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ISSN : 1225-8504(Print)
ISSN : 2287-8165(Online)
Journal of the Korean Society of International Agriculture Vol.35 No.3 pp.139-147
DOI : https://doi.org/10.12719/KSIA.2023.35.3.139

Genetic Variability and Traits Relationship Studies of WorldVeg Tomato Genotypes in Nepal

Binod Prasad Luitel*,**, Dipendra Ghimire*, Surendra Lal Shrestha*, Hyo Bong Jeong***, Eun Young Yang****, Myeong Cheoul Cho**†
*National Horticulture Research Centre, Nepal Agricultural Research Council, Khumaltar, Lalitpur, 5459, Nepal
**Allium Vegetable Research Institute, National Institute of Horticultural and Herbal Science, Rural Development Administration,
Muan, 58545, Korea
***Vegetable Research Division, National Institute of Horticultural and Herbal Science, Rural Development Administration,
Wanju, 55365, Korea
****Department of Horticulture, Korea National College of Agriculture and Fisheries, Jeonju, 54874, Korea
† Corresponding author (Phone) +82-10-9906-5326 (E-mail) chomc@korea.kr
February 20, 2023 September 6, 2023 September 6, 2023

Abstract


This study was conducted to assess the genetic variability and correlation of phenotypic characteristics in 12 tomato (Solanum lycopersicum L.) genotypes including 11 WorldVeg and one commercial variety (Pusa Ruby) in Terai (plain) region of Nepal in 2021–2022. This experiment was laid out in a randomized complete block design with three replications. The phenotypic traits, including days to 50% flowering, plant vigor and height, fruit number/plant, fruit yield, fruit weight and diameter, fruit firmness and fruit pericarp thickness, and total soluble solids (TSS) content of the fruits, were studied. Analysis of variance revealed significant differences among the genotypes for all the traits except for plant vigor. The genotype of AVTO1705 resulted the highest fruit yield (2.9 kg/plant) than Pusa Ruby, a commercial check (0.5 kg/plant). The phenotypic coefficient of variation (PCV) was higher than the genotypic coefficient of variation (GCV) for all the traits and PCV values were maximum for the number of fruits, fruit yield, and fruit weight. High PCV, GCV, and genetic advance (GA) were observed for yield, fruit weight, and plant height, respectively, indicating the additive gene effect. High heritability for fruit yield/plant and plant height inferred the phenotypic selection for their genetic improvement. Fruit yield was significantly (P<0.05) positively correlated with the fruit number and fruit weight, and direct selection of these traits are reliable for yield improvement in tomato.


Correlation , Genetic variability , Genetic advance , Heritability , Selection

네팔에서 세계채소연구소에서 육성된 토마토 우량 계통의 유전적 변이와 형질 상관에 관한 연구

Binod Prasad Luitel*,**, Dipendra Ghimire*, Surendra Lal Shrestha*, 정효봉***, 양은영****, 조명철**†
*네팔농업연구회 국립원예연구소
**농촌진흥청 국립원예특작과학원 파속채소연구소
***농촌진흥청 국립원예특작과학원 채소과
****국립한국농수산대학교 원예학부

초록

    INTRODUCTION

    Tomato (Solanum lycopersicum L.) is the second most important vegetable crop after potato in the world (FAO, 2021). This is an annual crop and belongs to Solanaceae family. It is being used worldwide due to its high nutritional values (Dorais et al., 2008). In Nepal, tomato is the third most important vegetable crop after cauliflower and cabbage, covering 22,600 ha with a total production of 432,646 MT, and productivity of 19.14 MT/ha (MoALD, 2021). It is cultivated during spring and summer season at mid hills, winter season at terai, and summer season at high hills. But normal tomato production (June-August) in the high hills is considered off-season in the mid-hills of Nepal (Maharjan, 2019).

    Tomato cultivation is a source of income generation for Nepalese farmers in Terai region. Currently, four open-pollinated and three hybrid cultivars are registered from public sector, but more than 24 hybrids varieties are registered by private sectors through Seed Quality Control Centre, Nepal (CPDD, 2021). Registered hybrid cultivars are mostly imported from abroad and the origin of cultivars is unknown. Imported hybrid seeds are expensive which increases the cost of production to farmers. Moreover, most of the varieties recommended so far are for culinary purposes, and only few of them are used for processing particularly for ketchup industry. Due to the change of food habit of consumers, the demand for table tomatoes has been increasing in Nepal in recent years. Present varieties have not addressed the consumers’ changing interests. The productivity of tomato in Nepal is lower than India (25.0 MT/ha) and China (48.0 MT/ha) (FAOSTAT, 2018). Hence, introduction of high yielding new tomato genotypes is important for the selection and development of new cultivars.

    Genetic improvement of a crop depends on the presence of genetic variability in the population. The genetic variation of tomato is necessary for improving its quality and yield characters (Hassan et al., 2021). PCV, GCV, heritability and GA are important tools to detect the genetic variability in a population (Islam et al., 2012). The ratio of genotypic variance to the phenotypic variance is referred as heritability, which represents the heritable part of the variation (Singh, 2001). Heritability alone cannot present a reliable character for the response to selection and GA is the most powerful tool to predict the genetic gain under selection (Johnson et al., 1955). Heritability and genetic diversity are useful, and allowed plant breeders to design efficient breeding strategies for selection (Adhikari et al., 2018). Furthermore, various traits are associated with each other and linked to economic traits. Therefore, it is necessary to examine association among the traits affecting fruit yield that helps to identify the most important traits to be considered for the selection. Many researchers have studied the genetic parameters, correlation among the fruit and yield traits in tomato germplasms, and they have reported many recommendations to develop new cultivars with desirable traits (Islam et al., 2012;Ahirwar et al., 2013;Singh and Singh, 2018;Hassan et al., 2021). However, there are few researches on fruit and yield traits, and variability parameters specifically on WorldVeg tomato genotypes in Nepalese conditions. This study will provide the important information to breeders for selecting the traits in tomato breeding programs. Furthermore, selection of high yielding tomato genotypes will provide more varietal options to the farmers of Terai region. Thus, the aims of this study were to investigate some important fruit and yield traits, to evaluate the genetic variation based on the measured traits and to study the correlation between phenotypic traits of WorldVeg tomato genotypes grown in Terai region of Nepal.

    MATERIALS AND METHODS

    Experimental site and plant materials

    This research was conducted at the horticulture research farm of Directorate of Agricultural Research (DoAR), Khajura, located at latitude 28° 06" N and longitude 81° 37" E, 181 m above sea level, Lumbini Province, Nepal. This location represents western terai region of Nepal and the climate is characterized as tropical type. In this region, May and January are the warmest and coldest months, respectively. The average annual temperature in the research site is 23.7°C and it receives average 1,172 mm of rainfall annually. Rainfall mostly occurs from June to August and November–January are the dry seasons. The soil texture was sandy loam type, and pH ranged from 6.8– 7.2 (Marasini et al., 2017). In this experiment, a total of 12 genotypes were used, where one genotype (AVTO1715) was a semi-determinate type, and remaining 11 genotypes were determinate types (Table 1). The disease resistance and susceptible genes of tomato genotypes to bacterial wilt, tomato yellow leaf curl, late blight, root-knot nematode and high pigment genes for lycopene and beta-carotene are listed in Table 2.

    Experimental design and plant cultivation

    The DoAR received the seeds of 12 genotypes from NHRC, Khumaltar and seeds were sown in nursery in the first week of October, 2021. Pusa Ruby, an open-pollinated determinate variety was used as check. About 30‐day-old seedlings were transplanted at the planting distance of 75 cm × 60 cm. Experimental treatments were laid out in randomized complete block design (RCBD) with three replications. Ten seedlings of each 12 genotypes were transplanted in the first week of November, 2021. Two rows were maintained at each plot, and each plot contained 10 plants with plot size (4.5 m2). The plot was fertilized at the rate of 25 MT/ha farm yard manure (FYM) and 200:150:120 kg N:P2O5:K2O/ha. All amount of FYM, phosphorous (P) and potassium (K), and half amount of nitrogen (N) were applied as basal one week before transplanting during the land preparation. Remaining half amount of N was top-dressed equally to the plants at 30 and 60 days after transplanting (DAT). Urea (46% N), diammonium phosphate (DAP, 18% N, 46% P2O5) and muriate of potash (MoP, 60% K2O) were used as the sources of fertilizers. Agromin (Aries Agro Ltd., India) at the rate of 2 ml/L was foliar sprayed 2 to 3 times uniformly in each plot to promote better plant growth. Cultural practices such as staking, hoeing, weeding, irrigation, topdressing and pruning were done as recommended by Gautam et al. (2021).

    Observations and statistical analysis

    Days to 50% flowering was taken as the number of DAT when 50% of plants in a plot begun to flower (anthesis). Plant vigor was recorded at flowering stage using a scale of 1 to 5 where: 1 = very weak, 2 = weak, 3 = medium or normal growth, 4 = vigorous and 5 = very vigorous (Gotame et al., 2019). Plant height (cm) was measured from joint of stem and root to terminal portion of the stem using meter scale at 50% fruit maturing stage. Fruit/plant (no.) was recorded in each harvest separately and estimated based on cumulative fruit number, and number of plants harvested. A total of three harvests were done until February and fruit weight of each plot was added in each harvest, then fruit yield (kg/plant) was estimated. The weight (g) of five individual fruit was taken using electronic digital balance and averaged. Fruit diameter (mm) was measured using digital Vernier caliper (150 mm, Model: DC- 515) and a scale ruler was used to measure the fruit pericarp thickness (cm). The fruit firmness (kg/cm2) was measured on five fruits using hand-held digital penetrometer (Lutron Model, FR-5120). Puncture tests were taken from the three equatorial sides of the same fruit and averaged. TSS (°Brix) was determined by digital refractometer (Model ATAGO, Tokyo, Japan). For each reading, the refractometer was washed with distilled water after use and dried with blotting paper to avoid contamination.

    The data were processed by MS Excel (version 16.0, Microsoft, Redmond, WA, USA) and then, one-way analysis of variance (ANOVA), genetic variability, and phenotypic correlation coefficients were computed using R program version 4.2.2 [R Core Team (2022), R: A language and environment for statistical computing, Vienna, Austria. URL https:///www.R-project.org/].

    RESULTS AND DISCUSSION

    Plant and fruit yield traits

    Result of ANOVA for plant and fruit yield traits of tomato genotypes are illustrated in Table 3. Days to 50% flowering was significant (P<0.05), but plant vigor was non-significant (P<0.05) among the genotypes. Highly significant (P<0.01) differences were observed in plant height. The tallest (231.3 cm) plants were measured in AVTO1715, while the shortest (85.1 cm) plant height was measured in AVTO1711. The plant height is a quantitative trait and controlled by many genes, and the variation observed in plant height could be due to genetic trait. The variation in plant height among tomato genotypes has also been published by Gotame et al. (2021). Tomato genotypes showed the significant (P<0.05) differences on the fruit number/plant. The highest (51.0/plant) fruit number was recorded in AVTO1008 which was statistically similar to AVTO1903 (46.0/plant), AVTO1715 (46.0/plant), AVTO1705 (44.0/plant) and AVTO1702 (33.0/plant). Dar and Sharma (2011) reported the highest fruit number (28.6/ plant) in CGNT-3 tomato variety and the minimum fruit number in PAU-2372 (10.6/plant), which is similar to our results. Our results are also similar to the findings of Ashrafuzzaman et al. (2010). Genotypic differences in fruit yield/plant were highly significant (P < 0 .01 ). AVTO1705 gave the highest (2.9 kg/plant) fruit yield among all genotypes, while Pusa Ruby produced the lowest yield (0.5 kg/plant). AVTO1921 produced the second highest yield of 2.7 kg/plant. Other two genotypes, AVTO1711 and AVTO1702 produced relatively high productions of 2.4 kg/plant and 2.0 kg/plant, respectively. Pusa Ruby is an early variety (data not shown) and this might be reason of producing the lowest yield. On the other hand, Pusa Ruby is an old variety, released in 1981 (Table 1) and its degeneration and deterioration might be attributed to low fruit yield. The phenotypic variability in fruit yield among tomato genotypes has been reported by many researchers (Sureshkumara et al., 2017;Hassan et al., 2021).

    Fruit weight and quality traits

    Results of the fruit weight and quality traits in different tomato genotypes are presented in Table 4. Genotypes showed the highly significant (P<0.01) differences in fruit weight and diameter. The AVTO1921 produced the heaviest (158.7 g) and biggest (94.6 mm) fruits, whereas the AVTO1715 produced the lightest (28.5 g) and smallest (38.9 mm) fruits. A wide range of variation in fruit width in tomato genotypes has been found by Hassan et al. (2021). The maximum average fruit weight (87.8 g) has been reported in genotype EC-35293 (Dar and Sharma, 2011). Genotypes revealed the significant (P<0.05) differences in fruit firmness, fruit pericarp thickness, and TSS. The highest fruit firmness (5.1 kg/cm2) was measured in AVTO1288, which was not statistically different from all the studied genotypes except for AVTO1903 (3.1 kg/cm2) and Pusa Ruby (1.3 kg/cm2). The thickest fruit pericarp (0.9 cm) was measured in Pusa Ruby, but it was statistically similar to AVTO1711 (0.8 cm), while the thinnest fruit pericarp (0.4 cm) were measured in AVTO1715 and AVTO1903. The highest TSS (3.3 °Brix) was recorded in AVTO1903 followed by AVTO1715 (3.0 °Brix), AVTO1008 (2.3 °Brix), AVTO1711 (2.3 °Brix), AVTO1288 (2.2 °Brix), and AVTO1909 (2.0 °Brix), while the lowest TSS (1.0 °Brix) was recorded in Pusa Ruby. Son et al. (2011) reported that TSS varied from 2.2 to 11.5 °Brix, however, in the present study, it ranged from 1.0 to 3.3°Brix. We found the highest TSS (3.3 °Brix) in AVTO1903, but Anisa et al. (2022) found maximum TSS (4.3 °Brix) in Gustavi variety. In this study, WorldVeg genotypes showed higher TSS than that of the commercial variety. Genotypes and maturity stages of the fruits determine the TSS content in tomatoes (Petrovic et al., 2022). The lower TSS observed in this study might be due to the fruits harvested at color breaking stage. Rawal et al. (2016) reported the variation in TSS among tomato genotypes at different harvesting stages. Likewise, Anisa et al. (2022) have reported the variation in fruit firmness, fruit pericarp thickness and TSS in tomato breeding lines.

    Genetic variability for plant and fruit yield traits

    Assessment of genetic variability for the plant and fruit yield traits in tomato genotypes is shown in Table 5. Among the 10 traits assessed, a wide range of variability was observed for plant height (70.0–245.0 cm), fruit weight (16.9–173.0 g) and fruit diameter (15.1–109.2 mm). This study observed lower genotypic variance than phenotypic variance for all the traits. The genotypic variance varied from 0.01 cm (fruit pericarp thickness) to 1,393.9 cm (plant height), whereas phenotypic variance ranged from 0.02 cm (fruit pericarp thickness) to 1,706.2 cm (plant height). The highest GCV value (52.2%) was estimated for fruit yield/plant and the lowest GCV (3.0%) was in plant vigor. However, PCV value was the highest (61.4%) for fruit number/plant and the lowest (7.3%) was for days to 50% flowering. Deshmukh et al. (1986) reported that PCV and GCV values greater than 20 % are regarded as high, values between 10% to 20% as medium and values less than 10% are considered as low. Accordingly, our study recorded the highest GCV for fruit yield (52.2%), fruit weight (42.8%), fruit number (31.7%), plant height (25.1%) and fruit diameter (24.6%), whereas medium GCV was recorded for fruit pericarp thickness (18.0%), fruit firmness (15.7%) and TSS (11.5%). Low GCV were recorded for days to 50% flowering (4.5%) and plant vigor (3.0%). Mohamed et al. (2012) reported high GCV for fruit number/plant, fruit weight, and yield/plant which agrees to our findings. Similarly, high PCV was estimated for fruit number (61.4%), fruit yield (57.3%), fruit weight (54.4%), TSS (46.2%), fruit firmness (36.9%), fruit diameter (29.8%) and fruit pericarp thickness (23.8%). High heritability was observed for the fruit yield/ plant (82.7%) and plant height (81.7%), whereas the fruit diameter (68.1%) and fruit weight (61.9%) showed moderately high heritability. TSS, plant vigor, fruit firmness, fruit number and days to 50% flowering showed low (<40%) heritability. Earlier researchers reported high heritability estimates for fruit yield/plant (Kumar et al., 2013;Saravanan et al., 2019) and plant height (Kumari et al., 2007). Fehr (1987) mentioned that heritability of a trait is determined by the population studied, the environment and the method used. High estimates of GA percent of mean were observed in the fruit yield (97.7), fruit weight (69.4), and plant height (46.7). Genetic advance mean (GAM) values ranged 0–10% were regarded as low, 10–20% as moderate and values more than 20% were considered as high GAM. We observed high heritability and GAM percent mean for the fruit yield/plant, plant height, and fruit weight, which are expected to give higher genetic gains in subsequent generations for breeding program. High heritability estimates for the fruit yield and plant height have also been reported by Mohamed et al. (2012). According to Kesumawati et al. (2022), the heritability values referred as the proportion of genotypic and phenotypic variance. Ahirwar et al. (2013) have stated high heritability estimates for fruit weight. GCV and heritability estimates provide a reliable indication of expected degree of improvement through selection.

    Correlation coefficient of phenotypic traits is presented in Table 6. The days to 50% flowering showed a significant (P<0.05) negative correlation with plant vigor (r = −0.39) and fruit yield (r = −0.52). The plant vigor showed a positive moderate correlation with the fruit yield (r = 0.39). The plant height showed a significant (P<0.01) positive strong relationship with the fruit diameter (r = 0.87). Fruit number/plant revealed a significant (P<0.05) positive association with the fruit yield (r = 0.40) and fruit diameter (r = 0.56) which indicates that through these traits, effective improvement in tomato can be achieved by simple selection. In contrast, fruit weight was significantly (P<0.05) negatively correlated with the fruit pericarp thickness (r = −0.47). A significant (P<0.05) positive correlation between the fruit number and fruit yield/plant has been reported by Kumar et al. (2013). Fruit weight showed a significant (P<0.05) positive correlation with the fruit diameter (r = 0.47) and pericarp thickness (r = 0.42). Kumar et al. (2013) mentioned that fruit diameter and fruit pericarp thickness showed a positive correlation with the fruit weight. The significant (P<0.05) association of plant vigor, fruit number, and fruit weight suggests that increase in any one of the traits may increase in fruit yield/plant which has also been reported by Ahirwar et al. (2013). High association between fruit number/plant and fruit yield/plant in tomato genotypes has also been mentioned by Al-Ballat and Al-Araby (2020). Similarly, fruit firmness showed a positive relationship with the fruit pericarp thickness (r = 0.46) and TSS (r = 0.48). In general, fruit firmness and fruit pericarp thickness associated with postharvest shelf life, high fruit firmness, and high pericarp thickness tend to have less water loss (Parker and Maalekuu, 2013). Likewise, fruit pericarp thickness showed a significant (P<0.05) negative correlation (r = − 0.38) with TSS.

    Conclusion and Recommendation

    This study evaluated 12 tomato genotypes (11 WorldVeg and one commercial variety of Nepal) based on phenotypic traits; days to 50% flowering, plant vigor, plant height, fruit number, fruit yield, fruit weight, fruit diameter and firmness, fruit pericarp thickness and TSS at western region of Nepal. The ANOVA of 10 morphological traits exhibited significant differences for all the traits except for the plant vigor. Out of 12 genotypes evaluated, the AVTO1705 was found to be high yielding (2.9 kg/plant). The PCV values are higher than GCV for the all the traits indicating the influence of environment. But the differences between PCV and GCV were less for the plant height and days to 50% flowering which indicates higher contribution of genotypic effect to express these traits. High heritability values for fruit yield and plant height indicates more genetic control rather than the environmental effect, and are recommended to be used as the selection criteria to tomato for high yield potential. Moreover, fruit number and fruit weight had a positive association with fruit yield, hence selection of these traits can improve the yield of tomato genotypes. Genotype AVTO1705 can be used in tomato breeding due to its high yielding trait. Furthermore, this line could be recommended for further evaluation in the farmer’s field.

    적 요

    본 연구는 2021년부터 2022년까지 네팔 테라이 지역에서 대만 세계채소연구소에서 육성한 토마토 우량 계통 11점과 네 팔 시판종 1 품종을 포함 12 품종의 유전적 다양성과 표현형 특성의 상관관계를 구명하기 위해 수행되었다.

    분산 분석결과는 식물체 세력을 제외한 모든 형질에서 계통 간에 유의성 있는 차이를 나타냈으며, 세계채소연구소 육성 계 통 AVTO1705은 네팔의 상업용 토마토 품종인 ‘Pusa Ruby’ (0.5 kg/주)보다 높은 수량(2.9 kg/주)을 보였다.

    표현형 변이 계수 (PCV)는 모든 형질에 대해 유전형 변이 계수 (GCV)보다 높았으며, 형질에 따라 아래와 같은 경향이 확인되었다. 1) 표현형 변이 계수 값은 착과수/주(개), 수확량 (kg/주) 및 과중(g/개)에서 최대를 보였다. 2) 표현형 변이 계 수, 유전형 변이 계수 및 유전적 고정도는 수량, 과중 및 초 장에서 높은 상가적 유전자 효과를 나타내었다. 3) 주당 수확 량 및 초장에 대한 높은 유전력은 품종 육성시 표현형 분석을 통해 선발이 가능할 것으로 판단되었다. 4) 수확량은 식물체 세력, 착과수 및 과중과 높은 정의 상관관계가 확인되었다.

    ACKNOWLEDGMENTS

    This study was supported by a grant from the “Asian Food and Agriculture Cooperation Initiative (AFACI), Rural Development Administration of Korea”, Republic of Korea. The authors would like to acknowledge WorldVeg Center, Taiwan for providing tomato germplasms to conduct this research.

    CONFLICT OF INTEREST

    The authors declare no conflicts of interest.

    Figure

    Table

    Name of genotypes, their sources/origins, pedigree and growth habits used in the experiment.

    -; not-available.

    Disease resistance, susceptible and pigment genes of WorldVeg tomato genotypes used in the experiment.

    <i>Bwr-12</i>; bacterial wilt resistance gene, <i>Ty-2</i>, <i>Ty-1</i>/<i>Ty-3</i>; tomato yellow leaf curl disease resistance genes, <i>Ph-2</i> and <i>Ph-3</i>; late blight resistance genes; +; homozygous resistant, –; homozygous susceptible, +/–; heterozygous, <i>Mi</i>; Root-knot resistance, and <i>Hp-1</i>; high pigment genes for lycopene and beta-carotene content. NT; not-tested.

    Plant and fruit yield traits of WorldVeg tomato genotypes evaluated at DoAR, Khajura, Lumbini Province, 2021–2022.

    Mean ± SD (n = 3). <sup>y</sup>Plant vigor (1-5); 1; very weak, 2; weak, 3; medium or normal growth; 4; vigorous and 5; very vigorous, <sup>NS</sup>; Non-significant at <i>P</i><0.05, *Significant at <i>P</i><0.05, **Highly significant at <i>P</i><0.01.

    Fruits weight and quality traits of WorldVeg tomato genotypes evaluated at DoAR, Khajura, Lumbini Province, 2021–2022.

    <sup>z</sup>Mean ± SD (n = 3); *Significant at <i>P</i><0.05; **Highly significant at <i>P</i><0.01.

    Genetic variability for plant and fruit yield traits in WorldVeg tomato genotypes evaluated at DoAR, Khajura, Lumbini Province, 2021–2022.

    SE; Standard error of mean, GCV; Genotypic coefficient of variation, PCV; Phenotypic coefficient of variation, GA; Genetic advance, DTF; Days to 50% flowering (day), PV; Plant vigor (1-5), PHT; Plant height (cm), FN; Fruit/plant (no.), FY; Fruit yield (kg/plant), FW; Fruit weight (g/plant), FD; Fruit diameter (mm), FF; Fruit firmness (kg/cm<sup>2</sup>), FPT; Fruit pericarp thickness (cm), and TSS; Total soluble solids (°Brix).

    Pearson’s correlation coefficients for 10 phenotypic traits in WorldVeg tomato genotypes evaluated at DoAR, Khajura, Lumbini Province, 2021–2022.

    *Significant at <i>P</i><0.05, **Highly significant at <i>P</i><0.01. DTF; Days to 50% flowering (day), PV; Plant vigor (1-5), PHT; Plant height (cm), FN; Fruit/plant (no.), FY; Fruit yield (kg/plant), FW; Fruit weight (g/fruit), FD; Fruit diameter (mm), FF, Fruit firmness (kg/cm<sup>2</sup>), FPT; Fruit pericarp thickness (cm), TSS; Total soluble solids (°Brix)

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