruits per cluster.
Anyaoha et al., (2023) recorded high heritability along with high genetic advance (%) for carotene content.
Apparently, in this work, all the traits had high heritability along with high GA (%) except days to first fruit picking which had high heritability along side with moderate GA (%). Traits manifested high heritability with high GA (%) indicates prevalence of additive gene effect, thus direct selection is effective. Therefore, it is meaningful to favour traits with high GCV, PCV, heritability and genetic advance
(Sabri et al., 2020). The powerful selection can be attained when additive genes effects are stronger than the environmental effects
(Usman et al., 2014).
Correlation and path analysis
Association among twenty-two traits based on Pearson’s correlation analysis given in Fig 2. Non-significant correlation was found for days to first flowering, number node to first flower, days to fifty percent flowering, days to first fruiting, number of fruits/truss, plant height at 60 DAT, titratable acidity, ascorbic acid, lycopene content and final plant height along with yield. β-Carotene had significant weak and positive association with yield (r= 0.38; p≤0.05). Pericarp thickness (r=0.68; p≤0.001), days to first picking (r=0.45; p≤0.01), polar diameter (r=0.74; p≤0.001), equatorial diameter (0.68, p≤0.001) and number of locules (r=0.56; p≤0.01) had highly significant positive and moderate (0:25 ≤r <0:75) correlation with yield and average fruit weight (r= 0.86; p= ≤0.001) had highly significant positive and strong correlation with yield. The positive correlation between average fruit weight, pericarp thickness, days to first picking, polar diameter, equatorial diameter, number of locules with fruit yield may suggest that these traits share some common gene. Number of flowers per truss (r= -0.81; p=≤0.001) and number of fruits per plant (r= -0.92, p=≤0.001) had highly significant negative and strong (0:75 ≤r <1:00) relation with yield. Moreover, TSS had significant weak (0:0 ≤ r < 0:25) and negative association with yield (r= -0.36; p≤0.05). Lower number of flowers per truss and number of fruits per plant may increase fruit weight leads to enhance the yield of tomato.
Adebisi et al., (2004) confirmed that reflection of correlation values amongst the variables is crucial for the selection of superior genotypes. Therefore, emphasis given on selection of higher fruit weight, pericarp thickness, polar diameter, equatorial diameter, lower number of flowers per truss and lower number of fruits per plant during the selection could be helpful for genetic improvement of tomato. Our results are in the same tune of
Sharma et al., (2019), Arya et al., (2023), Meena et al., 2023 and
Reddy et al., (2023).
The path coefficient analyses (Table 4) give clear idea about the nature of association between the different traits for forming proficient selection approach. The results revealed that the number of flowers/truss, days to first picking, polar diameter and TSS had positive direct effect on yield. However, highest positive direct effect on yield was exhibited by polar diameter. It is stated above that the correlation between the polar diameter and yield is positive and statistically significant (r=0.74; p≤0.01). This implies that higher polar diameter leads to increased fruit yield. Hence, selection based on polar diameter would be effective. Number of fruits per plant showed negative direct effect on fruit yield per plant (-1.92) similar to its correlation with yield (-0.92), implying that true relation exists between these traits. However, number of fruits per plant has high indirect effect on yield per plant through polar diameter (1.47). In the same way, number of locules, pericarp thickness and average fruit weight had positive indirect effect on yield through number of flowers per truss. Moreover, highest significant association between number of fruits per plant and yield (r= -0.92; p≤0.001) were observed, that may be due to the indirect effect of number of fruits per plant on polar fruit diameter. Thus, we advocated that selection based on polar diameter is made deliberately. Similar observations were also reported by
Sehgal et al., (2018), Ritonga et al., (2018) and
Sharma et al., (2019).
Cluster analysis
The dendrogram for cluster analysis is displayed in Table 5 and Fig 3 using “Star Software”. Cluster analysis help in selection of genotype based on nature and degree of genetic divergence. The result revealed that the genotypes were grouped into 3 major clusters. Cluster II comprised the highest proportion of genotypes (45.46%), including
Solanum chilense, EC 520076, EC 520060,
Solanum peruvianum and
Solanum cheesmanii. In contrast, Cluster III contained the lowest proportion (18.18%) with genotypes NTH 1831 and Akshaya, while Cluster I accounted for 36.36% of the total population, consisting of four genotypes
viz., EC 538408, WIR 13700, EC 520075 and
Solanum pimpinellifolium.
The genotype chosen from different cluster for hybridisation may results in isolation of transgressive segregants. The random distribution of genotypes of different origin in a single cluster designated that the diversity might be due to genetic architecture, heterogeneity or homogeneity of traits and history of selection. Different clustering patterns confirmed by
Sinha et al., (2021), Vargas et al., (2020) and
Naveen et al., (2018).
Principal component analysis (PCA)
It is used to short the traits based on contribution to the total variation at each axis of differentiation. In the current research, PCA divide their 100% diversity into ten components in which four principal components
i.e., PC1 (8.10), PC2 (7.38), PC3 (2.77) and PC4 (1.59) had more than 1 eigen value with 90.18% of cumulative variability (Table 6 and Fig 4). The PCs with less than 1 eigen value were considered non-significant and display lesser variability between the genotypes. Thus, it is inferred that data correspond to the first four PCs had higher variability. Therefore, the selection from these PCs will be valuable.
Iqbal et al., (2014) reported 3 PCs with more than 1 eigen-value
The factor loading of traits is represented in Table 7 and Fig 5A revealed that the PC1 allowed maximum loading of traits like days to first flower, days to fifty percent flowering, days to first fruiting, days to fifty percent fruiting and TSS. In PC2, average fruit weight and no. of fruits/plant, in PC3, ascorbic acid and β-carotene and in PC4, lycopene and number node to first flower showed maximum positive loading. By considering these traits it showed that these PCs regulate the total variation for all yield contributing traits. Positive factor loading indicated significant variation in yield and quality trait so it plays important role for selection on the basis of yield and quality of tomato.
Sehgal et al., (2018) and
Sinha et al., (2021) observed that number fruits per plant, lycopene, ascorbic acid, titratable acidity contributed positively to PC.
Kumar et al., (2017) reported that average fruit weight, TSS and fruit yield per plant give positive contribution to PC. Thus, trait-based selection might be helpful to formulate a valuable selection approach for further tomato improvement programs.
The biplot diagram (Fig 5B) shows the association among the traits and between genotype × traits. The vector length gives a picture of the contribution of traits to total variance, the longer the vector length, the higher the contribution of those traits. The trait yield/plant, polar diameter, pericarp thickness and average fruit weight showed the highest vector length representing its involvement to the entire diversity. The genotypes close to the vector trait are probably the best performing for particular traits. The genotype EC 538408 performs better for the polar diameter, yield/plant, pericarp thickness and average fruit weight; however NTH 1831 associated with days to first flower, days to fifty percent flowering and days to first fruiting.