Background

Cucumber (Cucumis sativus Linn.) is an important vegetable crop cultivated on commercial scale during summer season in northern India. It belongs to family cucurbitaceae, and its primary centre of origin is India. Cucumber has been cultivated in India for at least three thousand years (Zeven et al., 1982). The economic importance and growing popularity of the crop has stimulated breeding work aiming to improve the quantitative and qualitative traits of the crop. The improvement of the characteristics especially the polygenically controlled ones like yield and its components, depends largely upon the extent of genetic variation, its transmissibility (heritability) and nature of response to selection (genetic advance). The knowledge of correlation among quantitative characters like yield and its components is also valuable because selection based on one trait may directly or indirectly affect the performance of another trait. Further, the magnitude of heterosis provides a basis for genetic diversity and a guide to the choice of desirable parents for development of superior F₁ hybrids so as to exploit hybrid vigour and for building better gene pool to be employed in population improvement. In cucumber development and evaluation of hybrids will be rewarding keeping in view wide genetic variation available for yield and its contributing traits. Therefore the present investigation was carried out to study the general combining ability, specific combining ability effects and the extent of heterosis in F₁ hybrids over better parent and standard check for improvement of yield and its contributing traits.

1 Results and Discussion

The analysis of variance for combining ability for all characters showed that mean squares due to general combining ability (gca) and specific combining ability (sca) effects were significant for all characters except node at which first female flower appears and equatorial diameter of fruit.

Studies on general combining ability had successfully led to making choice of suitable parents. The knowledge on fruit yield and its components would show wide scope for proper classification of parental lines. On the basis of gca effect (Table 1), parent ACC-8 for diameter of fruit and average fruit yield, ACC-2 for days to first fruit harvest and number of fruits per vine, and ACC-4 for average fruit weight were found to be the best general combiner. The genotypic difference of gca effects for different traits have also been observed by Singh et al.,1999 and Singh et al., 1999.

The three best performing crosses showed highest specific combining ability effect in order of merit were ACC-2×ACC-6, ACC-5×ACC-6, ACC-7×ACC-8 for days taken to first fruit harvest; ACC-4×ACC-7, ACC-4×ACC-5, ACC-3×ACC-5 for number of fruits per vine; ACC-3×ACC-8, ACC-1×ACC-4, ACC-6× ACC-8 for average fruit weight; ACC-3×ACC-4, ACC-5×ACC-6, ACC-2×ACC-3 for diameter of fruit; ACC-1×ACC-4, ACC-2×ACC-4, ACC-2×ACC-6 for average fruit yield (Table 2). More or less these results were similar to the findings of El-Hafez et al., 1997, Mushi et al., 2006 and Bairagi et al., 2005. From the present study, it is evident that the best cross combinations for most of the characters generally involved one good and one poor general combiner with high sca effects, may be due to a complimentary gene action which can be fixed in the segregating generation. On the contrary, crosses with high sca effects involving parents low x low combiners may be used for exploring of hybrid as the non-additive, non-fixable genes seems to play a major role.

Magnitude of heterosis over the BP (better parent) and SC (standard check) for different characters was estimated and given in Table 3. For days taken to first fruit harvest, the extent of heterosis varied from -14.31 to 18.27 over BP and -21.26 to 2.24 over SC. Thirteen cross-combinations showed significant negative heterosis over BP and all the hybrids registered significant negative heterosis over check. The hybrid ACC-2×ACC-6 and ACC-5×ACC-7 exhibited maximum heterosis over BP and SC, respectively. Number of fruits per vine is a well recognized yield attributing character and prime objective of any breeding programme. The observed range for number of fruits per vine was -28.15 to 32.15 over BP and -17.80 to 35.17 over SC. There were seven and seventeen hybrids which showed significant positive heterosis over BP and SC, respectively. Cross-combinations ACC-3×ACC-4 and ACC-2×ACC-8 exhibited maximum heterosis over BP and SC, respectively.

The extent of heterosis for average fruit weight ranged from -45.17 to 35.15 over BP and -35.14 to 14.19 over SC. Six hybrids were possessing significant heterosis over BP and eleven hybrids over SC. Cross ACC-3×ACC-8 showed maximum heterosis over BP and ACC-4×ACC-6 exhibited highest value over SC. Data for diameter of fruit revealed that the magnitude of heterosis ranged from -24.10 to 54.34 over BP and -14.28 to 27.27 over SC. Seven and five cross combinations exhibited significant negative heterosis over BP and SC, respectively. Hybrid ACC-6×ACC-7 and ACC-4×ACC-6 showed maximum heterosis over BP and SC, respectively. Heterosis over BP and SC for number of fruits varied -17.18 to 16.33 and -22.12 to 26.21. Twelve hybrids showed significant positive heterosis and maximum heterosis over BP was shown by ACC-1×ACC-8 while, ten hybrids registered significant positive heterosis over SC and maximum heterosis was observed for cross combination ACC-5×ACC-6. Heterosis over better parent for average yield varied from -37.15 to 17.55. Only eight hybrids showed significant positive heterosis over BP and it was recorded maximum for ACC-2×ACC-4 while, heterosis over standard check ranged from -37.51 to 39.25. All hybrids showed significant negative heterosis over SC except six hybrids and it was registered maximum by cross combination ACC-1×ACC-4. These results are in agreement with the earlier findings of Bairagi et al., 2005, Lower et al., 1982, Frederick and Staub, 1989 and Vijayakumari et al., 1993. The highest positive indirect effects on yield/plant were the number of pods/plant (2.834), followed by the number of branches/plant (2.387), the number of seeds/plant (1.963), 100-seed weight (1.452), pod length (1.225), and days to 50% flowering (0.897). In contrast, days to maturity (-1.581) exhibited the greatest negative indirect effect on yield/plant, followed by days to first flowering (-0.991), pod length (-0.772), and plant height (-0.749). The number of branches/plant (0.851), the number of pods/plant (0.988), the number of seeds/plant (0.988) and 100-seed weight (0.634), were all positively and highly significantly correlated with yield/plant (Table 3). Days to first flowering (-0.112) and days to 50% flowering (-0.143), plant height (-0.061), days to maturity (-0.551) and the number of seeds/pod (0.209), were all negatively correlated with yield (Table 3), however, none of them were significant.

2 Material and Methods

The present investigation was conducted in the Department of Vegetable Crops, Punjab Agricultural University, Ludhiana. The material for the study comprised of 8 inbred lines. During first year, crosses were attempted among inbreds by following diallel mating system. The parents were also grown for further maintenance and were selfed simultaneously. The 28 F₁ hybrids along with 8 inbred parents and a standard check Punjab Naveen were sown and evaluated for heterosis and combining ability during second year. During both years, nursery was raised in plastic bags. Seedlings were transplanted in middle of March on beds spaced at 1.5 m apart with plant to plant spacing 45 cm. Observations for days taken to first fruit harvest, number of fruits per vine, average fruit weight, diameter of fruit, and average fruit yield were worked out on the basis of five plants per replication and there were three replications in randomized complete block design. The magnitude of heterosis was calculated as per cent increase or decreases over better and check parent for each treatment. The general and specific combining ability and their effects were computed by method (fixed effect model) as suggested by Griffing, 1956.

Authors’ contributions

GS carried out genetic studies and performed the statistical analysis. PSB is guide of GS and help in planning and layout of experiment. RKD conceived of the study, participated in its design and drafts the manuscript.

References

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EL-Hafez A.A., Sayed S.F., and Gharib A.A., 1997, Genetic analysis of cucumber yield and its components by diallel crossing, Egyption Journal of Horticulture, 24: 141-159

Frederick L.R. and Staub J.E., 1989, Combining ability analysis of fruit yield and quality in near homozygous lines derived from cucumber, Journal of the American Society of Horticultural Science, 114: 332-338

Griffing B.,1956, Concept of general and specific combining ability in diallel cross system, Australian Journal of Biological Science, 9: 463-493

https://doi.org/10.1071/BI9560463

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Singh A.K., Gautam N.C., Singh R.D., and Singh B.P., 1999, Heterosis and inbreeding depression in Cucumber (Cucumis sativus Linn.), Progressive Horticulture, 31: 74-78

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Zeven A.C., and Deweb M.J., 1982, Dictionary of cultivated plats and regions of diversity, pp 259