**2.1 Genetics of quantitative and qualitative characters**

The deep understanding about cucumber crops biology was only possible due to mendelian's classical genetics which have made possible for the cucumber breeders to develop improved varieties and F1 hybrids. The knowledge about different genes which affects economic traits facilitated breeders to develop proper genetic resources for the development of trait specific genetic stock for further use for genetic improvement of cucumber. For example, the size of the population will be much smaller if a breeder is selecting for a trait controlled by a single gene, than if the trait is controlled by multiple genes with a large environmental influence. The application of Mendelian genetics using classical techniques in cucumber has facilitated the discovery of a number of genes for yield, quality, plant architecture, and disease and pest resistance in both slicing and pickling cucumber. The yield in

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**2.4 Fruit characters**

*Classical Genetics and Traditional Breeding in Cucumber (*Cucumis sativus *L.)*

cucumber is enhanced by utilizing gynoecious as one of the parent in breeding programme which promote higher female to male sex ratio. Sex ratio (female: male), fruit weight and fruit size are the direct yield components in cucumber breeding.

In commercial cucumber cultivars, the type of sex forms (gynoecious or monoecious) and the amount of their expression is important because these have a direct effect on harvesting date, production and productivity of this crop. Flowering time in cucumber played a critical role in fetching early market price and increase in fruit yield for the growers. In cucumber, the type of sex from (gynoecious or monoecious) and the amount of their expression have direct effect on harvesting time, production and productivity. The sex expression also played a vital role in seed production as well as development of new plant types. The flowering traits like node number at which first female flower appear, days to first pistillate flower opening, and male: female (♂:♀) flower ratio (sex ratio) are the important traits for determination of earliness and fruit yield. The sex expression in cucumber is controlled by three genes, *F*, *M*, and *A* [31]. The degree of female flower expression is controlled by *F/f* gene [31, 32]. The *F* locus determines the amount of femaleness (*FF* > *Ff* > *ff*). Gynoecious sex expression in F1 hybrid of cross of gynoecious × monoecious is governed by partial dominance ([33]; Perl-Treves and Rajagopalan [34] where as in gynoecious × subandroecious, it was governed by multiple genes [35]. single gene with dominant or incomplete dominance [36], single dominant gene [8, 37–39] and oligogene with some modified genes [40], three major QTLs conferring subgynoecy in cucumbers [41]. Seven gynoecious QTLs were detected on chromosomes 5 and 6 in backcross population [42]. These studies suggested that gynoecious is an important economic trait for determinant of earliness and yield in

The discovery of parthenocarpy in cucumber has led to the development of seedless fruit in combination with gynoecious trait. Gynoecy coupled with parthenocarpy is a yield and quality related parameter and a high value vegetable crop suited for protected cultivation because these varieties do not require pollination for fruit setting. The fruits of greenhouse parthenocarpic cucumber varieties are also mild in flavor, seedless and have a thin skin that does not require peeling. Still the genetics of parthenocarpy is not well understood in cucumber which is utmost important for efficient breeding procedure. Pike and Peterson [43]; Kim et al. [44] and Jat et al. [38] suggested that an incomplete dominant gene is responsible for parthenocarpic fruit development. Single recessive gene is responsible for parthenocarpy in cucumber [45]. The growing environmental conditions and epistatic interactions influence the parthenocarpy trait [46, 47] and two additive dominant epistatic major genes and additive dominant polygenes [35]. Seven QTLs for parthenocarpy were detected on chromosome 5 and 7 (*parth5.1* and *parth7.1*) and two on chromosome 6 (*parth6.1* and *parth6.2*) [48]. One major effect QTL (parth 2.1) was identified controlling parthenocarpy [49, 50]. The identification of QTLs is a valuable resource for cucum-

The improvement in fruit traits including shape, size, and color is an important target in cucumber breeding. The fruit traits like fruit weight, length diameter and

ber breeders for development of parthenocarpic cultivars.

*DOI: http://dx.doi.org/10.5772/intechopen.97593*

**2.2 Sex expression**

cucumber.

**2.3 Parthenocarpy**

cucumber is enhanced by utilizing gynoecious as one of the parent in breeding programme which promote higher female to male sex ratio. Sex ratio (female: male), fruit weight and fruit size are the direct yield components in cucumber breeding.
