Identification of QTLs for grain yield and other traits in tropical maize under Striga infestation

Abstract

Striga is an important biotic factor limiting maize production in sub-Saharan Africa and can cause yield losses as high as 100%. Marker-assisted selection (MAS) approaches hold a great potential for improving Striga resistance but requires identification and use of markers associated with Striga resistance for adequate genetic gains from selection. However, there is no report on the discovery of quantitative trait loci (QTL) for resistance to Striga in maize under artificial field infestation. In the present study, 198 BC 1 S 1 families obtained from a cross involving TZEEI 29 ( Striga resistant inbred line) and TZEEI 23 ( Striga susceptible inbred line) plus the two parental lines were screened under artificial Striga- infested conditions at two Striga -endemic locations in Nigeria in 2018, to identify QTL associated with Striga resistance indicator traits, including grain yield, ears per plant, Striga damage and number of emerged Striga plants. Genetic map was constructed using 1,386 DArTseq markers distributed across the 10 maize chromosomes, covering 2076 cM of the total genome with a mean spacing of 0.11 cM between the markers. Using composite interval mapping (CIM), fourteen QTL were identified for key Striga resistance/tolerance indicator traits: 3 QTL for grain yield, 4 for ears per plant and 7 for Striga damage at 10 weeks after planting (WAP), across environments. Putative candidate genes which encode major transcription factor families WRKY, bHLH, AP2-EREBPs, MYB, and bZIP involved in plant defense signaling were detected for Striga resistance/tolerance indicator traits. The QTL detected in the present study would be useful for rapid transfer of Striga resistance/tolerance genes into Striga susceptible but high yielding maize genotypes using MAS approaches after validation. Further studies on validation of the QTL in different genetic backgrounds and in different environments would help verify their reproducibility and effective use in breeding for Striga resistance/tolerance.

Genetic dissection of Striga hermonthica (Del.) Benth. resistance via genome-wide association and genomic prediction in tropical maize germplasm

“…High broad-sense heritability estimates for GY, AUSNPC, SDR and number of emerged Striga plants 12 WAP suggest that the actual narrow-sense heritability could be higher and that reasonable genetic gain for these traits could be expected. The high broad-sense heritability estimates for GY (0.70) and number of emerged Striga plants 12 WAP (0.68) observed in this study corroborate previous reports under artificial Striga infestation (Menkir et al 2012 ; Makumbi et al 2015 ; Adewale et al 2020 ) and higher than the heritability observed in biparental populations (Badu-Apraku et al 2020a , b ).…”

“…On the other hand, one SNP S3_158421414 detected consistently for number of emerged Striga plants at 10 and 12 WAP and AUSNPC was overlapped with the QTL reported by Badu-Apraku et al ( 2020a ) in biparental population. In this study, no overlapping of SNPs was detected between number of Striga -emerged plants and SDR, however five SNPs on chromosome 3 ( S3_143803575 , S3_143804650, S3_145603175, S3_145603187 and S3_158421414 ) detected for number of Striga -emerged plants were overlapped with four QTL detected for SDR in an earlier study (Badu-Apraku et al 2020b ) which suggests this region might be carrying an important gene/s for resistance to Striga .…”

“…Plots were thinned to one plant per hill two weeks after planting to attain a population density of approximately 53,333 plants per hectare. The recommended fertilizer rate was reduced, and application was delayed up to three weeks after planting to induce the production of strigolactones which stimulate good germination of the Striga seeds and the attachment of the Striga plants to the roots of host plants (Adewale et al 2020 ; Badu-Apraku et al 2020a , b ). Weeding was done by hand to remove all weeds from the field except S. hermonthica .…”

Genome-Wide Association Studies for Striga asiatica Resistance in Tropical Maize

“…The development of resistance has proven to be strenuous due to its low heritability [ 16 , 17 ]. Marker identification will formulate tools that are faster, cheaper, and easier to utilise in effectively tackling the problem of breeding for Striga resistance [ 13 , 18 , 19 ]. There is a research gap on the use of SNP markers to improve maize genotypes to resist Striga infestation [ 20 ].…”

“…There is need to identify SNP markers in maize that are associated with resistance to Striga using genome-wide association study (GWAS) because SNP markers are abundantly available in the maize genome, codominant, evenly distributed throughout the genome, and highly reproducible and polymorphic. However, to date, only reports exist for Striga hermonthica found in east Africa and absent for Striga asiatica found in southern Africa [ 13 , 18 , 21 , 22 ]. Identification of SNP markers will solidify convectional breeding methods and bring rejuvenation to maize production in resource poor African farmers by reducing yield losses due to Striga infestation [ 13 ].…”