## 4 Discussion  
To date, a variety of DNA markers have been widely used in crops for germplasm evaluation, DNA fingerprinting, genetic diversity analysis, genetic mapping, and QTL mapping. Single-nucleotide polymorphisms (SNPs) based on the genomic sequence of varieties, together with SSRs, are suitable molecular markers for DNA fingerprinting and improving the precision of variety differentiation, as proven by previous reports. However, compared with SNPs, SSRs are the better choice for DNA fingerprinting and genetic diversity studies due to their low cost, reliability, and allelic diversity [22]. In recent decades, SSR markers have been widely used in field and horticultural crops [6; 23]. In this study, 21 pairs of SSR markers differentiated 10 broccoli genotypes with 100% polymorphic loci, indicating that SSR markers are an effective molecular marker type for DNA fingerprinting and genetic diversity.  
In previous reports, most studies of DNA fingerprinting based on SSRs or SNPs focus mainly on cultivar crops; as a result, these polymorphic markers are usually only used in genetic diversity or DNA fingerprinting among intraspecific cultivars or interspecific plants. In this study, a few core SSRs (LTSSR13) could be used to identify interspecific and intergenic hybrids in homozyggotes or resources in genetic diversity, as well as _Brassica oleracea_ and _Brassica napus_ crops, which is a new approach for distinguishing _Brassica_ plants in identifying homozyggotes.  
Quick response (QR) codes have been widely used in mobile applications due to their convenience and the pervasive built-in cameras on smartphones. In this study, we proposed ScreenID to enhance QR code security by identifying its authenticity, which embeds a QR code with information from a unique screen DNA fingerprint of broccoli with CR genes. This study provided a model for the interaction between the camera and screen in the temporal and spatial domains. More extensive experiments have demonstrated that ScreenID can efficiently differentiate screens of different models, species and manufacturers and thus improve the security of QR codes [24].  
The clubroot disease resistance genes of cruciferous vegetables are mainly from turnip, radish, rapeseed, and Chinese cabbage [25; 26], and most of these resistance materials usually contain a single CR gene, which may cause serious weakening and increasing the planting risk. In the future breeding, the varieties with resistance to multiple physiological races could fundamentally solve the problem of clubroot on crucifers. In this study, 10 disease-resistant _Brassica_ plants aggregating five or more clubroot resistance genes were finally obtained, and these important materials might help us to accelerate the development of breeding for broccoli and the other _Brassica_ crops resistant to multiple physiological races.  
From this study, another achievement is assessing the genetic diversity of 10 broccoli genotypes. These 10 broccoli resources were divided into three distinct groups, indicating that high genetic variation was present in broccoli carrying multiple CR genes, which was first announced in previous studies [17; 27]. In particular, our study provided more information on the genetic diversity of _Brassica oleracea_ crosses with _Brassica napus_ and turnip than cultivars [28]. This study also showed that the genetic diversity of 10 broccoli resources was relatively large, with genetic similarity coefficients ranging from 0.57 to 0.91, which has broadened the genetic variation in broccoli, _Brassica napus_, and turnip generations in cross-breeding programs [1]. Moreover, more generations should be improved and purified, as well as further research on the molecular mechanism of domain genes, serving for broccoli breeding and other _Brassica_ crops, in disease resistance, stress resistance, and high quality [17].