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Weedy rice can severely impact rice production through yield reduction because of its competitive ability to reduce growth resources for cultivated rice. The characteristic weedy traits have made weedy rice very challenging to manage as they have the same agro-morphological characteristics with cultivated rice. The study examined the relationships between selected cultivated rice (Oryza sativa L.) cultivars, weedy rice biotypes, and wild rice collected from different locations in the Philippines, using simple sequence repeat markers. Cluster analysis, using UPGMA, enabled the genetic differentiation and relationships examination of the test materials. Subgroups of 13 with at least two biotypes formed 100% similarity based on post-harvest data, with the cultivated rice cultivars forming one subgroup. With polymorphic SSR markers, five major clusters range from three (group I) to 62 biotypes (group III). There was 100% similarity observed for 15 subgroups ranging from two to 10 biotypes. The wild rice cultivars formed species-specific groupings. Subgroups with 100% similarity came from the same province; likewise, one with 100% similarity came from both Iloilo and Batangas; and still another from cultivated rice cultivar and weedy rice biotype from Pangasinan. The possible relationships of weedy rice biotypes with wild rice relatives (>65% similarity) include two biotypes related to Oryza minuta, one for O. meyeriana, and 22 biotypes for O. rufipogon. Concerning cultivated rice cultivars, high similarity (>80%) was observed in 22 biotypes closely related to PSB Rc 82, 13 biotypes to NSIC Rc 222, six to NSIC Rc 160, three biotypes each to NSIC Rc 215, NSIC Rc 152, NSIC Rc 64, NSIC Rc 18, and NSIC Rc 10, and one biotype each to IR64 and NSIC Rc 14. [ABSTRACT FROM AUTHOR]