Salient characters of Weedy rice (Oryza sativa f. spontanea) populations in highly infested areas in Sri Lanka

Weedy rice (WR) was first reported in 1990 and it is occurring with varying population densities in all agro-ecological zones in Sri Lanka. The identification of WR eco-types using agro-morphological characters which vary with time and remains as a major problem among the farmers and the agronomists. The WR population possesses a number of pleisomorphic (primitive) and apomorphic (derived) characters. This study focuses on identification of primitive and derived characters observed in WR. The identification of the salient trends of specialization of characters in WR populations facilitates the understanding of the rate diversification of WR populations. Seeds of presumed WR eco-types were collected from five different locations in Kurunegala and Matara districts. Five replicates with three plants of each eco-type were planted in plastic pots with representative paddy soils from each location. Replicates were arranged in Complete Randomized Design (CRD). Agro-morphological characterization (using thirty characters) of WR eco-types, wild rice and cultivated rice varieties were made using a Standard Characterization Catalogue. The collected data were separated into nominal and scalar variables and the nominal data were used to construct Classification and Regression Trees using CART algorithm. The long-fully awned and absence of awn were pleisomorphic characters and short-fully awned and long-partly awned characters were apomorphic in WR eco-type populations in Sri Lanka. These characters could be hypothesized as derived from mixing of germplasm either of cultivated or wild rice varieties indicating the possibilities of cross-pollination among wild, cultivated and weedy rice eco-types.

Ruhuna Journal of Science Vol.5 2014; 31-36