Weedy rice (Oryza sativa f. spontanea) is an annual, undesirable plant and is known to have a relationship with cultivated rice. Weedy rice is considered one of the threatening weeds due to its similarity of morphology with rice, high competitiveness leading to reduced rice yield and quality, reduced effectiveness of control measures and increased production cost. Similar to cultivated rice, weedy rice is very diverse in morphology and occurs in all major rice-growing regions of the world, such as Asia, America, Africa and Europe. In Vietnam, weedy rice was first recorded in the early 1990s in some dry-sowing rice areas of Long An and Binh Thuan provinces, with morphological characteristics such as taller than cultivated rice, long awn, red rice grain, and very easy shattering. To date, according to unofficial data, weedy rice is present in all rice-growing provinces and different rice farming systems. This research focuses on collecting, observing, and analyzing morphological characteristics of weedy rice lines collected from some major ricegrowing ecological regions in the Mekong delta including Can Tho, Hau Giang and Kien Giang. Nineteen morphological features were collected, recorded and analized using principal component analysis (PCA) and hierarchical clustering (HC). The results of initial observation and analysis of 248 collected weedy rice samples and 3 widely cultivated rice varieties show that weedy rice is very diverse in morphology and there are 28 weedy rice lines with distinct morphological characteristics. Principal component analysis of 28 weedy rice lines and 3 cultivated rice varieties showed that a total of 47.5% of the variation was explained by several major variables, such as rice grain length, grain color, and awn length. The hierarchical clustering classification of 31 samples resulted in 4 main groups, of which 2 weedy rice lines within the same group had similar features to cultivated rice varieties, namely LCHG-49 and LCHG-56.
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