Growth Variability of Italian Weedy Rice Populations Grown with or without Cultivated Rice

Weedy rice (Oryza sativa L.) exhibits a great variability of morphological traits. To detect if this variability can affect its growth behavior, two experiments were performed on 10 Italian weedy rice populations grown as pure stand and in competition with rice. Five awnless and five awned populations were grown in field conditions in 15-L pots. In the pure stand experiment, each pot hosted a single plant of weedy rice, while in the competition experiment the weedy rice plant was surrounded by 10 plants of cultivar Sirio CL. Plant height, tiller, and leaf numbers were recorded six times during the growing season. In competition, leaf area, culm weight, and leaf weight were also assessed. In pure stand, no significant differences between awned and awnless groups were found for all the considered parameters. Differences were found in plant height (from 70.7 to 91.9 cm) and leaf weight (from 5.64 to 9.85 g plant(-1)) among awned populations only. In competition, weedy rice showed lower and more variable growth indices. The least and most affected growth variables were plant height (16% of average reduction in comparison with pure stand) and leaf weight (70.3% of average reduction), respectively. Awned populations showed higher and more variable values of growth parameters, suggesting a stronger competitiveness and a wider phenotypic plasticity. Knowledge of growth behavior related to weedy rice variability could improve modeling of infestation dynamics and highlights the need of an integrated weed management approach.