**3.1 Traditional breeding objectives and achievements**

The development of high yielding cultivars with better fruit quality is the major goal of cucumber breeding programs across the globe. Due to the introgression of gynoecious sex form in the background of different cucumber market classes, the development of varieties with earliness characters along with high female: male flowers ratio is also an important objective for cucumber breeding. Therefore, rapid advancement has been made in the development of gynoecious and parthenocarpic cucumber lines/varieties suitable for green house cultivation. Cucumber breeders have developed several genetic stocks for pest and disease resistance. The introgression of pest and disease resistance gene from available sources should be the prime goal for most of the cucumber breeding programmes in future for the development of multiple disease resistance (MDR) varieties including virus resistance. The various fruit quality traits have been selected in cucumber depending on regional preference of the consumers. These quality traits include fruit size, shape (length and diameter), color (light green, dark green), shelf life, seediness and nutritional quality. Cucumber breeders have combined several sex expression and fruit quality genes to develop desirable genotypes. Many pickling cucumber hybrids were developed by crossing gynoecious lines with monoecious lines. These hybrids are predominantly gynoecious in nature which provides pollens for fruit set which enhances total yield in pickling cucumber. Breeding technique for achieving these goals differ among breeders as does his/her definition of quality fruits. Gynoecious sex has also been combined with parthenocary trait to set fruit without pollen particularly for green house cultivation, since it eliminates the need for pollination and produces superior quality fruits. Gynoecious sex expression has been commercially exploited for the hybrid seed production since the female plants do not produce male flowers. Recently, the cucumber breeders have been interested in the development of carotene rich (yellow cucumber) lines. Several cucumber varieties have been developed for early characters, high yield, and resistance to diseases using heterosis breeding. The most commonly used breeding methods for the improvement of cucumber is inbreeding, single plant selection from segregating populations, heterosis breeding and presently marker assisted selection (MAS). The most common breeding procedure followed in cucumber is the selection from a local cultivar. Several F1 hybrids have been developed in cucumber both from public and private sector through hybridization across the globe. Cucumber is easily grown, indeterminate plant types, offer plenty of large flowers to work with over a long period of time where a large variation is observed for quantitative and qualitative characters. The use of gynoecious lines as one of the parent in breeding programme has made possible to enhance the area under hybrid cultivation. Recent QTL mapping and cloning studies in cucumbers for many quantitative traits will present a complete picture on the genetic architecture of these traits. The identification of molecular markers (SNPs and SSRs) for earliness, yield and quality traits would be directly useful in genome selection to expedite cucumber breeding in different market classes. The cloning of QTLs and genome wide association studies (GWAS) for important quantitative traits will be more innovative and future-focused for trait specific breeding of cucumber.
