**1. Introduction**

Cucumber (*Cucumis sativus* L) is an important vine species of the Cucurbitaceae family. Cucumber is the fourth most important vegetable crop worldwide and is a model system for other Cucurbitaceae family which is used for studying several significant biological processes [1]. Cucumber is originated from India, particularly southern foot-hills of Himalayan region. It was domesticated in India from its wild relative, *Cucumis sativus* var. *hardwickii* 3000 years ago [2, 3]. It is commercially grown in the tropical and subtropical regions of the world. The fruits are widely consumed as salad at immature stage. Cucumber is high in water content and low in calories, fat, cholesterol, and sodium [4] and good source of mineral nutrients (Ca, Mg, P & K) and medicinal properties such as antioxidant, anti-inflammatory, and

anti-cancer benefits. Cucumbers are also used for digestive benefits and mood stability when modulating stress. Cucumbers fortify cells so they may retain hydrated and work at the highest levels, and may slow age-related cellular deteriorations [5]. The available genetic diversity within the cultivated cucumber is very low [2, 6–9] which is the major impediment in the genetic improvement of various cucumber market classes [10]. Thus, increasing the genetic diversity of cultivated cucumber is an important task for public sector research [11]. The cultivated cucumber has narrow genetic base with 3–8% polymorphism within the cultivated genotypes, and 10–25% between botanical varieties [12]. Earliness, high yield, uniform fruit shape, size, color and better quality are prerequisites for the release of the cucumber varieties and F1 hybrids for open field condition. In addition to these characters, gynoecious and parthenocarpic traits are desirable for green house cucumber production. Identification of genotypes tolerance to drought is also one of important breeding objective in cucumber [13]. Cucumber is a monoecious vegetable crops species. However, several gynoecious varieties and F1 hybrids have been developed by introgression of *F* locus (gynoecious gene) in the background of different market classes of the cucumber for commercial production. The utilization of gynoecious lines are economical and easier for hybrid seed production by reducing the cost of male flower pinching and hand pollination [14]. The present day cucumber F1 hybrids for open field production derived from the cross between gynoecious × monoecious and monoecious × monoecious where as green house grown F1 hybrids are the result of the cross of gynoecious × gynoecious lines with parthenocarpic traits. The evaluation and selection of the genotypes only based on phenotype characters for high yield and stability of gynoecious sex form require many years in multiple environments which is very expensive and time consuming process. The whole genome sequencing in cucumber [15] have opened the way to utilize the DNA markers viz. simple sequence repeats (SSRs) for gene mapping, marker assisted selection and marker trait association for several economic traits in cucumber [16–18]. With the development of high density linkage map several traits have been mapped in cucumber including, flowering time [19] fruit quality [20], diseases [17, 21], yield [22], fruit spines [23], fruit color [8], chromosomal mapping and QTL analysis of resistance to downy mildew [24–26], yellow fruit flesh [27], pleiotropic andromonoecy and carpel number [28, 29]. QTLs have been identified in Sikkim cucumber (*Cucumis sativus* var. *sikkimensis*) for important horticultural traits including flowering time, fruit size, flesh thickness, fruit spines, fruit color [30].
