Low temperature seriously constrains the adoption of high-yielding varieties in high-elevation and subtropical regions of Africa. Cold can occur in both the rainy and dry seasons, damaging leaf tissues and causing spikelet abortion. Cold tolerance would allow farmers to grow rice in mountainous regions and would facilitate double cropping in some lowland areas. Improved indica and japonica breeding lines are already available that are known to possess cold tolerance, during both the seedling and reproductive stage. Introducing cold-tolerant varieties into Africa would have an immediate impact in areas of persistent poverty.
THE STRASA SOLUTION
Thirty-six (36) BC3F6 lines were screened for yield in Senegal after confirming their cold tolerance at seedling stage. Superior lines will be nominated to the Africa Rice Breeding Task Force (ARBTF) 2019 MET for screening in irrigated lowlands. Thirty (30) multiple stress-tolerant lines with good grain quality have been distributed to Ethiopia, Madagascar, and Rwanda for evaluation at high elevation sites through the ARBTF network. Another 50 fixed cold-tolerant lines have been identified for future MET trials in these countries. In the irrigated lowlands, 36 lines were distributed for evaluation in 21 sites through the ARBTF network, including NARS sites in Burkina Faso, Madagascar, Mali, Mozambique, Nigeria, Senegal, and Uganda, at AfricaRice trial sites in Mbe, Cote d'Ivoire, Ndiaye, Senegal, Ibadan, and Nigeria, and at the IRRI ESA site in Burundi.
Line development: A field-based RGA through SSD was established by the AfricaRice Irrigated Lowland Breeding Unit in Senegal and also by the AfricaRice High Elevation Breeding Unit in Madagascar. In Senegal, 157 fixed breeding lines were screened for seedling stage cold tolerance during the 2018 DS and 77 tolerant lines were identified. These cold-tolerant lines have been advanced and screened in yield trials during the 2018 WS in Ndiaye and Fanaye. Analysis of the yield data from the two sites revealed significant GxE interaction. In Madagascar, breeding lines from populations derived from crosses between WAB 189 and X-Jigna with Chomrong Dhan, a highly cold-tolerant variety which is well-adapted to Madagascar highlands, were screened and highly cold-tolerant lines were identified. Separately, three lines superior in performance over local checks were identified after screening 48 lines in Antsirabe under combined effects of cold and flooding (3-7 days flooding at an average temperature of 15°C) over a period of 30 days.
Stress mapping and upgrading screening facilities
Cold storage rooms at the AfricaRice sites in Madagascar and Senegal were renovated and data loggers were installed at trial sites in Madagascar and Rwanda for the monitoring of air and water temperatures. Improved phenotyping protocols were distributed to NARES partners in Mali, Rwanda, Madagascar, Ethiopia, and Senegal.
Inventory of existing cold-tolerant germplasm completed and screening protocol developed
A total of 170 cold-tolerant lines were identified and seeds were acquired from IRRI and multiplied through the International Network for Genetic Evaluation of Rice (INGER)-Africa. Additional materials from AfricaRice and nominations from Madagascar, Ethiopia, Mali, Rwanda, and IRRI have also been multiplied. Off-season seed multiplication of cold-tolerant germplasm for highlands (japonica types) is under way at Hembeti, Morogoro, in Tanzania. The IRRI protocol for cold-tolerance screening in the screenhouse (cold-water tank method) and in the field was adopted and is being established for irrigated lowland conditions in Senegal and for high-altitude areas in Tanzania. In Tanzania, a screenhouse is being renovated for this purpose at the Sokoine University of Agriculture (SUA), Morogoro, in collaboration with the Horticulture Unit, Department of Crop Science and Production of SUA. In the field, planting-date trials with cold stress coinciding with either the early vegetative stage or reproductive stage are being conducted at Ndiaye, Senegal.
Suitable cold-affected screening sites identified for irrigated systems in Senegal and Mali, and for high-altitude sites in Rwanda, Ethiopia, and Madagascar
Suitable trial sites for on-station and on-farm trials for cold stress have been identified in Ethiopia (Adet, Holetta, and Jimma), Rwanda (Ntendezi, Cyili, Rwamagana, and Rutendeli), and Madagascar (Antsirabe and Mahitsy) for high-altitude screening and in Senegal (Ndiaye and Fanaye) and Mali (Kogoni) for irrigated systems.