Plant Gene and Trait 2024, Vol.15, No.6, 295-304 http://genbreedpublisher.com/index.php/pgt 298 Genotypic characterization, on the other hand, involves the use of molecular markers such as single nucleotide polymorphisms (SNPs) and simple sequence repeats (SSRs) to assess genetic diversity and population structure. For example, the USDA-NPGS Ethiopian sorghum germplasm collection was genotyped using SNP markers, revealing high genetic diversity and the presence of unique alleles (Cuevas et al., 2016). Another study utilized SSR markers to develop a sorghum diversity research set, which helped in understanding the genetic relationships among accessions from different geographic regions (Shehzad et al., 2009). These genotypic analyses are essential for identifying distinct cluster groups and sub-populations, which can be used to improve the utilization of germplasm in breeding programs. 4.2 Establishment of classification standards and their application in germplasm banks The establishment of classification standards is vital for the effective management and utilization of sorghum germplasm resources in genebanks. These standards typically involve the development of core and mini core collections that represent the genetic diversity of the entire germplasm collection. For instance, the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) developed a mini core collection of sorghum, which comprises 1% of the entire collection. This mini core collection has been extensively used for identifying sources of resistance to various stresses and for agronomic and grain nutritional traits (Upadhyaya et al., 2009). Classification standards also include the use of high-throughput phenotyping platforms and genome-wide association studies (GWAS) to link phenotypic traits with genotypic data. This approach has been employed to identify genomic regions associated with important agronomic traits and resistance to biotic and abiotic stresses (Upadhyaya et al., 2016). Additionally, the use of hierarchical cluster analysis and principal component analysis (PCA) helps in grouping germplasm accessions based on their genetic and phenotypic similarities, which aids in the selection of parents for breeding programs (Mulima et al., 2018). 4.3 A Systematic classification method for sorghum germplasm resources in Ethiopia Ethiopia is a center of diversity for sorghum, and a systematic classification method has been developed to manage its rich germplasm resources. A comprehensive study involving 2010 Ethiopian sorghum accessions was conducted, where phenotypic data were collected for various traits across multiple locations. A subset of 1628 accessions was genotyped using sequencing techniques, which revealed high genetic diversity and the presence of rare natural variations (Girma et al., 2020). The genotypic analysis identified distinct cluster groups and sub-populations, which were used to create a core subset of 387 lines. This core subset was selected based on cluster groups obtained through genotyping-by-sequencing (GBS) analysis, followed by stratified random sampling using quantitative traits. The classification method also involved genome-environment association analysis, which identified candidate genes associated with adaptation to abiotic factors. This information is crucial for exploiting the adaptive potential of sorghum to different environments (Girma et al., 2020). The systematic classification of Ethiopian sorghum germplasm has provided valuable insights into the diversity and relationship of sorghum collections, facilitating their effective utilization in breeding programs and conservation efforts. 5 Discovery and Breeding Application of Sorghum Drought Resistance Genes 5.1 Selection criteria for case studies The selection of case studies for the discovery and breeding application of sorghum drought resistance genes was based on several criteria. Firstly, studies that utilized diverse sorghum genotypes under varying environmental conditions were prioritized to ensure a comprehensive understanding of drought resistance mechanisms. Secondly, research that employed advanced genomic and transcriptomic techniques to identify and map drought resistance genes was included. Lastly, studies that demonstrated practical applications of these genes in breeding programs were considered essential to highlight the translational aspect of the research. 5.2 Discovery process of drought resistance genes The discovery of drought resistance genes in sorghum has been facilitated by various genomic and transcriptomic approaches. For instance, transcriptome analysis of drought-resistant and drought-sensitive sorghum genotypes
RkJQdWJsaXNoZXIy MjQ4ODYzMg==