Molecular-assisted selection for resistance to cassava mosaic disease in Manihot esculenta Crantz

Abstract

The geminivirus complex known as cassava mosaic disease (CMD) is one of the most devastating viruses for cassava (Manihot esculenta Crantz). The aim of this study was to use molecular-assisted selection (MAS) to identify CMD-resistant accessions and ascertain promising crosses with elite Brazilian varieties. One thousand two hundred twenty-four accessions were genotyped using five molecular markers (NS169, NS158, SSRY028, SSRY040 and RME1) that were associated with resistance to CMD, along with 402 SNPs (single-nucleotide polymorphism). The promising crosses were identified using a discriminant analysis of main component (DAPC), and the matrix of genomic relationship was estimated with SNP markers. The CMD1 gene, previously described in M. glaziovii, was not found in M. esculenta. In contrast, the CMD2 gene was found in 5, 4 and 5 % of cassava accessions, with flanking markers NS169+RME1, NS158+RME1 and SSRY28+RME1, respectively. Only seven accessions presented all markers linked to the CMD resistance. The DAPC of the seven accessions along with 17 elite cassava varieties led to the formation of three divergent clusters. Potential sources of resistance to CMD were divided into two groups, while the elite varieties were distributed into three groups. The low estimates of the genomic relationship (ranging from -0.167 to 0.681 with an average of 0.076) contributed to the success in identifying contrasting genotypes. The use of MAS in countries where CMD is a quarantine disease constitutes a successful strategy not only for identifying the resistant accessions but also for determining the promising crosses.

Marker-assisted selection complements phenotypic screening at seedling stage to identify cassava mosaic disease-resistant genotypes in African cassava populations

“…Six molecular markers (Table 2 ) associated with the CMD2 gene used in previous studies 22 – 24 , 30 , 31 were selected to screen the cassava genotypes for CMD resistance. Multiplex PCRs were run after determining the working annealing temperature which ranged from 50 to 65 °C for each primer using gradient PCR.…”

Technological Innovations for Improving Cassava Production in Sub-Saharan Africa

“…Markers tightly associated with CMD2 have been effectively used to identify genotypes bearing the CMD2 gene in West African germplasm, introgression of CMD2 genes into various cassava germplasm, and selection of parental lines for planned crosses. This has enabled breeders to focus on fewer genotypes at an early stage of the breeding program, saving the breeder time and labor cost ( Blair et al, 2007 ; Okogbenin et al, 2012 ; do Carmo et al, 2015 ). MAS is appropriate for moderate to highly inherited traits that are controlled by a few major genes and not sufficiently predictive for quantitatively inherited traits controlled by many genes at different loci, each contribution to a small effect of the phenotypic expression ( Singh et al, 2019 ).…”

Molecular marker assisted selection for increasing inbreeding in S1 populations of cassava

“…This technique has been used for several purposes, such as assisted backcrossing, quantitative trait loci (QTL) mapping, heterosis studies Mackill 2008, Kobayashi et al 2013) and for identifying individuals with a higher homozygosity level in segregating populations (Oliveira et al 2010(Oliveira et al , 2012b. In cassava, the most successful application of MAS has been in the selection for resistance to cassava mosaic virus (CMD) (Okogbenin et al 2007, Carmo et al 2015.…”