Job’s tears (Coix lachryma-jobi L.) is an important crop used as food and herbal medicine in Asian countries. A drug made of Job’s tears seed oil has been clinically applied to treat multiple cancers. In this study, the genetic diversity of Job’s tears accessions and the fatty acid composition, triglyceride composition, and anti-proliferative effect of Job’s tears seed oil were analyzed using morphological characteristics and ISSR markers, GC-MS, HPLC-ELSD, and the MTT method. ISSR analysis demonstrated low genetic diversity of Job’s tears at the species level (h = 0.21, I = 0.33) and the accession level (h = 0.07, I = 0.10), and strong genetic differentiation (GST = 0.6702) among all accessions. It also clustered the 11 accessions into three cultivated clades corresponding with geographical locations and two evidently divergent wild clades. The grouping patterns based on morphological characteristics and chemical profiles were in accordance with those clustered by ISSR analysis. Significant differences in morphological characteristics, fatty acid composition, triglyceride composition, and inhibition rates of seed oil were detected among different accessions, which showed a highly significant positive correlation with genetic variation. These results suggest that the seed morphological characteristics, fatty acid composition, and triglyceride composition may be mainly attributed to genetic factors. The proportion of palmitic acid and linoleic acid to oleic acid displayed a highly significant positive correlation with the inhibition rates of Job’s tears seed oil for T24 cells, and thus can be an important indicator for quality control for Job’s tears.

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Job’s tears (Coix lacryma-jobi L.) is an ancient plant with high nutritional and medicinal values. In this study, using 11 Job’s tears germplasm resources collected throughout China, we examined genetic differences among germplasms and differences in the in vitro antioxidant activities of coixan and sought to identify inter-relationships between these two variables. We found that the intraspecific conservation of DNA sequences was high, with ITS regions and cpDNA trnL-F and trnH-psbA non-coding sequences showing no sequence variation, whereas the GBSSI gene showed a certain degree of variation among the different Job’s tears germplasms. EST-SSR analysis also revealed a relatively low level of genetic diversity among germplasms. Coixan was shown to be an efficient antioxidant, and among the germplasms examined, the LNYX, FJPC and AHBZ had the highest antioxidant activities. However, none of the four in vitro antioxidant activity indices we assessed were significantly correlated with the geographical origin of the germplasm (latitude and longitude), and one of them had significantly associated with genetic diversity. Although the factors affecting the antioxidant activity of coixan are complex, the role of heredity should not be ignored. Our findings have implications for the scientific evaluation, identification and sustainable utilization of Job’s tears germplasm resources.