Epistasis in the Expression of Relevant Traits in Cassava (Manihot esculenta Crantz) for Subhumid Conditions

Abstract

There is limited knowledge on the inheritance of agronomic traits in cassava and the importance of epistasis for most crops. A nine-parent diallel study was conducted in subhumid environments. Thirty clones were obtained from each F1 cross. Each clone was represented by six plants, which were distributed in three replications at two locations. Therefore the same 30 genotypes of each F1 cross were planted in the three replications at the two locations. Analysis of variance suggested significant genetic effects for all variables analyzed (reaction to thrips, fresh root and foliage yields, harvest index, dry matter content, and root dry matter yield). Significant epistatic effects were observed for all variables, except harvest index. Dominance variance was always significant, except for dry matter content and dry matter yield. Additive variance was significant only for reaction to thrips. Results suggested that dominance plays an important role in complex traits such as root yield. The significance of epistasis can help us understand the difficulties of quantitative genetics models and QTLs in satisfactorily explaining phenotypic variation in traits with complex inheritance. Significant epistasis would justify the production of inbred parental lines to fix favorable allele combinations in the production of hybrid cassava cultivars.

Marker-based estimates reveal significant non-additive effects in clonally propagated cassava (Manihot esculenta): implications for the prediction of total genetic value and the selection of varieties

“…These findings confirm the conclusions of numerous diallelic studies conducted with both Latin American (Cach et al 2005(Cach et al , 2006Calle et al 2005;Jaramillo et al 2005;Pérez et al 2005a,b) and African cassava (Zacarias and Labuschagne 2010;Kulembeka et al 2012;Tumuhimbise et al 2014;Chalwe et al 2015) germplasm (see also Ceballos et al 2015). In agreement with the findings of Ly et al (2013), we found cassava mosaic disease severity (MCMDS) to be well predicted with an additive only model.…”

“…We then assessed the accuracy of genomic prediction of additive compared to total (additive plus nonadditive) genetic value. Using several approaches and datasets based on genome-wide marker data, we confirmed previous findings in cassava based on diallel crosses nonadditive genetic variation is significant, especially for yield traits (Cach et al 2005(Cach et al , 2006Calle et al 2005;Jaramillo et al 2005;Pérez et al 2005a,b;Zacarias and Labuschagne 2010;Kulembeka et al 2012;Tumuhimbise et al 2014;Ceballos et al 2015;Chalwe et al 2015). A potential weakness of the marker system we used (GBS) is that it generates a high proportion of missing marker data and it may undercall heterozygotes when read depth is insufficient.…”

“…Diallelic studies in cassava indicate that nonadditive genetic effects (e.g., specific combining ability) are strong, particularly for root yield traits (Cach et al 2005(Cach et al , 2006Calle et al 2005;Jaramillo et al 2005;Pérez et al 2005a,b;Zacarias and Labuschagne 2010;Kulembeka et al 2012;Tumuhimbise et al 2014;Ceballos et al 2015;Chalwe et al 2015). If the limited number of parents tested thus far represents the broader cassava breeding germplasm, genetic gains, especially for already lowheritability root yield traits, will be slow regardless of the breeding scheme employed (e.g., phenotypic vs. pedigree vs. genomic selection).…”

Cassava traits and end-user preference: Relating traits to consumer liking, sensory perception, and genetics

“…using genetic engineering or conventional breeding) has to be watched closely because modifications in a particular trait might have impact on other characteristics of the roots (epistasis). Cach et al, 2005 reported that there is paucity of knowledge on the inheritance of agronomic traits in cassava and the importance of epistasis. It however appears that epistasis is very likely to occur for non-negligible number of traits in cassava.…”

Breeding Open-Pollinated, Hybrid and Transgenic Outcrossing Species

“…Dominance and epistasis are significant for fresh root and foliage yields . A significant epistasis may explain the difficulty of quantitative genetic models and QTL for accounting phenotypic variation of cassava traits with complex inheritance (Cach et al 2005). Prediction accuracy must improve for genomic selection to outperform phenotypic selection on a per-year basis, for example, by increasing training population size or becoming less dependent on historical datasets (Ly et al 2013).…”