Variability and Character Association in F 2 Segregating Population of Different Commercial Hybrids of Tomato ( Solanum lycopersicum L.)

: The F 2 segregating generations of exotic tomato hybrids were studied to measure variability, character association and path coefficient analysis. Analysis of variance for each trait showed significant differences among the genotypes. Very little differences were observed between phenotypic coefficients of variation (PCV) and genotypic coefficients of variation (GCV) for the traits days to first flowering (pcv=9.21, gcv=7.82), fruit length (pcv=17.14, gcv=14.84) and fruit diameter (pcv=17.10, gcv=14.92). High heritability (>50%) was observed for all the yield contributing characters except flowers per cluster (47.83%). High heritability associated with high genetic advance was observed for fruit clusters per plant (105.11), fruits per plant (103.43), branches per plant (34.49), fruits per cluster (47.43), individual fruit weight (77.73) and fruit yield per plant (108.25). Selection for such traits might be effective for the fruit yield improvement of tomato. Significant positive genotypic and phenotypic correlation was observed between plant height at first flowering, flowers per plant, fruits per cluster, fruit clusters per plant, fruits per plant with fruit yield per plant. Fruits per plant showed the highest positive direct effect (1.096) on fruit yield per plant followed by individual fruits per plant (0.674). Direct selection may be executed considering these traits as the main selection criteria to reduce indirect effect of the other characters during the development of high yielding tomato variety. @ JASEM Tomato

Tomato is one of the most important and popular winter vegetable in Bangladesh. Tomato is an introduced crop in Bangladesh and provides less genetic variability. It is estimated that the genomes of tomato cultivars contain <5% of the genetic variation of their wild relatives. Since the 20 th century, human beings have created a huge array of morphologically different cultivars and forms from the single species S. lycopersicum via plant breeding. Through domestication, research and breeding activities that were implemented by scientists and breeders worldwide, modern tomato varieties (mostly hybrids) have been developed with all shapes, colors and sizes (Bai and Lindhot, 2007). In Bangladesh most of the tomato varieties are of inbred type, those are low yielder. Average yield of tomato is very low (7.51 t/ha) in Bangladesh compared to other tropical countries (15.1 t/ha in India) in the world (Annon., 2004). Very recently exotic hybrid varieties are being introduced due to their high yield potentiality. Seed costs of those hybrid varieties are very high. Moreover, due to unique nature of hybrid variety, the tomato growers need to buy seeds every year. The local cultivars of tomato are more or less susceptible to Fusarium sp., Ralstonia solanacearum, Leaf Curl Virus and Leaf Yellowing Virus. Due to infestation of these pathogens singly or simultaneously, yield decreases in some degrees (Opena et al., 1990).
In the past, very little efforts have been taken for development of inbred lines of tomato through the exploitation of genetic variability present in the exotic hybrids. F 2 generation obtained from the selfing of F 1 hybrid provides all possible variations. So selection with particular objectives in F 2 generation is very much effective and selfing of those selected genotypes generation after generation helps to develop inbred lines (similar to the parental lines of the exotic hybrids). These inbreds with desired characters including high yield potential can be used as High Yielding Variety (HYV) as well as the parents for hybrid variety. To increase the genetic yield potential, the maximum utilization of the desirable characters for synthesizing of any ideal genotypes is essential. Variability in tomato is expected to be immense as the fruits vary greatly in shape and size (Dixit and Dubey, 1985;Bhardwaj and Sharma, 2005). Studies on genetic parameters and character associations provide to select and help to develop optimum breeding procedure. Many researchers (Kamruzzahan et al., 2000) have reported different genetic parameters in tomato based on few traits. As yield is the main object of a breeder, it is important to know the relationship between various characters that have direct and indirect effect on yield. The degree of relationship or association of these characters with yield can be ascertained by correlation studies. This would aid in formulating an efficient breeding program for improving the yield potential via its components (Frageria and Kokli, 1997). Considering all the facts described above the present investigation was undertaken with the following objectives: (1) To estimate genetic variability in the first segregating generation obtained from the exotic hybrids, (2) To develop inbred lines with high yield potential and tolerant to wilts and viruses AND (3) To study the character association.

MATERIALS AND METHODS
The experiment was conducted at the experimental field, Department of Genetics and Plant Breeding, Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Salna, Gazipur during the winter season (September'07 to March'08) on an upland soil. The location of the site is the center of Madhupur Tract (24 0 05′ N latitude and 90 0 25′ E longitudes) characterized by more or less rainfall free during October to February and heavy rainfall during the month from May to September with an elevation of 8.4 meter from the sea level. The soils of BSMRAU farm belongs to Salna series of Shallow Red-Brown Terrace soil type (Brammer, 1971;Shaheed, 1984) with silty clay in surface and silty clay loam in sub-surface region. The soil was silty clay loam with pH 6.5, CEC 25.58 and C:N ratio 10:3. Seeds of first segregating generation of 40 exotic tomato hybrids were used as experimental materials. Supreme Seed Company (Bangladesh) Ltd tested field performance of 40 hybrid varieties of tomato collected from exotic sources. F 2 seeds of each hybrid were collected from that trial. The hybrids were Abhiruchi-1, Abhiruchi-3, Abhiruchi-4, Abhiruchi-6, Abhiruchi-9, Abhiruchi-10, Udayan Plus, Udayan, Unnayan, Aradhana, New Improve Aditi, Winall-01, Winall-06, Sonali, IHT, PS-058, WHT-03, WHT-04, PS-052, PS-053, PS-059, PS-060, Epoch, Mintoo, Deepam, TyKing-5, Bankim-206, Supera, Noven, Indian-531, Nidhi, TyQueen, Akash, TH-10, Disha, Jamuna, Alpona, Ruchi, TyRex, Hanyest Grace-02.  Burton (1952). Broad sense heritability was estimated (defined by Lush, 1949) by the formula, suggested by Hanson et al. (1956) and Johnson et al. (1955). The expected genetic advance for different characters under selection was estimated using the formula suggested by Lush (1949) and Johnson et al. (1955). For calculating the genotypic and phenotypic correlation coefficient for all possible combination the formula suggested by Johnson et al. (1955) and Hanson et al. (1956) were adopted. Correlation coefficient were further partitioned into components of direct and indirect effects by path coefficient analysis originally developed by Wright (1921) and later described by Dewey and Lu (1959).

RESULTS AND DISCUSSION
The estimates of range, mean, genotypic (σ 2 g ) and phenotypic (σ 2 p ) variance, genotypic (GCV) and phenotypic (PCV) coefficients of variation, heritability (h 2 b ) and genetic advance (GA) as percentage of mean for 12 characters are presented in Table 1. The range of variation was much pronounced in most of the characters. The phenotypic variance and phenotypic coefficient of variation were higher than genotypic variance and genotypic coefficient of variation, respectively for most of the yield contributing characters studied except days to first flowering, fruit length and fruit diameter. The results indicated that most of the yield attributes were under the influence of environment. High heritability (>50%) was observed for all the yield contributing characters except flowers per cluster. The high heritability coupled with high genetic advance in percent mean was observed for fruit clusters per plant, fruits per plant, branches per plant, fruits per cluster, individual fruit weight and yield per plant suggested that effective selection may be done for these characters. Similar results have also been reported by Haydar et al. (2007), Mariame et al. (2003), Singh et al. (2002), Bharti et al. (2002), Pradeepkumar et al. (2001), Prasad and Rai (1999), Phookan et al. (1998), Padmini and Vadivel (1997), Singh et al. (1997), Pujari et al. (1995), Mishra and Mishra (1995).  Agong et al. (2008), Haydar et al. (2007), Mohanty (2003), Harer et al. (2003), Mohanty (2002a), Mohanty (2002b) in tomato.
Path Coefficient Analysis: Fruits per plant showed the highest positive direct effect (1.096) on fruit yield per plant (Table 2) showing high direct effect on yield per plant indicated that direct selection for these traits might be effective and there is a possibility of improving yield per plant through selection based on these characters. Residual effect was 0.231, which was contributed by characters not used in path analysis. Similar results have also been reported by Dhankar et al. (2001), Verma and Sarnaik (2000), Mageswari et al. (1999), Prasad and Rai (1999), Yadav and Singh (1998), Singh et al. (1997) and Linda and Scott, 1992.  Residual effect: 0.231, ** and * -significant at 1% and 5% level of probability, respectively.