Cucumis sativus: Chromosome evolution, domestication, and genetic diversity: Implications for cucumber breeding

Authors: Weng, Yiqun

Submitted to: Plant Breeding Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2020
Publication Date: 11/13/2020
Citation: Weng, Y. 2021. Cucumis sativus: Chromosome evolution, domestication, and genetic diversity: Implications for cucumber breeding. In: Goldman, I., editor. Plant Breeding Reviews, Volume 44. Wiley Online Library. p. 79-111. https://doi.org/10.1002/9781119717003.ch4.
DOI: https://doi.org/10.1002/9781119717003.ch4

Interpretive Summary: WHY: Cucumber is an economically important specialty crop, and a favorite model for study of several important biological phenomena in plants. However, little is known about the history on how cucumber was evolved through evolution and domestication to result in what we see today. WHAT: I reviewed the literature on our knowledge on the following fields. 1) Where did the 14 chromosomes come from? 2) What happened during cucumber domestication? 3) How human selection/breeding shaped the different cucumber market classes? 4) What we can learn from the knowledge for cucumber improvement? IMPACT STATEMENT 1. This review provides the state-of-the-art in this, which is helpful for cucumber researchers and evolutionary biologists. 2. This review also provides useful information for efficient use of cucumber crop wild relatives, and exploration of the genetic diversity in collections for cucumber breeding.

Technical Abstract: Cucumber, Cucumis sativus L. is an important vegetable crop worldwide. Among the ~66 species in Cucumis, cucumber is the only one with 2n = 2x = 14 chromosomes, and the rest, including its sister species, C. hystrix, have 2n = 2x = 24 chromosomes or its multiples. Cucumber was evolved from its extinct 2n = 24 ancestor through dysploid chromosome reduction, in which many chromosome rearrangement events (inversions, fusions and translocations) were involved with the exception of cucumber Chromosome 7 which remained largely intact during the entire evolution of Cucumis. There are four cross-compatible botanical varieties in C. sativus including the wild cucumber (C. s. var. hardwickii), the semi-wild Xishuangbanna cucumber (C. s. var. xishuangbannesis), the Sikkim cucumber (C.s. var. sikkimensis), and the cultivated cucumber (C.s. var. sativus). The wild cucumber is the progenitor of cultivated cucumber, but differentiated from the rest three taxa in the amount and distribution of heterochromatins, as well as six large inversions. Cucumber has been cultivated in India for at least 3,000 years, which spread eastward to China and westward to Europe around 2,000, and 700–1500 years ago, respectively. Long-term selection and breeding practices have resulted in different ecotypes and market classes of cucumber adapting to local environments, production systems, processing requirements, as well as consumer needs. Recent molecular marker studies have provided more insights into the population structure and genetic diversity on worldwide cucumber collection. The knowledge on cucumber evolution, domestication and genetic diversity will greatly help the conservation of genetic diversity, and efficient use of cucumber germplasm resources for cucumber improvement.