1
|
Omondi DO, Dida MM, Berger DK, Beyene Y, Nsibo DL, Juma C, Mahabaleswara SL, Gowda M. Combination of linkage and association mapping with genomic prediction to infer QTL regions associated with gray leaf spot and northern corn leaf blight resistance in tropical maize. Front Genet 2023; 14:1282673. [PMID: 38028598 PMCID: PMC10661943 DOI: 10.3389/fgene.2023.1282673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Accepted: 10/18/2023] [Indexed: 12/01/2023] Open
Abstract
Among the diseases threatening maize production in Africa are gray leaf spot (GLS) caused by Cercospora zeina and northern corn leaf blight (NCLB) caused by Exserohilum turcicum. The two pathogens, which have high genetic diversity, reduce the photosynthesizing ability of susceptible genotypes and, hence, reduce the grain yield. To identify population-based quantitative trait loci (QTLs) for GLS and NCLB resistance, a biparental population of 230 lines derived from the tropical maize parents CML511 and CML546 and an association mapping panel of 239 tropical and sub-tropical inbred lines were phenotyped across multi-environments in western Kenya. Based on 1,264 high-quality polymorphic single-nucleotide polymorphisms (SNPs) in the biparental population, we identified 10 and 18 QTLs, which explained 64.2% and 64.9% of the total phenotypic variance for GLS and NCLB resistance, respectively. A major QTL for GLS, qGLS1_186 accounted for 15.2% of the phenotypic variance, while qNCLB3_50 explained the most phenotypic variance at 8.8% for NCLB resistance. Association mapping with 230,743 markers revealed 11 and 16 SNPs significantly associated with GLS and NCLB resistance, respectively. Several of the SNPs detected in the association panel were co-localized with QTLs identified in the biparental population, suggesting some consistent genomic regions across genetic backgrounds. These would be more relevant to use in field breeding to improve resistance to both diseases. Genomic prediction models trained on the biparental population data yielded average prediction accuracies of 0.66-0.75 for the disease traits when validated in the same population. Applying these prediction models to the association panel produced accuracies of 0.49 and 0.75 for GLS and NCLB, respectively. This research conducted in maize fields relevant to farmers in western Kenya has combined linkage and association mapping to identify new QTLs and confirm previous QTLs for GLS and NCLB resistance. Overall, our findings imply that genetic gain can be improved in maize breeding for resistance to multiple diseases including GLS and NCLB by using genomic selection.
Collapse
Affiliation(s)
- Dennis O. Omondi
- Department of Crops and Soil Sciences, School of Agriculture, Food Security and Environmental Sciences, Maseno University, Kisumu, Kenya
- Crop Science Division Bayer East Africa Limited, Nairobi, Kenya
| | - Mathews M. Dida
- Department of Crops and Soil Sciences, School of Agriculture, Food Security and Environmental Sciences, Maseno University, Kisumu, Kenya
| | - Dave K. Berger
- Department of Plant and Soil Sciences, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa
| | - Yoseph Beyene
- The Global Maize Program, International Maize and Wheat Improvement Center (CIMMYT), Nairobi, Kenya
| | - David L. Nsibo
- Department of Plant and Soil Sciences, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa
| | - Collins Juma
- Crop Science Division Bayer East Africa Limited, Nairobi, Kenya
- The Global Maize Program, International Maize and Wheat Improvement Center (CIMMYT), Nairobi, Kenya
| | - Suresh L. Mahabaleswara
- The Global Maize Program, International Maize and Wheat Improvement Center (CIMMYT), Nairobi, Kenya
| | - Manje Gowda
- The Global Maize Program, International Maize and Wheat Improvement Center (CIMMYT), Nairobi, Kenya
| |
Collapse
|
2
|
Welgemoed T, Duong TA, Barnes I, Stukenbrock EH, Berger DK. Population genomic analyses suggest recent dispersal events of the pathogen Cercospora zeina into East and Southern African maize cropping systems. G3 (BETHESDA, MD.) 2023; 13:jkad214. [PMID: 37738420 PMCID: PMC10627275 DOI: 10.1093/g3journal/jkad214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 08/03/2023] [Accepted: 09/06/2023] [Indexed: 09/24/2023]
Abstract
A serious factor hampering global maize production is gray leaf spot disease. Cercospora zeina is one of the causative pathogens, but population genomics analysis of C. zeina is lacking. We conducted whole-genome Illumina sequencing of a representative set of 30 C. zeina isolates from Kenya and Uganda (East Africa) and Zambia, Zimbabwe, and South Africa (Southern Africa). Selection of the diverse set was based on microsatellite data from a larger collection of the pathogen. Pangenome analysis of the C. zeina isolates was done by (1) de novo assembly of the reads with SPAdes, (2) annotation with BRAKER, and (3) protein clustering with OrthoFinder. A published long-read assembly of C. zeina (CMW25467) from Zambia was included and annotated using the same pipeline. This analysis revealed 790 non-shared accessory and 10,677 shared core orthogroups (genes) between the 31 isolates. Accessory gene content was largely shared between isolates from all countries, with a few genes unique to populations from Southern Africa (32) or East Africa (6). There was a significantly higher proportion of effector genes in the accessory secretome (44%) compared to the core secretome (24%). PCA, ADMIXTURE, and phylogenetic analysis using a neighbor-net network indicated a population structure with a geographical subdivision between the East African isolates and the Southern African isolates, although gene flow was also evident. The small pangenome and partial population differentiation indicated recent dispersal of C. zeina into Africa, possibly from 2 regional founder populations, followed by recurrent gene flow owing to widespread maize production across sub-Saharan Africa.
Collapse
Affiliation(s)
- Tanya Welgemoed
- Department of Biochemistry, Genetics and Microbiology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
| | - Tuan A Duong
- Department of Biochemistry, Genetics and Microbiology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
| | - Irene Barnes
- Department of Biochemistry, Genetics and Microbiology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
| | - Eva H Stukenbrock
- Environmental Genomics, Christian-Albrechts University of Kiel, Am Botanischen Garten 1-11, Kiel 24118, Germany
- Max Planck Institute for Evolutionary Biology, August-Thienemann-Str. 2, Plön 24306, Germany
| | - Dave K Berger
- Department of Plant and Soil Sciences, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
| |
Collapse
|
3
|
Deep Learning Diagnostics of Gray Leaf Spot in Maize under Mixed Disease Field Conditions. PLANTS 2022; 11:plants11151942. [PMID: 35893646 PMCID: PMC9330607 DOI: 10.3390/plants11151942] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/14/2022] [Revised: 07/13/2022] [Accepted: 07/22/2022] [Indexed: 11/30/2022]
Abstract
Maize yields worldwide are limited by foliar diseases that could be fungal, oomycete, bacterial, or viral in origin. Correct disease identification is critical for farmers to apply the correct control measures, such as fungicide sprays. Deep learning has the potential for automated disease classification from images of leaf symptoms. We aimed to develop a classifier to identify gray leaf spot (GLS) disease of maize in field images where mixed diseases were present (18,656 images after augmentation). In this study, we compare deep learning models trained on mixed disease field images with and without background subtraction. Performance was compared with models trained on PlantVillage images with single diseases and uniform backgrounds. First, we developed a modified VGG16 network referred to as “GLS_net” to perform binary classification of GLS, which achieved a 73.4% accuracy. Second, we used MaskRCNN to dynamically segment leaves from backgrounds in combination with GLS_net to identify GLS, resulting in a 72.6% accuracy. Models trained on PlantVillage images were 94.1% accurate at GLS classification with the PlantVillage testing set but performed poorly with the field image dataset (55.1% accuracy). In contrast, the GLS_net model was 78% accurate on the PlantVillage testing set. We conclude that deep learning models trained with realistic mixed disease field data obtain superior degrees of generalizability and external validity when compared to models trained using idealized datasets.
Collapse
|