Wheat(Triticum aestivum L.) is one of the world’s foremost food crops, providing a staple food source for more than half the world’s human population (Röder et al., 1998). Volunteer wheat is an emerging form of wheat with weed characteristics that is widely distributed in all the major wheat-planting areas and the frequency of volunteer wheat is 50.3%-92.1% (Su et al., 2021a). It is a self-pollinating species with 42 chromosomes, the same as cultivated wheat(Fan et al., 2010), so volunteer wheat is also referred to as “wild wheat” or “semi-wheat”. The plant height of volunteer wheat was 30.0%~135.7% higher than that of cultivated wheat, the ear length was smaller than that of cultivated wheat, the number of grain number per spike was less than that of cultivated wheat, the thousand-grain weight was 22.6%~42.4% lower than that of cultivated wheat, and the stem diameter was significantly smaller than that of cultivated wheat(Su et al., 2021a). In addition, volunteer wheat is a species of wheat with aggressive tillering, rapid growth, and effective seed dispersal and could be widely used for modern wheat breeding (Fan et al., 2010). The endogenous abscisic acid content of the long-dormant volunteer wheat seeds was significantly higher than that of the short-dormant material, which enabled them to remain dormant in the field without germination and naturally over-summer, making it very easy to mix with cultivated wheat(Su et al., 2022).
The infestation of volunteer wheat has already caused serious damage to cultivated wheat by competing for water, fertilizer, sunlight and other resources, resulting in significant reductions in wheat yield (Shivrain et al., 2010; Su et al., 2021b). The photosynthetic characteristics, chlorophyll fluorescence parameters, pigment content and malondialdehyde content of volunteer wheat were higher than those of cultivated wheat(Sun et al., 2021). In addition, it is a particularly troublesome weed due to similarities to cultivated wheat, making it extraordinarily difficult to control with herbicides or other methods (Gealy et al., 2002). Furthermore, there are various types of volunteer wheats, with different morphologies and possibly different origins (Kane et al., 2007; Su et al., 2021a). However the moisture content, protein content, wet gluten content, water absorption, softening degree and extensibility of volunteer wheat were higher than those of cultivated wheat(Su et al., 2021b). Although there have been some studies of the genetic diversity of volunteer wheat, the genetic relationship of volunteer wheat still remains controversial. Consequently, it is necessary to clarify the genetic diversity of volunteer wheat in order to provide effective control and utilization.
Since the late 1980s, wheat breeders and geneticists have identified and used DNA molecular markers including sequence characterized amplified regions (SCAR), single nucleotide polymorphisms (SNPs), inter simple sequence repeats (ISSRs), and SSRs to improve wheat breeding and quality (Ali et al., 2019). Most reported studies have been carried out on the genetic diversity, genetic mapping, population structure and phylogenetic relationship of barley(Hordeum vulgare L.)(Wang et al., 2014; Liu et al., 2011; Lai et al., 2016; He et al., 2013), spring wheat (Wang et al., 2013), wheat (Zhao et al., 2009), and winter wheat (Li et al., 2014). SSR markers have been widely used to study genetic mapping, genetic diversity, resistance identification, marker-assisted selection and parental analysis (Ali et al., 2019) of food crops including wheat (Prasad et al., 2000), maize (Zea mays Linn. Sp.) (Wang et al., 2014), soybean [Glycine max (L.) Merr. ] (Zhang et al., 2014), potato (Solanum tuberosum L.) (Liao et al., 2014), and weedy rice (Oryza Satiua L.) (Shao et al., 2011; Li et al., 2018). SSR primer pairs are considered the most useful marker for plant breeding and plant genetics, because of their co-dominant, multi-allelic nature, and relative abundance with an excellent genome coverage (Ali et al., 2019; Aitken et al., 2005). Ivandic et al. (2002) used 33 SSR markers to analyze the genetic diversity of 39 wild barley genotypes from Israel, Turkey and Iran, showing that most of the materials could be classified by country. Fu et al. (2007) used SSR markers to analyze 47 wheat varieties in Sichuan, China and found that the genetic background of the selected materials was very similar.
At present, there are three methods used to detect SSR marker fragments: agarose gel electrophoresis (AGE), natured and denatured polyacrylamide gel electrophoresis (PAGE), and microchip capillary electrophoresis (MCE). MCE is a useful tool that is widely applied to the management and analysis of plant genetic resources (Piergiovanni and Angela, 2013). It is rather faster, more accurate and more efficient than the other two detection methods. MCE also has the advantages of only requiring small quantities of reagents and samples, so that microfluidic instrumentation can achieve efficient separation of molecular species (Minucci et al., 2014; Revermann, 2007).
Germplasm resources are the material basis of breeding, while accurate analysis and evaluation of germplasm resources is the premise of rational utilization of resources, thus it is necessary to fully understand the degree of genetic variation of breeding materials. There is little information on the genetic relationship and molecular identification of volunteer wheat, and thus a complete system and set of evaluation criteria have not been developed. To better understand the genetic relationship of these cultivated wheat and volunteer wheat strains, this study aimed to characterize the genetic diversity and population structure of 224 samples by MCE technology. It is hoped that it is of great significance to reveal the genetic diversity between the volunteer wheat and the cultivated wheat population as well as within the population, to understand its genetic background, and to further the comprehensive management strategy and utilization of gene resources of associated wheat.