Weed-suppressing rice cultivars - does allelopathy play a role?

A range of 111 rice cultivars was studied for weed-suppressing ability in f ield experiments with a sown infestation of Echinochloa crus-galli. Cultiva rs differed significantly in their ability to suppress the growth of E. cru s-galli, and the differences were reasonably reproducible over three season s. The same rice cultivars were tested in a laboratory screening for allelo pathic potential, which showed significant differences in the ability to re duce root growth of E. crus-galli. Correlation between the laboratory scree ning and the field experiments showed that field performance could be descr ibed to some extent by E. crus-galli root length reduction in the laborator y. Plant height in the field experiment was correlated with weed biomass 8 weeks after seeding. Even among the most weed-suppressing rice cultivars, h owever, all heights were represented. None of the measured growth parameter s from greenhouse studies could explain the distribution of weed-suppressin g rice cultivars. This indicates that allelopathy in combination with compe titive ability determines the weed interference outcome of a given rice cul tivar.