Abstract

Weed competition is a major constraint in rice production systems in Africa. This study was conducted at the Africa Rice Experimental Station in Benin in the dry and rainy seasons to screen rice varieties for weed competitiveness. The experimental design was a split plot with 14 contrasting cultivars (including the Oryza glaberrima and Oryza sativa parents of upland New Rice for Africa (NERICA), lowland NERICA or “promising lines”) planted under three weeding regimes: 0, 1 and 4 weedings. Agro-morphological characters, growth indexes and weeds were used to evaluate the cultivars. The most important weed species encountered were Acanthospermum hispidum, Dactyloctenium aegyptium and Digitaria horizontalis. Highly significant differences (P£0.0001) between cultivars were observed in weed biomass. The impact of weeds on agro-morphological traits was expressed through an increasing senescence of plants in relation to the weeding regime. Weed-competitive cultivars typically showed a leaf area index less than 3, a high specific leaf area and a Soil-Plant Analyses Development (SPAD) unit less than 30. High affinities between traits were observed and three types of descriptors were identified based on their broad sense heritability. CG20, an O. glaberrima variety was the most competitive against weeds.

Key words: Rice, descriptor, weed, competitive variety, heritability.