Literature lacks to confront our results about the purity of Bt-cotton seeds. There should be data resulting from control by seed production organizations but they are not disclosed. The reality of lack of seed purity is documented only in a few countries.
In Pakistan, the lack of seed purity for both conventional and Bt cotton has been assessed through a research work confronting farmers' declaration on the type of seeds they used and the biochemical control of plant leaves. It was found that only a single-Bt gene cotton was cultivated (Cry1Ac) and 11% of farmers believed they were cultivating Bt cotton while the Bt gene was not present, and 5% of farmers believed they were cultivating non-Bt cotton when, in fact, the Bt gene was present (Spielman et al 2017). The figures of discrepancies in our study are higher; the fact that a double Bt gene cotton was used should be an explaining factor, although the authenticity of the seeds supplied only by the cotton company should be better.
In China, through the measurement of Bt toxin contents, Pemsl, Waibel, and Gutierrez (2005) have suspected the lack of seed purity in Bt cotton varieties released in a very competitive context. Besides, in the particular case of hybrid varieties destined firstly for cultivation in more southern province of China, the lack of seed purity was also addressed indirectly through the assessment of Bt toxins (Xu et al. 2008). In both cases, the extent of purity imperfection was not estimated.
In Burkina Faso, the control of Bt nature of FK95 BG2 variety is implemented but data were not accessible. The only information available was obtained in an external initiative to check the Bt status of cotton plants in claimed Bt-cotton fields in this country. Out of the tests implemented on 45 samples, 24.4% of samples had no Bt status at all, 17.8% had a single Bt gene status equally distributed between the two Bt genes, and 57.8% had the double Bt gene status (Michel Fok et al. 2016). These figures are quite consistent with those in our present study that is based on a much higher number of samples.
More literature deal with the phenomenon of contamination of conventional seeds by Bt genes, but with much less, if any, quantitative assessment than in our study. The issue is more documented mainly because the phenomenon has endangered the continuation of organic cotton production, notably in the USA (Hershaw 2013) where it is claimed that no organic cotton producer could be meeting the purity criterion of conventional feature. The contamination status has become so much generalized and unescapable that Endres (2005) advocates a revision of federal and states laws governing seed purity. In India, in almost 30% of cases examined, conventional seeds supplied for refuge purpose contained Bt genes (S. Kranthi et al. 2017) although at non-specified extent. In Burkina Faso, a study mandated by promoters of organic cotton production pointed out that about 50% of organic cotton producers were provided with seeds containing Bt genes, however with the stringent criterion that Bt presence was declared when found on at least one out of 300 seeds and tests completed with lateral flow strips (Vognan and Bourgou 2014).
Our results clearly show that, at the eve of suspending the use of Bt-cotton, conventional seeds were contaminated at large extent. As we have retained rather conservative threshold of the presence of Bt genes in conventional seeds, the real situation of contamination was indeed worse than indicated in our figures.
The main reason of the observed contamination should be the lack of specific attention to prevent contamination when Bt-cotton was disseminated at large scale. No specific measures were implemented to delineate non-Bt cotton zone where conventional seed production could have taken place. In addition, one may suspect some arrangements between farmers in exchanging seeds, including in seed production area, so that some assumed conventional cotton fields were indeed Bt-cotton ones. The reverse case was also possible as there were farmers unwilling to grow Bt-cotton, particularly at the first years of the shift to this cotton type. Quality control with regard to the Bt traits in seed processing was quantitatively insufficient as it can be observed through the procedures of implementation of ELISA tests (Sofitex n.d.). In addition, these tests were conducted mainly to check the Bt nature and not the level of presence of Bt genes.
Since the suspension of Bt-cotton use in 2016, it is probable that the seed contamination of conventional cotton by Bt genes has not persisted at the quite high level found in our study, but it is hard to claim that Bt genes have totally disappeared from fields. After the suspension decision, seed control was implemented with measures that were more stringent. Burkina Faso also has shifted to using another conventional variety. This variety shift could nevertheless not be total in one campaign. There must remain some level of adventitious and unintentional presence of Bt genes in cotton fields. So, to some extent, cotton producers keep benefitting from some effectiveness of Bt genes to control targeted pests.
At the eve of the suspension of Bt cotton use, the GM nature of the Bt-cotton seeds could be acknowledged although it was not perfect. Our point is based on ELISA test indicating that Bt toxins were detected but not at the levels expected. The inference to the absence of Bt genes might be excessive −because of various factors impacting on the expression of Bt genes (Huang et al. 2014; Iqbal et al. 2013; Rochester 2006; Wan et al. 2005)− but this argument little applies in our study as we observed this expression in falsely-assumed conventional seeds in the same growing conditions.
Our work is the first to quantify the loss of the BG2 status up to a poor level. The BG2 status (based on the double presence of Cry1Ac and Cry2Ab genes) was applicable only to 40% of the seeds supplied. Again, because of the conservative threshold retained for purity with regard to the presence of Bt genes in seeds, the real lack of BG2 status was even worse than indicated by our figures.
Two factors at least are beneath the observed lack of Bt purity in seeds. Because of the insufficient control of the BG2 status at the stage of seed production and processing, the lack of the adjustment of the seed production scheme is to blame. However, as the seeds for large scale release were provided by Monsanto in a very short delay (Bourgou et al., 2020; Fok, 2016), too short for stabilized and homogenous seeds (technically impossible to achieve in two years with at most four cycles), another factor of purity shortfalls dates back to the seeds originally supplied. The original lack of seed purity would have made ulterior quality control more difficult and costly, so this lack −not reported so far in other countries− could be regarded as the principal factor of the poor BG2 status of the Bt-cotton seeds.
The cultivation of Bt-cotton with defaulting purity of its seeds has worrisome implications with regard to the effectiveness and sustainability of the related Bt genes against target pests. A mixture of four cotton types −with regard to the presence of Bt genes (none, only Cry1Ac or Cry2Ab and both Bt genes)− implies disadvantages additional to those indicated in introduction and wipes out the rationale of having opted for stacked genes. The presence of single Bt gene has helped the emergence of resistance to single gene, hence facilitating the emergence of resistance to double Bt genes. It is likely that the process of resistance build-up against the two Bt genes had already started and that resistant alleles could already be encountered, at least at low frequencies. If so, the relaunch of Bt-cotton with the same genes in Burkina Faso would not be ensured of a lasting effectiveness, regardless of the risk of outbreak of secondary pests encountered in most (if not all) countries having adopted Bt-cotton long enough (Zhao, Ho, and Azadi 2011; B. K. Kranthi 2011; M. Fok 2010).