Integrated Striga management in Sorghum through resistance breeding and biocontrol in the semi-arid regions of Tanzania.

Doctor of Philosophy in Plant Breeding. University of KwaZulu-Natal, Pietermaritzburg, 2017.Abstract available in PDF file

Combining ability of yield and yield components among Fusarium oxysporum f.sp. strigae-compatible and Striga-resistant sorghum genotypes

Use of sorghum [Sorghum bicolor (L.) Moench] cultivars with partial resistance to Striga spp. and Fusarium oxysporum f.sp. strigae (FOS) represents a novel strategy to control Striga. This study aimed to identify the nature of gene action controlling grain yield and yield components and to select promising sorghum crosses possessing both FOS compatibility and Striga resistance, along with good combining ability effects. One-hundred hybrids, developed from pairwise matings among 10 FOS compatible, high-yielding female lines and 10 Striga-resistant male lines, were evaluated with and without FOS inoculation. The F1s were field evaluated at three locations in Tanzania known for their severe Striga infestation, using an alpha lattice design with two replications. General (GCA) and specific combining ability (SCA) variances were significant for grain yield per plant, hundred-seed weight, plant height, flowering time and the number of Striga plants. The study demonstrated FOS inoculation to be an effective means of controlling Striga. Families 675 × 672, AS435 × 3993 and 4643 × AS436 displaying large SCA effects for grain yield, and 4567 × AS429, 3424 × AS430 and 3424 × AS436 with small SCA effects for Striga counts should be useful genetic resources for breeding and integrated Striga management

Screening of sorghum genotypes for resistance to Striga hermonthica and S. asiatica and compatibility with Fusarium oxysporum f.sp. strigae

In the semi-arid areas of Tanzania, yield losses of sorghum [Sorghum biocolor (L.) Moench] due to Striga hermonthica (Sh) and S. asiatica (Sa) infestations are estimated to be 30–90%. The use of resistant sorghum varieties compatible with Fusarium oxysporum f.sp. strigae (FOS), a biocontrol agent of Striga, may supress the weed and enhance the crop productivity. The objective of this study was to screen and select farmer-preferred sorghum genotypes for Sh and Sa resistance and FOS compatibility for resistance breeding under Tanzanian conditions. Sixty sorghum genotypes were evaluated under screen house conditions using Sh- and Sa-infested field soils with controlled seed infestation, with or without inoculation of the sorghum seeds with FOS. Inoculation of sorghum seeds with FOS significantly enhanced sorghum growth and productivity, and supressed Sh and Sa growth and development. There were reductions of 1–4 Sh and Sa plants when sorghum seeds were inoculated with FOS. Overall, we selected 25 promising sorghum lines resistant to Sh and/or Sa, and with FOS compatibility. The selected sorghum lines are valuable genetic resources for the development of Striga management in sorghum through the integrated use of host resistance and FOS inoculation

Management of the Striga epidemics in pearl millet production: a review

Abstract Pearl millet (Pennisetum glaucum [L.] R. Br.) is a drought-resilient and nutritious staple food crop widely cultivated in arid and semi-arid regions. Worldwide, pearl millet is ranked the 6th most widely produced cereal crop after wheat, rice, maize, barley, and sorghum, with a total production of 30.5 million tons on 32.1 million hectares. In Burkina Faso, it is the 3rd widely cultivated crop next to sorghum and maize, with a mean yield of 0.8 ton ha−1, far below the potential yield of 3.0 tons ha−1 attributable to various production challenges. Among the production constraints, the parasitic weed Striga species, particularly S. hermonthica is endemic and causes up to 80% yield losses under heavy infestation. Different control methods (e.g., cultural practices, chemicals and bio-herbicides) have been recommended, but they have been largely ineffective due to diverse and complex problems, including the life cycle, seed production, and prolonged seed dormancy of S. hermonthica; poor access and cost of implementation. Breeding for host plant resistance presents a cost-effective, environmentally friendly and affordable method for smallholder farmers to control and reduce Striga infestations and improve pearl millet yields. Therefore, the objectives of this study were to present the impact of S. hermonthica damage on pearl millet production and productivity and assess the effectiveness of different management methods of S. hermonthica with an emphasis on host plant resistance. The first section of the review assesses the impact of Striga infestation on pearl millet production, followed by the developmental stages of Striga, Striga infestation and damage management strategies, breeding for Striga resistance and other Striga control methods. The paper summarises genetic resources, new breeding technologies, and innovations for the precision and speed breeding of Striga-resistant cultivars. The review will guide the use of the best breeding strategies and accelerate the breeding of new pearl millet cultivars that are best-performing and resistant to S. hermonthica to reduce damage incurred by Striga infestations on farmers’ fields in Burkina Faso and related agro-ecologies

Genome-wide association analyses of agronomic traits and Striga hermonthica resistance in pearl millet

Abstract Pearl millet (Pennisetum glaucum [L.] R. Br.) is a nutrient-dense, relatively drought-tolerant cereal crop cultivated in dry regions worldwide. The crop is under-researched, and its grain yield is low (< 0.8 tons ha−1) and stagnant in the major production regions, including Burkina Faso. The low productivity of pearl millet is mainly attributable to a lack of improved varieties, Striga hermonthica [Sh] infestation, downy mildew infection, and recurrent heat and drought stress. Developing high-yielding and Striga-resistant pearl millet varieties that satisfy the farmers’ and market needs requires the identification of yield-promoting genes linked to economic traits to facilitate marker-assisted selection and gene pyramiding. The objective of this study was to undertake genome-wide association analyses of agronomic traits and Sh resistance among 150 pearl millet genotypes to identify genetic markers for marker-assisted breeding and trait introgression. The pearl millet genotypes were phenotyped in Sh hotspot fields and screen house conditions. Twenty-nine million single nucleotide polymorphisms (SNPs) initially generated from 345 pearl millet genotypes were filtered, and 256 K SNPs were selected and used in the present study. Phenotypic data were collected on days to flowering, plant height, number of tillers, panicle length, panicle weight, thousand-grain weight, grain weight, number of emerged Striga and area under the Striga number progress curve (ASNPC). Agronomic and Sh parameters were subjected to combined analysis of variance, while genome-wide association analysis was performed on phenotypic and SNPs data. Significant differences (P < 0.001) were detected among the assessed pearl millet genotypes for Sh parameters and agronomic traits. Further, there were significant genotype by Sh interaction for the number of Sh and ASNPC. Twenty-eight SNPs were significantly associated with a low number of emerged Sh located on chromosomes 1, 2, 3, 4, 6, and 7. Four SNPs were associated with days-to-50%-flowering on chromosomes 3, 5, 6, and 7, while five were associated with panicle length on chromosomes 2, 3, and 4. Seven SNPs were linked to thousand-grain weight on chromosomes 2, 3, and 6. The putative SNP markers associated with a low number of emerged Sh and agronomic traits in the assessed genotypes are valuable genomic resources for accelerated breeding and variety deployment of pearl millet with Sh resistance and farmer- and market-preferred agronomic traits