The geographic distributions and complex genetic relationships among four Sorghum taxa identified in Taiwan

The genus Sorghum consists of 25 species, including Sorghum bicolor (L.) Moench, one of the top five cereal crops cultivated globally, and S. halepense, one of the most noxious weeds. Weedy Sorghum possesses outstanding adaptability and drought tolerance thrives in diverse environments and becomes an invasive plant worldwide. Taiwan is a unique place possessing suitable habitats for four Sorghum taxa, S. bicolor ssp. bicolor, var. technicum, ssp. verticilliflorum and S. halepense, which were identified by key morphological features. The four Sorghum taxa showed distinct geographic distributions, revealing that invasiveness was influenced by their own characteristics and human activities. The sporadic distributions of cultivated S. bicolor ssp. bicolor and var. technicum may be attributed to human disturbance and agricultural activities. The rhizomatous S. halepense was widely distributed and showed the highest genetic diversity (He > 0.776) among the four taxa, with its strong adaptation to various environments threatening the agricultural practices and ecosystem in Taiwan. In contrast, the newly naturalised S. bicolor ssp. verticilliflorum was confined to and dominant in southern Taiwan, with the lowest genetic diversity (He < 0.272). Significant genetic differentiation (F-ST = 0.5207) between the two ssp. verticilliflorum subpopulations was associated with natural geographic isolation. This study concretely elucidated the geographic distributions, genetic diversity and relatedness of invasive and escaped Sorghum taxa, indicating the potential aggressiveness and hazard of weedy Sorghum in Taiwan.