**3.2 Breeding methods**

Several breeding methods have been employed for the genetic improvement of cucumber depending on the specific breeding objectives. Single plant selection, single seed descent method, mass selection, simple backcross breeding, pedigree selection, hybridization, use of sex inheritance and chemicals in breeding, and population improvement and extraction of inbred lines are the most common methods used. In recent time, marker assisted selection derived lines have been developed for the improvement of quantitative and qualitative traits in different cucumber market classes. Simple backcross breeding is quite useful for transferring characters governed by single genes e.g. disease resistance or quality traits from donor lines to more stable recurrent parents. Often, six generations of selection and backcrossing to the recurrent parent are required to recover the desired genotypes (recurrent parent + additional trait). Single seed descent method is useful for the development of inbred lines by self pollination. In chemical breeding the gynoecious lines are treated with Silver nitrate/silver thiosulphate to induce hermaphrodite flowers for pollination. The population improvement method is based on recurrent selection and aims at long term gains for the characters having low to moderate heritability. The exploitation of hybrid vigor in cucumber is desirable due to high heterosis for earliness, yield and disease resistance. Heterosis breeding can exploit the genetic diversity present in cucumber for various growth and yield characters. In Western countries almost 90% of the area of cucumber is under F1 hybrids.
