Browsing by Person "Gaikpa, David Sewordor"

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Breeding for resistance to Fusarium ear diseases in maize and small-grain cereals using genomic tools
(2021) Gaikpa, David Sewordor; Miedaner, Thomas
The world’s human and livestock population is increasing and there is the need to increase quality food production to achieve the global sustainable development goal 3, zero hunger by year 2030 (United Nations, 2015). However, biotic stresses such as Fusarium ear infections pose serious threat to cereal crop production. Breeding for host plant resistance against toxigenic Fusarium spp. is a sustainable way to produce more and safer cereal crops such as maize and small-grain winter cereals. Many efforts have been made to improve maize and small-grain cereals for ear rot (ER) and Fusarium head blight (FHB) resistances, using conventional and genomic techniques. Among small-grain cereals, rye had the shortest maturity period followed by the descendant, hexaploid triticale while both wheat species had the longest maturity period. In addition, rye and triticale were more robust to Fusarium infection and deoxynivalenol accumulation, making them safer grain sources for human and animal consumption. However, a few resistant cultivars have been produced by prolonged conventional breeding efforts in durum wheat and bread wheat. High genetic variation was present within each crop species and can be exploited for resistance breeding. In this thesis, the genetic architecture of FHB resistance in rye was investigated for the first time, by means of genome-wide association study (GWAS) and genomic prediction (GP). GWAS detected 15 QTLs for Fusarium culmorum head blight severity, of which two had major effects. Both weighted and unweighted GP approaches yielded higher prediction abilities than marker-assisted selection (MAS) for FHB severity, heading stage and plant height. Genomics-assisted breeding can shorten the duration of breeding rye for FHB resistance. In the past decade, genetic mapping and omics were used to identify a multitude of QTLs and candidate genes for ear rot resistances and mycotoxin accumulation in maize. The polygenic nature of resistance traits, high genotype x environment interaction, and large-scale phenotyping remain major bottlenecks to increasing genetic gains for ear rots resistance in maize. Phenotypic and molecular analyses of DH lines originating from two European flint landraces (“Kemater Landmais Gelb”, KE, and “Petkuser Ferdinand Rot”, PE) revealed high variation for Gibberella ear rot (GER) severity and three agronomic traits viz. number of days to female flowering, plant height and proportion of kernels per cob. By employing multi-SNP GWAS method, we found four medium-effect QTLs and many small-effect (10) QTLs for GER severity in combined DH libraries (when PCs used as fixed effects), none co-localized with the QTLs detected for the three agronomic traits analyzed. However, one major QTL was detected within KE DH library for GER severity. Two prioritized SNPs detected for GER resistance were associated with 25 protein-coding genes placed in various functional categories, which further enhances scientific knowledge on the molecular mechanisms of GER resistance. Genome-based approaches seems promising for tapping GER resistance alleles from European maize landraces for applied breeding. After several cycles of backcrossing and sufficient selection for agronomic adaptation traits, the resistant lines identified in this thesis can be incorporated into existing maize breeding programs to improve immunity against F. graminearum ear infection. Breeding progress can be faster using KE landrace than PE. A successful validation of QTLs identified in this thesis can pave way for MAS in rye and marker-assisted backcrossing in maize. Effective implementation of genomic selection requires proper design of the training and validation sets, which should include part of the current breeding population.
Exploiting genetic diversity in two European maize landraces for improving Gibberella ear rot resistance using genomic tools
(2021) Gaikpa, David Sewordor; Kessel, Bettina; Presterl, Thomas; Ouzunova, Milena; Galiano-Carneiro, Ana L.; Mayer, Manfred; Melchinger, Albrecht E.; Schön, Chris-Carolin; Miedaner, Thomas
Fusarium graminearum (Fg) causes Gibberella ear rot (GER) in maize leading to yield reduction and contamination of grains with several mycotoxins. This study aimed to elucidate the molecular basis of GER resistance among 500 doubled haploid lines derived from two European maize landraces, “Kemater Landmais Gelb” (KE) and “Petkuser Ferdinand Rot” (PE). The two landraces were analyzed individually using genome-wide association studies and genomic selection (GS). The lines were genotyped with a 600-k maize array and phenotyped for GER severity, days to silking, plant height, and seed-set in four environments using artificial infection with a highly aggressive Fg isolate. High genotypic variances and broad-sense heritabilities were found for all traits. Genotype-environment interaction was important throughout. The phenotypic (r) and genotypic (rg) correlations between GER severity and three agronomic traits were low (r= − 0.27 to 0.20; rg = − 0.32 to 0.22). For GER severity, eight QTLs were detected in KE jointly explaining 34% of the genetic variance. In PE, no significant QTLs for GER severity were detected. No common QTLs were found between GER severity and the three agronomic traits. The mean prediction accuracies (p) of weighted GS (wRR-BLUP) were higher than p of marker-assisted selection (MAS) and unweighted GS (RR-BLUP) for GER severity. Using KE as the training set and PE as the validation set resulted in very low p that could be improved by using fixed marker effects in the GS model.
Multi-parent QTL mapping reveals stable QTL conferring resistance to Gibberella ear rot in maize
(2021) Galiano-Carneiro, Ana L.; Kessel, Bettina; Presterl, Thomas; Gaikpa, David Sewordor; Kistner, Maria Belen; Miedaner, Thomas
Maize production is on risk by Gibberella ear rot (GER) caused by Fusarium graminearum. This is one of the most important ear rot diseases in temperate zones as it leads to yield losses and production of harmful mycotoxins. We investigated, for the first time, the potential use of Brazilian tropical maize to increase resistance levels to GER in temperate European flint germplasm by analyzing six interconnected biparental populations. We assessed GER symptoms in Brazil and in Europe in up to six environments (= location × year combinations) during the growing seasons of 2018 and 2019. We conducted multi-parent QTL and biparental QTL mapping, and identified four QTLs with additive gene action, each explaining 5.4 to 21.8% of the total genotypic variance for GER resistance. Among them, QTL q1 was stable across test environments, populations, and between inbred lines and testcrosses. The accuracies of genomic prediction ranged from 0.50 to 0.59 depending on the resistance donor and prediction model. Jointly, our study reveals the potential use of Brazilian resistance sources to increase GER resistance levels by genomics-assisted breeding.