Recent progress on the molecular breeding of Cucumis sativus L. in China

Molecular breeding of Cucumis sativus L. is based on traditional breeding techniques and modern biological breeding in China. There are opportunities for further breeding improvement by molecular design breeding and the automation of phenotyping technology using untapped sources of genetic diversity. Cucumber (Cucumis sativus L.) is an important vegetable cultivated worldwide. It bears fruits of light fragrance, and crisp texture with high nutrition. China is the largest producer and consumer of cucumber, accounting for 70% of the world's total production. With increasing consumption demand, the production of Cucurbitaceae crops has been increasing yearly. Thus, new cultivars that can produce high-quality cucumber with high yield and easy cultivation are in need. Conventional genetic breeding has played an essential role in cucumber cultivar innovation over the past decades. However, its progress is slow due to the long breeding period, and difficulty in selecting stable genetic characters or genotypes, prompting researchers to apply molecular biotechnologies in cucumber breeding. Here, we first summarize the achievements of conventional cucumber breeding such as crossing and mutagenesis, and then focus on the current status of molecular breeding of cucumber in China, including the progress and achievements on cucumber genomics, molecular mechanism underlying important agronomic traits, and also on the creation of high-quality multi-resistant germplasm resources, new variety breeding and ecological breeding. Future development trends and prospects of cucumber molecular breeding in China are also discussed.