193 J. Hortl. Sci. Vol. 12(2) : 193-197, 2017 Inheritance of parthenocarpy in gynoecious cucumber (Cucumis sativus L.) cultivar PPC-2 G.S. Jat1, A.D. Munshi1, T.K. Behera1, *and C. Bhardwaj2 1Division of Vegetable Science, ICAR-Indian Agricultural Research Institute, New Delhi-12, India; 2Division of Genetics, ICAR-Indian Agricultural Research Institute, New Delhi-12, India *E-mail: tusar@rediffmail.com ABSTRACT The gynoecious and parthenocarpic inbred line, Pant Parthenocarpic Cucumber-2 (PPC- 2) was crossed with Indian monoecious and non-parthenocarpic cultivar Pusa Uday to develop F1, F2, B1 and B2 to determine the inheritance of parthenocarpy.The crop was grown under insect proof net house of 40 mesh. The pistillate buds were covered using butter paper bags before anthesis to prevent out-crossing.The observations were recorded separately for the development of early parthenocarpic fruits (i.e.1-7th nodes), late parthenocarpy (8th and above nodes) and non-parthenocarpic fruits. In F1 generation, out of 40 plants screened, 2 plants produced parthenocarpic fruits at lower nodes (1-7th nodes), 37 plants produced parthenocarpic fruits at upper nodes (8th and above), whereas,only 1 plant that did not produced any fruit was considered as non-parthenocarpic. The segregation of F2 population and test crosses for parthenocarpic fruit development suggested that parthenocarpy in gynoecious and parthenocarpic cucumber line PPC-2 is under the control of incomplete dominant gene. Keywords: Inheritance, parthenocarpy, gynoecious, cucumber INTRODUCTION Cucumber (Cucumis sativus L., 2n = 2x = 14) is an important valuable vegetable of Cucurbitaceae family. It is originated in India (Sebastian et al, 2010) fr om its wild progenitor Cucumis sativus var. hardwickii R., which is still found in southern foothills of Himalayas. It is primarily cultivated for tender fruits, which a r e used a s sa la d, pickles a nd rayata preparation. In India, cucumber is cultivated from higher altitude to plains under open field as well as under protected conditions. The cultivated cucumber has narrow genetic base with 3-8% polymorphism within the cultivated genotypes, and 10-25% between botanical varieties (Behera et al, 2011). India being considered the home of cucumber possesses a vast range of genetic diversity and variability for both growth and fruit characters, but this diversity has not been fully utilised for its genetic improvement. T he development of gynoecious va r ieties with parthenocarpic traits has become major challenge to the cucumber breeders for use as a parent in F1 hybrid development for achieving higher yield, earliness, uniformity and suitability for protected cultivation (Jat et al, 2015, 2016, 2017). Therefore, there is an important need to develop gynoecious hybrids with parthenocarpic traits, which may be utilized on commercial scale, especially in the north Indian plains because most of Indian cucumber cultivars are monoecious with non-parthenocarpic trait. Therefore, these varieties are not suitable for growing under protected conditions as these require pollination for fruit set. Gynoecy coupled with parthenocarpic cucumber is a yield and quality-related parameter and a high value vegetable crop immensely suited for off season cultiva tion under pr otected condition beca use parthenocarpic varieties do not require pollination for fruit setting. Moreover, the fruits are mild in flavour, seedless and have thin skin that does not require peeling. Plant growth regulators also regulate the parthenocarpic trait and its stability is significantly influenced by environmental factors. It is a complex physiological process that can be influenced by environmental, physiological and genetic factors. Some studies indicated that low temperature, light and Short Communication 194 J. Hortl. Sci. Vol. 12(2) : 193-197, 2017 Jat et al exogenous hormone could induce parthenocarpy. However, the genetic mechanism of parthenocarpy in cucumber is still unclear. The information about genetics of parthenocarpy is utmost important for efficient breeding procedure to be used for the development of stable parthenocarpic lines. Keeping in view all above facts and realizing the importance of cucumber as an important vegetable crop for protected cultivation, it was felt crucial to conduct an experiment for inheritance of parthenocarpy in cross of gynoecious parthenocarpic line with Indian monoecious non- parthenocarpic line. The gynoecious line PPC-2 (used as a female parent for source of parthenocarpic gene) was crossed with monoecious and non-parthenocarpic line Pusa Uday (used as male parent) to develop F1 hybrid during August-November, 2012. The resulting F1 generation of the cross PPC-2× Pusa Uday was selfed to obtain F2 seeds and pollinated simultaneously with P1 (PPC- 2) a nd P 2 (Pusa Uda y) to genera te ba ckcr oss generations, B1 and B2, respectively, during August- November, 2013. The seed material of all segregating and backcross generations (F2, B1and B2) including parental lines and F1were sown in plug trays using soil less media i.e. coco-peat, vermiculite and perlite in 3:1:1 ratio. The seedlings at three leaf stage were transplanted in insect proof net-house of 40 mesh size during March-June, 2014 at the Research Farm, Centre for Protected Cultivation Technology, ICAR-Indian Agricultural Research Institute, Pusa Campus, New Delhi, India. All plants of segregating generations (F2, B1 and B2) along with parents and F1 hybrids were tagged and numbered after transplanting for their individual identity for parthenocarpic fruit development. The F2 population comprising 213 plants were used for genetics of parthenocarpy in background of gynoecious and parthenocarpic inbred line PPC-2. The female flowers were covered with butter paper bag one day prior to anthesis to maintain isolation. The fruit set and development were examined after at 7 to 8 days after flower opening. The number of parthenocarpic fruits developed and total number of female flowers labelled per plant were counted. Observations were recorded for development of parthenocarpic fruits up to 25th nodes. Plants that produced parthenocarpic fruits up to 25th node were considered as parthenocarpic plants. Observations were recorded separately for early parthenocarpy (1- 7th node), late parthenocarpy (8th and above node) and non-parthenocarpy. The goodness of fit of the observed segregation ratio for the segregation of parthenocarpic and non- parthenocarpic plants was tested using the classical Chi-square (χ-2) test as suggested by Panse and Sukhatme (1985). The χ-2 value was calculated using the formula given below. χ-2= (Observed number – Expected number) 2 / Expected number) The test of significance is judged when the computed χ2 statistic exceeds the critical value in the table for a 0.05 probability level, then we can reject the null hypothesis of equal distributions and then it is revealed that the observed values are the same as the theoretical distribution. Parthenocapy is an important yield related trait in cucumber, especially in protected cultivation. In the present study, an attempt was made to consign the inheritance of parthenocarpy on classical dominant- recessive Mendelian model by keeping the cucumber fruits only in three categories of their fruit development i.e. early parthenocarpic, late parthenocarpic and non- parthenocarpic fruit development. The development of parthenocarpic fruit in ‘Pant Parthenocarpic Cucumber-2 (PPC-2)’ is taking place from the beginning at the lower nodes from the base of the plant (early parthenocarpy). Therefore, ‘PPC- 2’ was considered as a homozygous genotype for parthenocarpic fruits development. The variety Pusa Uda y wa s monoecious a nd pr oduced non- parthenocarpic fruits and it was considered to be homozygous for non-parthenocarpic fruit development. The F1 hybrid derived from the cross of PPC-2 × Pusa Uday with heterozygous condition produced some parthenocarpic fruits on the lower nodes i.e.5-7th node a nd a bove 8 th node, wer e consider ed a s la te parthenocarpic fruits. In F1 generation, most of the plants produced parthenocarpic fruits but some plants that did not set any fruit were considered as non- parthenocarpic fruit. In segregating F2population, early, late and non-parthenocarpic plants were recorded. Out of 213 plants, 170 produced as early and late pa r thenoca r pic fr uits wher e a s 43 a s non- parthenocarpic fruits. The χ2 value indicated a good fit for segregation of parthenocarpy (early, late and non- 195 Parthenocarpy in cucumber cv. PPC-2 parthenocarpy) in the F2 population and backcrossed populations confirmed with the expected ratio of 1:2:1 a nd 1:1, respectively (Table1). Therefor e, the genotypes for inbr ed line PPC-2 r epr esenting pa r thenoca r py, non-pa r thenoca r py a nd la te parthenocarpy phenotypes were considered as PP, pp and Pp, respectively. These data support that parthenocarpic trait in cucumber is controlled by single incompletely dominant gene, as suggested by Pike and Peterson (1969). They had used a parthenocarpic monoecious var iety a nd a non-pa r thenoca r pic gynoecious line as parents, whereas in our study, gynoecious parthenocarpic and monoecious non- parthenocarpic inbred lines were used as parents. Average first fruiting node in segregating generation was observed at the 5thnode. Rudish et al (1977) also suggested that the degree or intensity of parthenocarpy could be measured by both the earliness of fruiting and the total number of parthenocarpic fruits. The segregation for parthenocarpic fruits observed in F2 population of PPC-2 × Pusa Uday is shown in Fig.1. These data support that parthenocarpic trait in cucumber is controlled by single incompletely dominant gene, as suggested by Pike and Peterson (1969). Exploring the parthenocarpic trait for development of high yielding cultivars and F1 hybrids suitable for protected cultivation is one of the current priority areas of cucumber breeding.The breeding procedure for development of parthenocarpic varieties in cucumber is not well understood because of the complexity in nature of inheritance and involvement of physiological factors for parthenocarpic fruit development(Wu et al, 2016). In cucumber, parthenocarpic mutants have been largely used to breed cultivars suitable for greenhouse cultivation. It was also clear that parthenocarpy trait is genetically controlled, but there is some argument regarding the number of genes and type of gene action involved in development of parthenocarpic fruits. Parthenocarpy in cucumber is controlled by an incomplete dominant gene P (Pike and Peterson, 1969; Kim et al, 1992). In the homozygous condition PP develops early parthenocarpic fruits generally at fifth node. In the heterozygous condition Pp produce parthenocarpic fruits later than homozygous plants and small in numbers. In homozygous condition recessive pp develops non-parthenocarpic fruits. Single recessive gene might be responsible for the expression of parthenocarpy in cucumber (Juldasheva, 1973) or many incompletely recessive genes control parthenocarpy (Kvasnikov et al, 1970). The study of F3 population showed that more than five genes are involved in par thenocarpy, whereas growing envir onmental conditions and epistatic interactions significantly influence the expression of this trait (Sun et al, 2006 a and b) and two additive-dominant epistatic major genes and additive-dominant polygenes (Li et al, 2012). Thus, the parthenocarpic line PPC-2 could be utilized for development of light green parthenocarpic cucumber lines using pedigree method of breeding (hybridization followed by selection of pur e homozygous parthenocarpic lines). It was revealed from the present study that parthenocarpy in cucumber particularly in gynoecious and parthenocarpic lines PPC-2 is governed by incomplete dominant gene. This study has to be Generations Number of Early Late Non- Expected Chi- P- plants parthenocarpic parthenocarpic parthenocarpy ratio square value (1-7th nodes) (8th and above nodes) Observed Expected Observed Expected Observed Expected PPC-2 (P1) 40 40 40 - - - - - - - Pusa Uday (P2) 40 - - - - 40 40 - - - PPC-2 × Pusa Uday (F1) 40 2 - 37 40 1 - - - - PPC-2 × Pusa Uday (F2) 213 49 56 121 105 43 52 3:1 0.94 0.23 (PPC-2 × Pusa Uday) × 40 23 20 17 20 - - 1:1 - - PPC-2 (B1) (PPC-2 × Pusa Uday) × 40 - - 24 22 16 18 - - - Pusa Uday (B2) Table 1. Segregation for parthenocarpy in cucumber J. Hortl. Sci. Vol. 12(2) : 193-197, 2017 196 Fig. 1. Phenotypic evaluation of parthenocarpic and non-parthenocarpic parental genotypes, F1 and F2 population (PPC-2 × PusaUday) of cultivated Cucumis sativus for parthenocarpy, (a) parthenocarpic fruit of PPC-2, (b) non-parthenocarpic fruit of Pusa Uday, (c) parthenocarpic fruits of F1 of PPC-2 × Pusa Uday, (d-f) showing segregation for parthenocarpy in F2 population, (d) early parthenocarpic fruit development, (e) late parthenocarpic fruit development, (f) seeded fruit (after pollination). J. Hortl. Sci. Vol. 12(2) : 193-197, 2017 Jat et al continued further by employing more number of populations in different cross-combinations and plants in segregating population in different environment and locations and confirmation of genetics for this trait would be required in other potential parthenocarpic lines. 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