Path analysis of two sympatric weed species (Echinochloa crus-galli ssp. crus-galli (L.) Beauv. and Ischaemum rugosum Salisb.) in competition with rice (Oryza sativa L. var. MR84) - a comparative study.
Baki B. BakarA, Lajili Nabi Ahmed NabiA, Suhaimi SaadA, Suzana Abdul AzizA and Abdul Munir JaafarB
A Institute of Biological Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia.
B Statistical Unit, Malaysian Agricultural Research and Development Institute, GPO Box 12301, 50744 Kuala Lumpur, Malaysia.
Summary
The impact of weed and crop density on the yield components of rice is central to an understanding of the way weed competition influences yield potential of rice. Path analysis has been used quite intensively in agronomy, ecology and, of late, in weed science. In order to evaluate the differential competitive ability of two sympatric weed species (Echinochloa crus-galli ssp. crus-galli (L.) Beauv. and Ischaemum rugosum Salisb.) with rice (Oryza sativa L. var. MR84) and the causal relationships between grain yield components using path analysis, a series of experiments was conducted in an insect-proof house at the University of Malaya, Kuala Lumpur in 2000-2002. The analysis quantified direct effects of the two weed species and MR84 rice densities on the yield components (grain weights, numbers of filled and unfilled grains, number of grain per panicle, panicles per plant and number of reproductive and non-reproductive tillers) of MR84 and the two weed species.
The path analysis model illustrated the direct and indirect effects of the components of yield on fecundity and grain yield per plant. The direct effects of MR84 and the two weed species densities on the number of panicle per plant and the number of seeds per plant were always positive. In contrast, the effects of density on the number of tillers per plant, grain weight per plant, per cent filled panicles per plant varied from positive to negative reflecting the inconsistent and unequal influence of density-dependent factors. The analysis indicated that the number of tillers per plant and the number of panicles per plant were the key yield components determining the response of fecundity and grain yield to crop-weed competitions.Plants of E. crus-galli ssp. crus-galli and I. rugosum competing with the rice crop registered significant differences in path coefficients for each yield component recorded, thereby reflecting the differential competitive ability of the two weed species against the rice crop.
Plant Protection Quarterly (2005) 20 (2) 67-73.