GENETIC IMPROVEMENT OF LOCAL SORGHUM (Sorghum bicolor L. Moench) VARIETIES FOR DROUGHT TOLERANCE

ABSTRACT

Drought is the major abiotic factor limiting crop production worldwide. Sorghum is one of the most drought tolerant grain crops that have the ability of addressing food insecurity in semi-arid areas. However, it is exposed recurrently to severe forms of drought and therefore, requires improvement to cope with moisture stress. The present investigation was undertaken to improve local sorghum varieties for drought tolerance in Burkina Faso. A participatory Rural Appraisal was conducted to identify farmers’ constraints and to determine their preferred sorghum varieties. One hundred and ten accessions, including improved and introduced materials, were assessed in full irrigated and terminal drought conditions in an alpha lattice design to identify drought tolerant and high yielding genotypes. A molecular characterization using 26 SSRs markers was conducted with the same accessions to determine the genetic diversity, genetic differentiation and the level of homozygosity of these accessions. Finally, marker-assisted backcrossing was carried out to introgress stay-green QTLs into four farmers’ preferred varieties. The major constraint limiting sorghum production in Burkina Faso was Striga, a parasitic weed. Drought was the second most important factor reducing sorghum yield and the most important abiotic constraint. The study revealed that terminal moisture stress was the most frequent type of drought but has less effect on yield than pre-flowering drought. Forty seven per cent of farmers rely preferentially on their local landraces. A few preferred improved varieties derived from local landraces, over high yielding exotic (introduced) varieties. Among released varieties, farmers grew more Kapelga in all different climatic zones of the country. There was a strong correlation between grain filling rates, yield under stress, grain number, Stress Tolerance Index (STI) and Geometric Mean Productivity (GMP). This indicates that improvement can be achieved using accessions with high STI and GMP indices. Classification based on yield and its components, divided accessions into three main groups. Grinkan was the highest yielding and most drought tolerant genotype in the study. A group of high yielding and drought susceptible accessions were identified including local improved varieties and landraces that performed well under non-stressed conditions and were susceptible to terminal drought. Low yielding and drought tolerant accessions were also identified. Genotypes with high STI indices could be used by farmers to ensure optimal production in drought prone areas and in breeding programs. There was low gene diversity of 0.34 compared to previous molecular studies in Burkina Faso. The Fixation index (Fst) value exhibited low genetic differentiation among populations and moderate genetic differentiation between local population and exotic materials. The local accessions have a high level of homozygosity.

Five stay-green QTLs (Stg1, Stg2, Stg3, Stg4 and StgB) were incorporated into four recurrent (Kapelga, Sariaso09, Sariaso01 and Grinkan) backgrounds. The BC1F1 lines which carried at least one QTL included eighteen (18) progenies from Sariaso09 and two from Kapelga which were heterozygous at all marker loci flanking the target QTLs. Four, three and four progenies, respectively, from Grinkan, Kapelga and Sariaso01 carried four QTLs. Only one plant, GB7, carried three major QTLs (Stg1, Stg2 and Stg4). Seven, four, three and one progenies, respectively, from Sariaso09, Kapelga, Grinkan and Sariaso01 carried two stay-green QTLs. Fifteen, one and one progenies, respectively from Sariaso09, Kapelga and Sariaso01 carried one QTL for stay-green. The screening using background markers identified progenies with different recovery rates of the recurrent parent genome. A majority of the progenies recovered less than 75% of the recurrent parent genome. Two progenies (GB8 and S1B3) recovered 75% of their recurrent parent genome. Three (S9B73, KB4 and GB7), two (S9B48 and KB16) and one (S1B6) progenies had respectively recovered 78%, 81% and 83% of the recurrent parent. The best 30 accessions identified through phenotypic evaluation and the promising advanced introgression lines should be evaluated in different locations for possible release as commercial varieties. In the future, drought tolerant lines developed through MABC and high yielding lines could help stakeholders to improve their sorghum production, and, therefore, contribute to ensure food security in Burkina Faso.