Ogbonna AC, Braatz de Andrade LR, Rabbi IY, Mueller LA, Jorge de Oliveira E, Bauchet

GJ. Plant J. 2021 Feb; 105(3):754-770. doi: 10.1111/tpj.15071

Abstract

Manihot esculenta (cassava) is a root crop originating from South America that is a major staple in the tropics, including in marginal environments. This study focused on South American and African germplasm and investigated the genetic architecture of hydrogen cyanide (HCN), a major component of root quality. HCN, representing total cyanogenic glucosides, is a plant defense component against herbivory but is also toxic for human consumption. We genotyped 3354 landraces and modern breeding lines originating from 26 Brazilian states and 1389 individuals were phenotypically characterized across multi-year trials for HCN. All plant material was subjected to high-density genotyping using genotyping by sequencing. We performed genome-wide association mapping to characterize the genetic architecture and gene mapping of HCN. Field experiments revealed strong broad- and narrow-sense trait heritability (0.82 and 0.41, respectively). Two major loci were identified, encoding for an ATPase and a MATE protein, and contributing up to 7 and 30% of the HCN concentration in roots, respectively. We developed diagnostic markers for breeding applications, validated trait architecture consistency in African germplasm and investigated further evidence for the domestication of sweet and bitter cassava. Fine genomic characterization revealed: (i) the major role played by vacuolar transporters in regulating HCN content; (ii) the co-domestication of sweet and bitter cassava major alleles are dependent upon geographical zone; and (iii) the major loci allele for high HCN in M. esculenta Crantz seems to originate from its ancestor, M. esculenta subsp. flabellifolia. Taken together, these findings expand our insights into cyanogenic glucosides in cassava roots and its glycosylated derivatives in plants.

See https://pubmed.ncbi.nlm.nih.gov/33164279/

Figure 5

Manhattan plot from a mixed linear model (MLM‐LOCO) with the chromosome on which the candidate SNP is located excluded from calculating the genetic relationship matrix (GRM). The MLM‐LOCO summarizes the genome‐wide association results for HCN in Latin American (LA, Brazilian), African (AF), joint Latin American + African (LA + AF) and unique Latin American (UNIQUE LA) germplasms. Bonferroni significance threshold is shown in red. A quantile–quantile plot is inserted to demonstrate the observed and expected −log₁₀ P for HCN.