GENETIC STUDIES AND RELATED AGRONOMIC STRATEGIES FOR STRIGA CONTROL IN SORGHUM [SORGHUM BICOLOR (L) MOENCH] PRODUCTION IN NIGER
Striga hermonthica is a harmful obligate hemi parasite of cereal crops which causes impediment to sorghum cultivation in Niger. Thus, over the years, several control methods including ethylene gas utilization, nitrogen and fertilizer application, crop rotation, etc. were tested around the world, but some of them are not accessible to small holder farmers with limited resources. The development of striga resistant sorghum varieties with farmers' preferred traits is the best strategy to minimize striga damage on smallholder farms and contribute to food security. The objectives of this study were to: (i) determine sorghum production constraints and farmers' preferences for improved sorghum varieties in Niger, (ii) assess available sorghum genotypes for high yield and Striga resistance in Niger, (iii) establish the effectiveness of DAP Diammonium phosphate and Sesame (Sesamum indicum) in controlling Striga, (iv) determine the breeding potential of sorghum populations for Striga hermonthica resistance and grain yield.
A participatory rural appraisal (PRA) study was carried out to identify farmers' preferred varieties and traits, and sorghum production constraints using 200 sorghum growers at Maradi and Tahoua regions. Respectively, 55% and 43% of the growers in Maradi and Tahoua were affected by rainfall scarcity and striga attack. Among the growers, 31% of the farmers in Tahoua and 19% in Maradi indicated that they were affected by the weed. Varieties 'Mota Maradi' and 'Eltsedaoua' were the varieties with highest farmers' preferences in Maradi and Tahoua respectively. In addition, white seeded sorghum grain was by far farmers' most preferred sorghum colour (more than 50% of the farmers in two regions). Farmers' other preferred traits were medium height, high tillering capacity number, high grain weight and resistance to Striga. Three levels each of DAP (0 g, 2 g and 5 g) and Sesame seeds (0 g, 0.5 g and 1.5 g) were evaluated for their effects on striga and sorghum grain yield improvement in 2017 and 2018 at Konni station. The DAP level one micro dosing (2 g) applied alone and the sesame level two
(1.5 g) application alone significantly reduced striga emergence and distribution. The interaction of sesame and DAP also increased grain yield. Two field studies to identify sorghum genotypes with high yield and Striga resistance in Niger were undertaken in 2017 and 2018 rainy season at Konni station. The genotypes P9401, P9403, Brahan, S35, CE-151-262, P406 and TXN13/BC3F5-41 were found to have high yield with medium height, high number of panicles, high grain weight and highly resistant to Striga. Two breeding population were developed by crossing P9401and Eltsedaoua and also Mota Maradi with F2-20. The backcross populations were then evaluated in two different locations in Tahoua region, for yield and tolerance to Striga. The populations BC1F2 (P9401 X Eltsedaoua) and BC1F2 (F2-20 x Mota Maradi) were selected as sources of Striga resistant lines based on the selection criteria used. Findings of this thesis have paved the road for a strong future breeding program in Niger to reduce sorghum yield loss due to Striga hermonthica.