Genetic System of Cucumis sativus var. hardwickii (Royle) Alef. – (wild cucumber) in Jammu, J&K,

A small population of Cucumis sativus var. hardwickii (wild cucumber) has been localized for the rst time from Billawar, Kathua (District) in UT of J&K. This variety as expected is monoecious in sex expression, but shows unique pattern of development of male and female owers on the vine throughout its blooming period. Keeping provision for both both self and cross pollination, it is found to be self compatible, insect pollinated taxa with high reproductive output and a stable diploid complement (2n = 14). Small proportion of cells (9.92%) shows tetraploidy (2n = 28). The species exhibits high and healthy fruit set on open pollination as well as on manual self and cross pollination.


Introduction
Genus Cucumis is distributed in tropical region with 52 species (Mabberley, 2008). This genus is of horticultural value as it has many cultivated species. Total six species of Cucumis are present in India (Chakravarty, 1982), of which Cucumis sativus L. is cultivated on large scale for its edible fruit. Its wild botanical variety i.e.-C.sativus var. hardwickii is rare and is reported to possess unique morphoagronomic characters as well as resistance against pest, root knot nematodes (Walters et al., 1997), cucumber green mottle mosaic virus (Hore and Sharma, 1996) and downy mildew diseases (Staub and Palmer, 1987). In India, it has been reported from the foot hills of Himalayas (Charakravarthy, 1982: Deakin,1971) and in higher elevation of different states such as Chattishgarh, Himachal Pradesh, Uttar Pradesh, Rajasthan, Madhya Pradesh, Maharastra and Odisha (Dikshit, 2014). Present communication elaborates the genetic system of this variety based on observations on a small population sprawling at Billawar, Kathua in the UT of J&K. India.

Material And Methods
Present investigation was carried on wild variety of cucumber i.e. Cucumis sativus var. hardwickii. The variety has been collected by us from Billawar, District -Kathua of UT of J&K (Fig. 1a). The region of occurrence is characterized by high hills dominated by mostly Pinus trees at an altitude of 32°28 26 N and 75°24 5 . Total 11 plants were observed at this site during our rst eld visits to Billawar and its adjoining areas in 2018. All vines were tagged for studying various features such as vine length, number of branches/vine, number of leaves/branch and number of owers per in orescence. Flowers were collected randomly from the vines to study various morphological features. Vines were regularly monitored throughout the season to determine their sex expression and timing of appearance of male and female owers and their unique pattern of development on the vine.
For determining the reproductive e ciency, few mature and unopened female owers were tagged and left as such for allowing pollination as it occurs in nature. These were monitored after somedays to check fruit set on open pollination. Apomixis was checked by bagging few mature but unopened female owers, that were left undisturbed to check %fruit set. To check the %age fruit set on hand self and cross pollination, some female owers were hand pollinated with pollen from male owers of same vine and from different vine. These female owers were bagged and observed after somedays to check fruit set on manual self -pollination and cross-pollination. %age fruit set on open and hand Self and Cross pollination was calculated as under :-For evaluating the meiosis, young male oral buds of these were xed in mixture of 3 parts of ethyl alcohol and 1 part of acetic acid for studying Pmc meiosis. After 24 h of xation, the oral buds were washed in water and preserved in 70% ethyl alcohol. Finally, the anthers were squashed in 1% propiocarmine to study pmc meiosis. Female ower are also yellow in colour, 2.19cm ± 0.56 in length with highly papillioneous stigma and small swollen ovary averaging 1.50cm ± 0.04in length (Fig. 1f &g)). Ovary is covered with numerous trichomes which provide protection to the fruit against herbivory during maturity. At the base of short style, cup shaped nectary disc is present that produces maximum nectar during early hours of the day.

Results
Both male and female owers exhibit unique arrangement on the vine (Fig. 1m). Male owers are rst to appear and open on lower nodes (either 1st or 2nd ) of the vine in the rst week of September (Day = 15-20th after seed germination). Thereafter, about 10-12 owers appear on the upper nodes such as on second, third, fourth node and so on the main branch of the vine. These owers open and shed their pollen unnecessarily before the rst ower differentiates/opens. The time gap between the initiation of staminate and pistillate phase is around 10-12 days. 1st female ower appears and opens on 3/4th node and both male and female owers co-occur on these nodes. Second female ower appears on either 13th or 14th node, after a time gap of 3-4 days of opening of 1st female ower. Thereafter owers differentiate both on middle and upper node while the sequence of male owers is continuous on nodes toward the upper end. Peak owering period of both & owers was recorded during the mid of September. Staminate phase was observed during the rst two weeks of September for 10-15 days when owering initiation occur on the vine, followed by co-occurrence of both staminate and pistillate phase for longer period i.e. around 30-40 days. At the end of owering period in last week of October, only staminate phase was observed with no female owers and thereafter plants starts drying. This nding was found to be contrast with Shifriss (1961) where staminate phase is followed by co -occurrence of both male and female owers and nally pistillate phase ( Table 1).
Ratio of male to female owers through out the season reteriated the above observation. Just after the completion of vegetative growth, vine undergoes owering with maximum production of male owers and no female owers and their ratio was found to be 16:0 ( : owers) and the same was observed for 10-12 days. In the mid of life cycle of vine, ratio was found to be around 24:4 ( : owers) at this time, when maximum fruit production occurred ( Table 1). The ratio again changes toward the end of owering period when number of female owers starts decreasing. It was recorded as 20:2 in mid October and in the nal phase, it was recorded as 14:0 (Last week of October). High reproductive output was observed in wild form of cucumber in term of %age fruit set. On open pollination, fruit set averages 85% and all the fruits were healthy and uniform in size averaging 38.76gm in weight. Fruit is whitish green in colour when young and small in size averaging 4.2cm ± 0.08 ×4.3cm ± 0.02 (Fig. 1i).Few female owers were hand pollinated from the male owers of same and different vines and then bagged. Their % fruit set was found to 75% & 80%, and their weight averages 37.76 and 35.52 respectively. On bagging female owers (about to open), no fruit set was observed. This ruled out the role of apomixis in this species.
PMCs meiosis was also studied in C. sativus var. hardwickii to know the chromosome count by xing the young oral male bud randomly from the different vines. Pollen mother cells at Metaphase -I revealed the presence of 7 bivalents showing diploid chromosome number for the the variety as 2n = 14 (Fig. 1J).
Total 75 pmcs were scanned for meiosis. Of these, 52 pmcs (69.33%) had seven perfect bivalents at Metaphase -I (Fig. 1J) and remaining 14 pmcs (18.66%) showed equal segregation of chromosomes 7:7 at each poles at Anaphase I (Fig. 1l). Few pmcs (9.33%) showed 14 bivalents at Metaphase I (Fig. 1k) indicating the presence of polyploidy in this species. The presence of 14IIs in few cells and seven perfect bivalents in maximum pmcs indicates cytologically stable nature of the variety.

Discusssion
Cucumis sativus var. hardwickii (wild cucumber) is self compatible, insect-pollinated taxon with stable genome (2n = 14) and high reproductive output (85%) as compared to cultivated cucumber (73.3%) (Choudhary and Damke, 2015;Dikshit, 2014). Flowering in this wild variety initiates with the appearance of male ower after 10-12 days of seed germination followed by co-occurrence of both male and female ower. The male owers predominated during the owering phase. During the early phase of owering period, the ratio of male and female ower (16:0) is less, maximum during peak blooming period (24:4) and again decreases (14:0) toward the end of owering period. Once the vine starts setting fruits, the number of pistillate ower goes on decreasing and only staminate owers continue to differentiate upto to the end of lifespan of the vine. Our observations are in accordance with the ndings of Delaplane and Mayer (2000) in cultivated cucumber. These ratio of male to female owers and time of emergence of male and female after the seed germination varies from species to species and might be in uenced by environmental condition and depend on plant growth and vigour.
Cytologically, wild variety of cultivated cucumber is stable in nature with diploid chromosome number of 2n = 14 at Metaphase -I and equal segregation of chromosomes (7:7) at Anaphase I. This stable chromosome number was also reported by Singh and Roy (1974) and Rajkumari et al., (2013). But the existence of tetraploid cells in this wild variety of cucumber is not on record.
In relation to reproductive e ciency, wild variety of cultivated cucumber has high %age fruit set These ndings was also reported by Choudhary and Damke in 2015. Reason might be large number of lateral branches(7-8) in wild cucumber as compared to cultivate cucumber (3-5).
Cultivated varieties of cucumber match with their wilder counterpart in being self compatible and in having diploid chromosome number of 2n = 14. However the cultivated forms show abnormalities in Pmc meiosis in terms of quadrivalent and hexavalent formation and in having hypoploid and hyperploids cells. These also have comparatively low %age fruit set (73.35) (Previous observation unpublished).

Conclusion
This wild cucumber exhibits more lateral branches, more number of female owers as a results high reproductive output (85%) as compared to the cultivated cucumber (73.3%).In view of these characters, genetic base of this plant can be used in cultivated cucumber by various hybridization techniques for crop better improvement.

Declarations
Aknowledgements: One of the author "Priya Sharma" is thankful to the UGC-SAP for nancial assistance.
Con icts of Interest: Authors have no con icts of interest over the publication of this research paper.