Accelerated cassava varietal turnover in Tanzania, a direct result of cassava seed system interventions

Jessey Anderson Msami ^1* Mathias Ndalahwa ¹ Jonas Nickas ¹ Maria Arbogast ² James Nkwabi ² Nsajigwa Mwakyusa ² Ambilikile Mwenisongole ² Dwasi Gambo ² Lava Kumar ³ James Legg ^1*

• ¹ International Institute of Tropical Agriculture (Tanzania), East African hub, Tanzania
• ² Tanzania Agricultural Research Institute (TARI), Dodoma, Dodoma, Tanzania
• ³ International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria

Cassava is a vital food security crop grown in the tropics primarily for its starchy tuberous roots that play a significant role in calorie intake in Africa. The cassava seed system has been historically neglected resulting in the widespread propagation of poor quality and diseased planting materials (stems/cuttings). Recently there have been ongoing efforts to modernise cassava breeding and improve seed delivery in Tanzania which have resulted in the creation of a functional and commercially sustainable cassava seed system. This system comprises a decentralized network of seed producers in a hierarchy from early generation to community-based seed with different quality assurance requirements at each level. Seed entrepreneurs are registered on a 'SeedTracker™' database (www.seedtracker.org) where volumes of seed produced can be tracked for each variety. In this study, we analysed SeedTracker™ data and household survey data to determine the Weighted Average Varietal Age (WAVA) of improved cassava varieties in Tanzania. We followed the approach of Brennan and Byerlee (1991) and used total seed (cuttings) produced as weights for WAVA estimations. Results showed changes in WAVA in the past six years from 15.2 years in 2018 to 12.0 years in 2023, which is a significant decrease. This suggests that there is an accelerating turnover rate of improved cassava varieties. The findings of this study are useful to cassava seed system actors such as policymakers, quality assurance agencies, breeders, and seed businesses. This study also serves as an indicator of the positive impacts being achieved through cassava seed system interventions in the country. Furthermore, it validates the adopted cassava seed system model and suggests that the model could be readily adapted to other crop systems where varieties are being routinely monitored.