Screening Rice Genotypes for Weed Suppressive Ability Against Red Rice (Oryza punctata) in Costa Rica.

Red rice (Oryza punctata) is a problematic weed species for rice (Oryza sativa) producers in Costa Rica, often requiring labor intensive and financially restricting hand removal. Selecting rice genotypes for cultivar development that have inherent weed suppressive ability may provide producers with a cost-effective mechanism to control red rice. This study was conducted to screen available Costa Rican rice germplasm for weed suppressive ability through potential allelopathic expression. Twenty-two genotypes from the Costa Rican rice germplasm collection were screened in petri dishes to assess their ability to suppress the growth of two red rice populations collected from different regions of Costa Rica. Rice genotypes were arranged with individual red rice populations within each petri dish and red rice growth parameters were evaluated 10-d after establishment. Parameters collected include red rice germination, red rice root length, red rice shoot length, and red rice plant dry weight. Genotype affected root length of both red rice populations. The control treatment had the longest root length in both red rice populations and several genotypes provided for significantly shorter root length compared to the control. Genotype affected shoot length and plant dry weight for one red rice population but not the other. Results from these screens will guide subsequent breeding efforts focused on field screening rice genotypes for weed suppressive ability aganist red rice in Costa Rica.