Author(s): Hongxiang Zhang 1, Fan Wu 1, Wenli Guo 1, Rong Bai 1, Zhuanzhuan Yan 1, Blaise Pascal Muvunyi 1, Qi Yan 1, Yufei Zhang 1, Xianfeng Yi 2,*, Jiyu Zhang 1,*
The genus Melilotus (sweet clover) consists of 19 annual and biennial species and belongs to the tribe Trifolieae of the legume family. Almost all species are native to North Africa or Eurasia, and manys can be found in North of China and Central Asia [1,2]. Melilotus is an important forage crop, and certain species, such as M . albus , M . officinalis and M . indicus have been cultivated in many regions . Compared with other forages, the members of Melilotus can tolerate extreme environmental conditions, such as drought, cold, and high salinity [1,4], and its nitrogen fixation rate is higher than that of other legumes, which can increase soil fertility . Additionally, Melilotus is valuable because of its coumarin content, and thus represents a possible medicinal plant resource. Due to its affordability and abundance as well as its potential market value, Melilotus is worthy of further investigation .
Genetic diversity within a particular species helps plants adapt to various environmental conditions, such as fluctuating climate and soil conditions; thus, assessing the diversity of available plant genetic resources is necessary to identify the genes associated with useful biological functions that can then be rationally integrated to design new varieties . Plant genetic diversity has gained increasing attention because of the increase in human population as evidenced by rapid urbanization and the conversion of cultivable lands. These are the critical factors contributing to food insecurity in the developing world . Consequently, the Consultative Group for International Agricultural Researches has begun establishing research centres and gene banks to conserve the plant genetic resources of staple food crops around the world, such as maize from Mexico, rice from North China and potatoes from Peru (for more information, see http://www.cigar.org/center/index.html).) The purpose of this organization is to maintain genetic diversity and to provide tools for population monitoring and assessment that can be used for conservation planning . Forage crops also play an increasing role in farming system with the emphasis on development of sustainable agricultural production and the researches about genetic diversity on forage will assume greater importance for germplasm collections and breeding work [10,11]. Genetic diversity assessments are performed using morphological, biochemical and DNA marker analyses. Based on further studies on biological resources, improvements of molecular biology technology, the maturation of amplification and sequencing technologies, and decreases in costs, DNA markers have become the primary method of analysing genetic diversity. Currently, a wide range of DNA markers have been employed to assess genetic diversity, and these include random amplified polymorphic DNA (RAPD) has been adopted in bamboo , restriction fragment length polymorphisms (RFLPs) in rice , amplified fragment length polymorphisms (AFLPs) in walnuts , simple sequence repeats (SSRs) in potato , single nucleotide polymorphisms (SNPs) in wheat , and chloroplast DNA (cpDNA) in Brassica napus [17,18].
A previous study showed that the leaves, flower...