Tree Genetics and Molecular Breeding 2024, Vol.14, No.1, 22-31 http://genbreedpublisher.com/index.php/tgmb 26 Table 1 Broad-sense heritability calculated on a plot-mean basis and SNP heritability estimates, variance components and coefficients of variation of 14 traits in cassava GWAS panel (Adopted from Rabbi et al., 2020) Trait SNP-h2 H2 σg σg×e σe CV CMD severity 0.434 0.766 0.783 0.086 0.140 63 CGM severity 0.165 0.149 0.074 0.177 0.244 19 Apical pubescence 0.502 0.531 0.175 0.083 0.071 113 Leaf shape 0.499 0.510 0.679 0.475 0.178 22 Apical leaf colour 0.496 0.567 1.160 0.629 0.601 23 Mature leaf greenness 0.586 0.531 0.427 0.186 0.191 18 Petiole colour 0.716 0.754 3.322 0.602 0.485 33 Harvest index 0.308 0.538 0.010 0.002 0.007 28 Plant type 0.384 0.369 0.376 0.180 0.465 38 Quter stem colour 0.516 0.388 0.907 0.191 1.241 22 Total carotenoids content (colour chart) 0.675 0.726 0.401 0.066 0.085 49 Dry matter content 0.565 0521 14.776 3.385 10.184 15 Root periderm colour 0.548 0.610 0.190 0.035 0.086 19 Root cortex colour 0.518 0.415 0.070 0.036 0.062 20 Note: H2 is the broad-sense heritablity, σg is the clonal genotypic variance, σg×e is the variance due to genotype by environment (G×E), andσe is the being the residual variance 4.3 Application of molecular markers and genomics in cassava improvement Molecular marker-assisted selection (MAS) plays a key role in cassava improvement, especially in accelerating the selection process for genetic traits. By utilizing specific molecular markers, such as single nucleotide polymorphisms (SNPS) and simple sequence repeats (SSRS), breeders are able to more precisely select plants with desired traits. A study by Mba et al. (2001) using SSR markers provided a preliminary molecular genetic map of the cassava genome, which helped to locate quantitative trait loci (QTL) and genetic analysis, thereby improving the efficiency and accuracy of breeding. In addition, genotyping based on high-throughput sequencing (NGS) techniques, such as Genotyping by sequencing (GBS), has emerged as a highly effective MAS tool suitable for a wide range of plant breeding programs (He et al., 2014). Gene editing technologies, particularly the CRISPR/Cas9 system, offer revolutionary improvements in cassava breeding. By precisely modifying the DNA sequence of specific genes, these techniques allow scientists to introduce or correct genetic variants directly into the cassava genome, thereby improving the performance of specific agronomic traits. Dheer et al. (2020) mentioned that gene editing technology has been used to develop cassava varieties with improved disease resistance and enhanced nutritional quality. In addition, transgenic techniques, such as the use of Agrobacterium mediated transformation systems, have also been used to introduce foreign genes into cassava to produce new traits, such as improved starch quality and insect resistance. 5 Current Cassava Improvement Strategies and Progress 5.1 Combination of traditional breeding and modern biotechnology In the current cassava improvement strategy, the combination of traditional breeding methods and modern biotechnology is particularly important. By integrating traditional selection with molecular marker-assisted selection (MAS), gene editing, and other biotechnologies, breeders are able to produce new varieties with high yields, high quality, and good stress resistance. For example, the International Centre for Tropical Agriculture (CIAT) has significantly increased cassava yields and dry matter content over the past few decades by working with international and national projects, supported by biological and social factors. This integrated breeding strategy has enabled many countries to develop improved varieties adapted to local conditions.
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