Guinea sorghum hybrids: bringing the benefits of hybrid technology to a staple crop of Sub-Saharan Africa

 A. Toure, F. Rattunde, D. Sansan & E. Weltzien

Guinea sorghums predominate throughout the Savannah sorghum belt, accounting for more than 70% of all sorghum grown, and for more than 90% in the 600+ mm rainfall zone. The guinea sorghums are characterized by high food grain quality, weathering and insect resistance, good grain storage, and good adaptation to poor soils. Considerable efforts have been made to breed higher-yielding sorghums using exotic non-Guinea germplasm. The varieties and hybrids based on exotic germplasm, however, did not prove to be a viable option in this zone except for special niche conditions. The use of hybrid vigor offers the potential to achieve significant productivity gains but has not yet been explored due to the lack of hybrid parental lines of Guinea background. This project is developing maintainer/male-sterile (AB) pairs of Guinea background and beginning to characterize the levels of heterosis and combining ability within this race. The genetic materials used include landrace varieties identified by researchers on the basis of higher productivity, stability of yield over multi-environment tests, panicle progenies selected by farmers within their own varieties, breeding lines from the IER pedigree program, and the Guinea core collection. More than 300 testcross F1s of Guinea-race landraces and lines crossed with A1 cytoplasmic tester lines were made and evaluated for their fertility reaction in Mali. The results showed that more than half of all varieties tested showed maintainer reactions. A total of 24 lines were identified that showed good maintainer reaction. Large intra-varietal (plant-to-plant) variation for fertility reaction exists, especially within the landrace varieties. Uniform restorer reaction was shown by 7 varieties.  Good frequencies of both maintainer and restorer reactions occur among Guinea-race sorghums from West Africa and should facilitate the development of hybrid parents. Significant progress was made to develop male-sterile lines from the maintainer lines identified. The fourth backcross generation was completed for CSM 335(2 lines), CSM 207 (15), CSM 219 (11), and Fambé (2). The third backcross generation was completed for IPS 0001 (5), 98-BE-F5P-82 (5), 97SB-F5DT-150 (5), and 97-SU-F5DT-151 (1). The establishment of two off-season generations using dark cages to obtain flowering accelerated the breeding process, enabling the production of A/B male-sterile pairs in the backcross 5 generation in less than three years. Trials are being initiated to determine the heterosis levels and characterize combining ability among diverse guinea-race accessions from a Guinea core collection. The parental lines represent western, eastern and southern Africa as well as Asia.  They also have contrasting grain size, panicle architecture, plant height, and maturity. Future research should broaden the genetic base of hybrid parents using agronomic trait characterization data and molecular genetic characterization of the structure of genetic diversity within the Guinea race. The identification of heterotic patterns and development of an ideotype(s) for guinea-race hybrid parents will facilitate efficient hybrid development.