Growth traits of diverse rice cultivars under severe competition: implications for screening for competitiveness

Abstract

Over 30 root and shoot growth traits of nine diverse rice cultivars (cvs) grown under competitive conditions were analyzed to exhaustively quantify cv differences and identify which traits most affected rice growth in competition. The cvs included a traditional Oryza glaberrima, CG14, and selections from three isozyme groups of O. sativa: aus, indica, and tropical japonica. Single rice plants were grown in pots with and without nitrogen fertilizer, surrounded by six plants of either barnyardgrass ( Echinochloa crus- galli), in trials 1 and 2, or themselves, in trial 3. Growth traits were measured weekly or in harvests at 21 and 48 days after seeding (DAS). Significant differences amongst cvs were found for nearly every response variable, and the most productive cvs lacked uniform growth traits. Total dry mass (DM) was primarily a function of leaf area (LA, m −2 per plant), but height growth rates (HGRs, m per day) at 7 and 21 DAS and tillering ability were also consistently important. Non-destructively measured traits, such as tillering, and HGRs at 7 and 21 DAS, accounted for at least 75% of the variation in DM across all trials. Overall, rice cv growth in competition depended on multiple traits, and in particular was not simply a function of specific leaf area (SLA, m 2 g −1 leaf). Early vigor was highly repeatable in both competition and monoculture trials, indicating that it may be used to discriminate between more and less competitive cvs even in monoculture. Therefore, screening lines in standard nurseries for competitiveness against weeds seems possible using non-destructive scoring of plant cover, very early heights (i.e., vigor), tillering ability, and early HGRs.