Abstract
Striga hermonthica is the most important parasitic weed in sub-Saharan Africa and remains one of the most devastating biotic factors affecting sorghum production in the western regions of Kenya. Farmers have traditionally managed Striga using cultural methods, but the most effective and practical solution to poor smallholder farmers is to develop Striga-resistant varieties. This study was undertaken with the aim of identifying new sources of resistance to Striga in comparison with the conventional sources as standard checks. We evaluated 64 sorghum genotypes consisting of wild relatives, landraces, improved varieties, and fourth filial generation (F4) progenies in both a field trial and a pot trial. Data were collected for days to 50% flowering (DTF), dry panicle weight (DPW, g), plant height (PH, cm), yield (YLD, t ha−1), 100-grain weight (HGW, g), overall disease score (ODS), overall pest score (OPS), area under Striga number progress curve (ASNPC), maximum above-ground Striga (NSmax), and number of Striga-forming capsules (NSFC) at relevant stages. Genetic diversity and hybridity confirmation was determined using Diversity Arrays Technology sequencing (DArT-seq). Residual heterosis for HGW and NSmax was calculated as the percent increase or decrease in performance of F4 crossover midparent (MP). The top 10 best yielding genotypes were predominantly F4 crosses in both experiments, all of which yielded better than resistant checks, except FRAMIDA in the field trial and HAKIKA in the pot trial. Five F4 progenies (ICSVIII IN × E36-1, LANDIWHITE × B35, B35 × E36-1, F6YQ212 × B35, and ICSVIII IN × LODOKA) recorded some of the highest HGW in both trials revealing their stability in good performance. Three genotypes (F6YQ212, GBK045827, and F6YQ212xB35) and one check (SRN39) were among the most resistant to Striga in both trials. SNPs generated from DArT-seq grouped the genotypes into three major clusters, with all resistant checks grouping in the same cluster except N13. We identified more resistant and high-yielding genotypes than the conventional checks, especially among the F4 crosses, which should be promoted for adoption by farmers. Future studies will need to look for more diverse sources of Striga resistance and pyramid different mechanisms of resistance into farmer-preferred varieties to enhance the durability of Striga resistance in the fields of farmers.
Highlights
Sorghum [Sorghum bicolor (L.) Moench] is a diploid (2n = 2x = 20) cereal grass of the Gramineae family native to Africa (Doggett, 1988)
There were significant differences (P ≤ 0.001) in the performance of the parental lines when compared with the progenies, except for days to 50% flowering (DTF) in the field trial and PH
More consistency across replications was observed in the field trial for area under Striga number progress curve (ASNPC) and overall disease score (ODS) and in the pot trial for number of Strigaforming capsules (NSFC) and ODS (Table 3)
Summary
Sorghum [Sorghum bicolor (L.) Moench] is a diploid (2n = 2x = 20) cereal grass of the Gramineae family native to Africa (Doggett, 1988). It is the fifth most important cereal globally (Kiprotich et al, 2015) and a major staple food for more than 300 million inhabitants of Africa (Kidanemaryam et al, 2018). Drought stress and poor soil fertility are the major abiotic factors affecting sorghum production in semi-arid areas (Ejeta and Knoll, 2007). It remains one of the most devastating biotic factors affecting sorghum production in the western regions of Kenya (Khan et al, 2006) often characterized by low fertility and high moisture stress. The growth and development of the host plants become severely affected resulting in yield losses of up to 100% (Kim et al, 2002; Ejeta, 2007)
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