Introduction

Tomato (Solanum lycopersicum L.; 2n = 2x= 24) is one of the most consumed vegetable in the worldwide and better plant genetic analysis system. It's considered as a nutritional powerhouse compared with other vegetable crops (Chattopadhyay et al., 2013). Agro-statistics include India as second highest tomato producers in the world after China. In 2013, the growing area reached 88 thousands hectare, resulting in a total production of about 18.22 million tons (share about 11.15% of the world tomato production). In India, an average yield of tomato (20.71 t/ha) is lower than the world average (34.85 t/ha) (FAO, 2013). There is demand for development of high yielding varieties and or hybrid cultivars of tomato to increase the productivity per unit area. Hybrids are usually known to be characterized by good quality characters and high yield (gives 3 to 4 times more yield in contrast to that of open pollinated variety). Therefore, tomato hybrid cultivars were, extensively, used in commercial production (Solieman et al., 2013). However, yield is a complex character and its direct improvement is difficult (Meena et al., 2015). Heterosis breeding provides an efficient means to break the yield barrier in most of crops including tomato. Heterosis in tomato was first observed by Hedrick and Booth (1968) for higher yield and more number of fruits per plant. Since then, heterosis for yield and its related traits were widely studied by several researchers (Amin et al., 2001; Bhatt et al., 2001; Kurian et al., 2001; Bai and Lindhout, 2007; Garg et al., 2013; Shalaby, 2013; Solieman et al., 2013; Kumar et al., 2015). Heterosis manifestation in tomato is in the form of the greater vigour, faster growth and development, earliness in maturity, increased productivity, higher levels of resistance to biotic and abiotic stresses (Yordanov, 1983). It is an important tool that can facilitate yield enhancement from 30% to 400% and help enrich many other desirable quantitative and qualitative traits in crops. Keeping these facts in view, the present investigation was planned and executed with the objective to estimate the extent of heterosis among the crosses, obtained from eleven diverse lines and four testers, crossed in line×tester pattern.

 

1 Result and Discussion

Analysis of variance for experimental design (Table 1) revealed that variance due to replications was very low in magnitude and differences were significant for most of the characters studied except plant height, average fruit weight, number of fruits per plant, harvesting span, pericarp thickness and number of locules per fruit. This showed that the experimental plot was heterogeneous in fertility level. Highly significant differences among genotypes were present for all the characters studied. The percent heterosis over better parent and standard check for different traits are presented in Table 2.

 

 

1.1 Performance of traits related to earliness

Of forty four hybrids, twelve hybrids exhibited significantly negative heterosis ranged from -32.93% (Sel 12-1-16×PVB-2) to -16.89% (7-4×58-18-1-1) over the respective better parent and thirty hybrids recorded significant heterosis over the standard check NS-524 ranged from -49.45% (7-4×55-26-1-1) to -14.69% (PVB-1×55-26-1-1) for days to 50% flowering. Cross combinations viz. 7-4×55-26-1-1, Sel 12-1-17×115-1-8-1, Sel 12-1-16×PVB-2, 102-8-6-1×58-18-1-1, 102-8-6-1×PVB-2, 7-5-1×PVB-2, 7-4×58-18-1-1, 2-1×PVB-2, 102-8-5-1 × PVB-2, 102-8-5-1×115-1-8-1, 7-4×PVB-2 and PVB-1×PVB-2 showed significant and negative heterosis over better parent and the standard check NS 524. Early flowering leads to earliness and also early supply of the produce in the market and enables it to fetch a remunerative price. Thus, heterosis for days to first flowering had been estimated in terms of earliness. Baisiiya et al. (2001) reported negative heterosis over better parent ranging from 15.28%, (EC-44881×EC-130204) to -5.36% (EC-429×Pant T-1) for that trait. Negative heterosis for days to 50% flowering has also been reported by Singh et al. (2012).

 

An early flowering is not always a vital criterion for determining earliness, as some hybrids which exhibited early flowering could not show earliness in harvest. Therefore, days taken to first harvest are equally important in determining the earliness of the hybrids. In case of days to first harvest, the negative heterosis was ranged from -6.49 (CH-2-2×115-1-8-1) to -21.98 % (102-8-5-1×PVB-2) over better parent and -7.81 (102-8-5-1×55-26-1-1) to -29.69 % (102-8-5-1×58-18-1-1) over check hybrid NS-524. Joshi and Thakur (2004) and Negi et al. (2012) also reported significant negative heterosis for days to first harvest in tomato.

 

Six cross combinations viz. Sel 12-1-16×55-26-1-1 (10.98 and 76.78%), Sel 12-1-17×55-26-1-1 (9.6 and 54.83%), CH-2-2×55-26-1-1 (24.67 and 25.67%), 102-8-6-1×58-18-1-1 (24.54 and 20.65%), CH-2-2×58-18-1-1 (22.83 and 23.81%) and 102-1-6-1×55-26-1-1 (17.11 and 12.89%) showed positive and significant heterosis over both better parent and check hybrid NS-524, respectively for plant height. Similar result was also reported by Premalakshme et al. (2005) and Sharma and Thakur (2008).

 

 

1.3 Performance of fruit and yield traits

In case of average fruit weight, only six cross combinations exhibited significant and positive heterosis over both better parent and check, whereas, twenty eight hybrids show over the respective check only. Cross combinations namely CH-2-2×55-126-1-1 (22.35 and 89.71%),  CH-2-3-1×55-26-1-1 (10.53 and 66.44%), Sel 12-1-16×58-18-1-1 (14.17 and 59.21%), 102-8-6-1×PVB-2 (7.3 and 54.79%), Sel 12-1-16×55-26-1-1 (8.7 and 51.56%) and 102-8-6-1×58-18-1-1 (19.43 and 43.09%) showed significant and positive heterosis over both better parent and check hybrid NS-524, respectively. It indicated that the high percentage of heterosis over the better parent was derived from the hybrids involving parents with high average fruit weight because fruit weight directly influenced the total yield per plant. Negi et al. (2012) observed the cross combination PS×CH (51.92%) and PSH×PU (46.88%) had maximum heterosis over better parent in desirable positive direction.

 

 

Five cross combinations viz. 2-1×55-26-1-1 (105.89 and 65.35%), 2-1×PVB-2 (104.43 and 59.09%), Sel 12-1-16×55-26-1-1 (68.46 and 73.62%), PVB-1×55-26-1-1 (36.00 and 61.93%) and 7-4×PVB-2 (19.70 and 70.95%) exhibiting  positive significant heterosis over better parent and check NS-524, respectively for number of fruits per plant. Most of the workers have inferred that hybrids had positive heterosis for number of fruits per plant in tomato (Thakur et al., 2004; Singh et al., 2005; Rani and Veeraragavathatham, 2008). Solieman et al. (2013) reported heterosis ranged from 4.37 to 104.69% for number of fruits per plant over mid parent value.

 

Total fruit yield per plant is one of the most important traits, which deserve highest consideration in any breeding programme. With relevance to total yield, the crosses revealed a significant and positive heterosis over better parent ranged from 19.56 (102-1-6-1×55-26-1-1) to 103.07 per cent (CH-2-2×55-26-1-1) and heterosis over standard check ranged from 26.43 (102-1-6-1×55-26-1-1) to 130.71 per cent (CH×115-1-8-1). Nine cross combinations, namely CH-2-2×55-26-1-1 (103.07 and 114.42%), CH-2-2×115-1-8-1 (77.43 and 130.71%), CH-2-2×58-18-1-1 (70.58 and 38.41%), Sel 12-1-16×55-26-1-1 (68.46 and 73.62%), 2-1×PVB-2 (41.79 and 50.45%), PVB-1×55-26-1-1 (36.00 and 61.93%), Sel 12-1-16×115-1-8-1 (32.32 and 72.17%), 102-1-6-1×58-18-1-1 (21.34 and 29.39%) and 102-1-6-1 × 55-26-1-1 (19.56 and 26.43%) showed positive and significant heterosis over both better parent and check hybrid NS-524, respectively. In cross combination EC-4881×EC-130204 (1l3.03%) showed highest heterosis over better parent, reported by Baisiiya et al. (2001). Solieman et al. (2013) reported heterosis ranged from 22.29 to 64.33% for total fruits yield per plant. Kumar et al. (2015) observed heterosis ranged from 4.98 to 55.25% and 4.55 to 47.17 % over the better parent and standard check respectively. Heterosis for fruit yield was also reported by Thakur et al. (2004); Premalakshme et al. (2005); Harer et al. (2006) and Sharma and Thakur (2008).

 

Longer harvest span directly enhances the production. Out of forty four hybrids, seven hybrids over better parent and none of the hybrids over standard check NS-524 reported significant and desirable positive heterotic effects. The positive heterosis over better parent was ranged from 8.30 (PVB-1×115-1-8-1) to 13.45 per cent (102-1-6-1×58-18-1-1). Thakur et al. (2004) and Sharma and Thakur (2008) also observed positive heterosis for harvesting span. Three cross combinations namely, Sel 12-1-17×PVB-2 (15.73%), 102-1-6-1×PVB-2 (14.28%) and 7-4×PVB-2 (5.41%) reported heterosis for fruit shape index over better parent, whereas, six cross combinations viz. 2-1×115-1-8-1 (22.45%), 7-5-1×115-1-8-1 (20.07%), 7-4×PVB-2 (19.39%), 7-5-1×55-26-1-1 (16.33%), 7-5-1×58-18-1-1 (10.54%) and 7-5-1×PVB-2 (8.50%) showed positive significant heterosis over check.

 

Thicker pericarp is considered desirable for distant transportation. Nine hybrids recorded significant positive heterosis ranging from 17.64 (CH-2-3-1×58-18-1-1) to 29.98 per cent (Sel 12-1-17×115-1-8-1) over the better parent. When compared to the standard check, six hybrids showed significantly positive heterosis ranged from 10.22 (Sel 12-1-17×55-26-1-1) to 12.98% (PVB-1×55-26-1-1). The cross combinations namely, Sel 12-1-17×55-26-1-1 (23.18 and 10.39%) and PVB-1×55-26-1-1 (19.17 and 12.99%) exhibited significant and positive heterosis over better parent and check hybrid NS-524, respectively. Solieman et al. (2013) reported heterosis ranged from -9.22 to 25.88% for pericarp thickness. Kumar et al. (2015) observed heterosis range from -50.59 to 70.79% and from -43.65 to 45.49% over the better parent and standard check respectively for this character. Gaikwad and Cheema (2009) also reported positive heterosis for pericarp thickness.

 

Number of locules in a fruit is the indicator of the fruit firmness. Lesser the number of the locules per fruit more is the fruit firmness and vice versa. The cross combination 2-1×115-1-8-1 recorded minimum number of locules per fruit and it showed -33.33 and -35.06% heterosis over the better parent and standard check, respectively. The hybrid viz. 2-1×PVB-2 (-37.56%) showed highly negative significant heterosis over better parent followed by 2-1×115-1-8-1 (-33.33%), 7-4×PVB-2 (-32.19%), 7-5-1×55-26-1-1 (-31.05%), 2-1×55-26-1-1 (-28.26) and so on. While the cross combinations 2-1×115-1-8-1 and 7-4×58-18-1-1 showed highest negative significant heterosis over check hybrids NS-524 followed by 7-5-1×55-26-1-1(-27.92%), 2-1×55-26-1-1 (-25.11%), 7-5-1×115-1-8-1 (-20.67%) and so on. Solieman et al. (2013) observed heterosis ranged from −35.72 to 49.02% for number of locules per fruit. Kumar et al. (2015) reported heterosis ranged from -50.59 to 70.79% and from -43.65 to 45.49% over the better parent and check respectively to this trait. Significant negative heterosis for number of locules per fruit had also been reported by Abd allah and Gad El-Hak (2000); Singh et al. (2005) and Gaikwad and Cheema (2009).

 

1.4 Performance of quality traits

For processing purpose, TSS content should be > 4.5%. With increase in 1% of solids resulted in 20% increase in recovery of processed product of tomato (Kumar et al., 2015). With relevance to TSS, thirteen hybrids expressed significant positive heterosis over better parent ranged from 8.53 (2-1×55-26-1-1) to 19.77% (Sel 12-1-16×115-1-8-1), whereas, when compared to the standard check NS-524, nine hybrids showed positive significant heterosis ranged from 7.56 (102-8-5-1×55-26-1-1) to 24.42% (Sel 12-1-16×115-1-8-1). Solieman et al. (2013) reported heterosis range of -11.46 to 25.50% for TSS. Cheema et al. (2014) observed the most heterotic hybrid (Acc.No.3×Acc.No.5) showed a 51.52% increase over better parent and 21.07% over the check.

 

High lycopene content imparts deep red colour to the tomato, which is preferred for table as well as processing purpose. Moreover, lycopene had greatest antioxidant property among all carotenoids (Rai et al., 2004) and is valued for its anti-cancer property, since it acts as a scavenger of free radicals. Eight hybrids recorded significant positive heterosis over better parent ranging from 10.62 (Sel 12-1-17×55-26-1-1) to 58.19% (102-1-6-1×55-26-1-1), while twenty hybrids exhibited significant heterosis over check ranged from 19.46 (102-8-6-1×PVB-2) to 152.83% (Sel 12-1-16×115-1-8-1). Gaikwad and Cheema (2009) reported 145.57 and 131.57% increase in lycopene content over the standard checks Punjab Upma and TH-1, respectively.

 

2 Conclusion

PFrom the above study, it was concluded that the hybrid Sel 12-1-16×115-1-8-1 which was superior over check for days to 50% flowering, days to first harvest, average fruit weight, plant height, total fruit yield, TSS, and lycopene content, and it was superior over better parent for total fruit yield, TSS, and lycopene content. Similarly, 2-1×PVB-2 was found superiority over both better parent and check NS-524 for days to 50% flowering, days to first harvest, number of fruits per plant, total fruit yield, and lycopene content. PVB-1×55-26-1-1 showed superior over check NS-524 for almost all characters studied except harvesting span, number of locules per fruit, TSS and lycopene content. Thus, these hybrids have the potential to be exploited commercially.

 

3 Materials and Methods

3.1 Experimental materials

The study involved forty four F^₁ hybrids were made in a line x tester fashion by using eleven lines (PVB-1; Sel 12-1-16; Sel 12-1-17; CH-2-2; CH-2-3-1; 2-1; 102-1-6-1; 102-8-5-1; 102-8-6-1; 7-4; 7-5-1) with four testers (115-1-8-1; 58-18-1-1; 55-26-1-1; PVB-2); and a check NS 524 (commercially grown hybrid from Namdhari Seeds Private Limited, India). The present investigation was carried out at Vegetable Research Farm, Department of Vegetable Science, Punjab Agricultural University, Ludhiana, India during 2010-11, which is situated at 30°54 North latitude, 70°45 East longitude and at a mean altitude of 247 m above sea level. The experimental materials were sown in nursery beds on 24th July, 2010 and their seedlings were transplanted in the field (at a spacing of 120×30 cm) on 30th August, 2010 for the evaluation of trail. Before sowing, seeds were treated with Captan @ 2-3 g/kg of seed.

 

3.2 Experimental design and data recorded

The experimental design was a randomized complete block design with three replications. In each replication, there were ten plants in a row for each entry. Each row was 4 m long and 1.2 m wide. Cultural practices, such as fertilization, irrigation, and weeds, diseases and insect-pests control were performed whenever they were thought necessary, as per the package of practices for cultivation of vegetables recommendations of the Punjab Agricultural University (Anonymous, 2010).

 

Observations were based on five central plants in a row leaving one plant on each side of the row per replication for each genotype on twelve quantitative and qualitative characters viz., plant height (cm); days to 50% flowering; days to first harvest; average fruit weight (g); number of fruits/plant; total fruit yield (kg/plant); harvesting span (days); fruit shape index; pericarp thickness (cm); number of locules per fruit; TSS (%); lycopene content (mg/100 g of fresh weight).

 

3.3 Statistical analysis

The magnitude of heterosis was estimated in relation to better parent as well as standard check, NS 524. Both were calculated as percentage increase or decrease of F^₁s over the better parent (BP) and standard check (SC) values.

Percent heterosis over better parent = (F^₁-BP)/BP×100

Percent heterosis over check = (F^₁-SC)/SC×100

where, BP and SC = performance of the better parent and standard check, respectively.

 

Authors' contributions

SKJ conceived of the study, participated in its design and drafts the manuscript. AK carried out genetic studies and performed the statistical analysis.

 

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