A study on competitive ability of rice yellow mottle virus resistant and non-resistant rice cultivars with wild rice species

Introduction of Genetically Modified (GM) rice cultivars resistant to diseases such as RYMV is one of the feasible options to stabilize rice production in disease hotspots area. However, the need to assess in terms of risks associated with their introduction in the country like Tanzania is mandatory by the EMA 2004. This study used a simulated approach of the introduced GM cultivars to assess their competitive ability with wild species using locally developed cultivars. The study aimed to generate the important scientific information on the simulated competitiveness of GM cultivars resistant to RYMV rice cultivars as compared to susceptible cultivar with wild rice species. Field experiments were conducted at KATRIN in Kilombero Valley and at Dakawa Research Center (DRC) in Mkata Alluvial Plains. Both sites are in Morogoro region. At KATRIN site two cultivars (TXD 85-nonresistant and Gigante-resistant to RYMV) and a wild species -O.longistaminata were used, whereas at DRC, TXD85, Tog 5681- resistant and a wild species- O puntata were used. The cultivars were planted in mixed and monocultures at both sites. In monoculture the standard spacing of 20cm x 20cm was used while in mixed culture the spacing varied with plant population densities of each rice species. Data of grain yield components, pltuit growth parameters, and biomass and growth patterns were collected. The analysis was performed using the two way ANOVA. Separation of means was done by using Duncan Multiple Range Test. Rice species showed no significant differences for the dry weights, except in the monoculture at Dakawa. The wild species flowered and matured earliest in both pure and mixed stands than the cultivated species. The non- resistant cultivar had higher grain yield components. The wild species had the lowest tiller number and scored the tallest height than cultivated rice in both the pure and mixed stands at all growth stages at both sites. The wild species therefore were the best competitors in mixed cultures than the RYMV resistant and non-resistant cultivars. The resistant cultivars were the better competitors in mixed than the non-resistant cultivar. The study has paved the way for ecological risk assessment studies, and breeding of rice cultivars with combined competitive ability and RYMV resistance is recommended.