Weed‐suppressing rice cultivars – does allelopathy play a role?

A range of 111 rice cultivars was studied for weed‐suppressing ability in field experiments with a sown infestation of Echinochloa crus‐galli. Cultivars differed significantly in their ability to suppress the growth of E. crus‐galli , and the differences were reasonably reproducible over three seasons. The same rice cultivars were tested in a laboratory screening for allelopathic potential, which showed significant differences in the ability to reduce root growth of E. crus‐galli . Correlation between the laboratory screening and the field experiments showed that field performance could be described to some extent by E. crus‐galli root length reduction in the laboratory. Plant height in the field experiment was correlated with weed biomass 8 weeks after seeding. Even among the most weed‐suppressing rice cultivars, however, all heights were represented. None of the measured growth parameters from greenhouse studies could explain the distribution of weed‐suppressing rice cultivars. This indicates that allelopathy in combination with competitive ability determines the weed interference outcome of a given rice cultivar.