Compositional differences between near‐isogenic GM and conventional maize hybrids are associated with backcrossing practices in conventional breeding

Abstract

SummaryHere, we show that differences between genetically modified (GM) and non-GM comparators cannot be attributed unequivocally to the GM trait, but arise because of minor genomic differences in near-isogenic lines. Specifically, this study contrasted the effect of three GM traits (drought tolerance, MON 87460; herbicide resistance, NK603; insect protection, MON 89034) on maize grain composition relative to the effects of residual genetic variation from backcrossing. Important features of the study included (i) marker-assisted backcrossing to generate genetically similar inbred variants for each GM line, (ii) high-resolution genotyping to evaluate the genetic similarity of GM lines to the corresponding recurrent parents and (iii) introgression of the different GM traits separately into a wide range of genetically distinct conventional inbred lines. The F1 hybrids of all lines were grown concurrently at three replicated field sites in the United States during the 2012 growing season, and harvested grain was subjected to compositional analysis. Proximates (protein, starch and oil), amino acids, fatty acids, tocopherols and minerals were measured. The number of statistically significant differences (a = 0.05), as well as magnitudes of difference, in mean levels of these components between corresponding GM variants was essentially identical to that between GM and non-GM controls. The largest sources of compositional variation were the genetic background of the different conventional inbred lines (males and females) used to generate the maize hybrids and location. The lack of any compositional effect attributable to GM suggests the development of modern agricultural biotechnology has been accompanied by a lack of any safety or nutritional concerns.

Evolution of risk assessment strategies for food and feed uses of stacked GM events

“…The observed variability in grain composition can be attributed to these differences. It is well documented that both growing environment and germplasm have a strong influence on the composition of maize (Harrigan et al ., ; Reynolds et al ., ; Skogerson et al ., ; Venkatesh et al ., ). These results are consistent with the expectation that these events have little effect on composition, whether as single events or stacked with one another, and are a good representation of the variability in composition inherent in maize.…”

Bringing New Plant Varieties to Market: Plant Breeding and Selection Practices Advance Beneficial Characteristics while Minimizing Unintended Changes

“…This study showed that genetic changes accumulated spontaneously across many conventional germplasm (i.e., standing variation). Another recent study of many maize varieties (both conventional and GM) showed that most of the observed compositional differences were associated with the backcrossing practices from conventional breeding (Venkatesh et al, 2015). Repetitive DNA sequences and structural variations in plants have the potential to contribute to genetic change.…”

“…As a result, extensive regulatory requirements for GM crops, which use a comparative safety assessment process, are now in place (König et al, 2004;Cellini et al, 2004;EFSA, 2006;Paoletti et al, 2008;CODEX, 2009;Privalle et al, 2012;Hoekenga et al, 2013;Prado et al, 2014). Since that time, numerous studies have found that GM varieties are compositionally equivalent to conventional crops Herman and Price, 2013;Hoekenga et al, 2013;Ricroch, 2013;Xu et al, 2014;Ladics et al, 2015aLadics et al, , 2015bCurran et al, 2015;Venkatesh et al, 2015Venkatesh et al, , 2016. The exceptions are a few cases where the desired trait confers an intended change in composition, such as improved nutrition (Chassy et al, 2008).…”

Genetic diversity among plants of non-transgenic and transgenic versions of a single cross maize hybrid

“…This result suggests that parental lines could have presented residual heterozygosis for these loci due to multiple conventional breeding steps rather than to the transgene introduction (Harrigan et al, 2010;Venkatesh et al, 2014). Moreover, the Bt-RR version (DK747MGRR) exhibited the lowest genetic diversity value despite the fact that both, the MON810 event and the NK603 event, were independently inserted in the maize genome and stacked by backcrossing (CERA, 2012).…”