Collectotrichum gloeosporioides is a highly aggressive fungi species causing diseases in plants throughout the world. In Bangladesh, C. gloeosporioides has been reported to have caused leaf blight disease of Dalbergia sissoo in 2021. Seeds and seedlings of D. sissoo were examined in vitro for their susceptibility to C. gloeosporioides and other two Colletotrichum species, namely C. fragariae and C. siamense. Mycelial agar plugs and spore suspension of the Colletotrichum species were used to inoculate seeds and seedlings of D. sissoo. Susceptibility was measured in terms of pathogen virulence to inoculated seeds and seedlings and data were recorded after 14 and 42 days of observation, respectively. The findings of the study showed that the germination percentage of the inoculated seeds decreased more by C. siamense (45-54%) as compared to C. fragariae (33-49%) and C. gloeosporiodes (45-51%). On the other hand, the mortality rate (%) increased by C. fragariae (~43%) as compared to C. siamense (35%) and C. gloeosporioides (33%). The results revealed that seeds and seedlings of D. sissoo are at risk of infection by C. gloeosporioides. In addition, non-host pathogens such as C. fragariae and C. simense may also pose a serious threat to seeds and seedlings of D. sissoo. This is an important concern regarding the natural regeneration of the tree species in the areas of Bangladesh facing disease.