Cry1Ac insecticidal protein levels in genetically modified Coffea canephora Pierre coffee plants were negatively correlated with the growth speed in a field experiment

Abstract

Genetically-modified coffee clones (GMCs) were presented in a previous work. They were created from a single commercial clone of Coffea canephora Pierre (clone 126). Therefore they all have the same genotype, except for the localization of the transgenic insertions. They synthesize the Bacillus thuringiensis endotoxin Cry1Ac against Leucoptera coffeella Guerin-Meneville, a secondary pest of C. canephora and one of the main pest of C. arabica in South America. The synthetic Cry1Ac gene is regulated by the EF1α-A1 promoter of Arabidopsis thaliana (L.) Heynh. They were tested in an experimental field for their resistance against the pest insect in a previous work. In the present work, levels of Cry1Ac were measured in the leaves. The insecticidal protein was evenly distributed in all the leaves. Cry1Ac levels were measured once in the coffee plants of a sensitive GMC and of 14 resistant ones grown in the experimental field and in plants grown in a greenhouse. Some resistant GMCs contained higher levels but it is not possible to confirm that it would be enough for a sustainable resistance to the pest. Growth speed was variable in the plot. The correlation with plant height and other indicators of plant growth was examined. Cry1Ac levels in the GMCs were negatively correlated with growth speed. The latter was not statistically influenced neither by Cry1Ac synthesis nor by the genetic modification in itself as seen by comparing the GMCs and the unmodified control clone 126. Hence the conclusion is that the growth conferred to field-grown plants by environmental factors and especially the soil was probably the underlying cause of the negative correlation. Other field experiments would be necessary in order to confirm this result. It would be important that the genetic construct inserted in these GMCs and mainly the EF1α-A1 promoter of the Cry1Ac gene be reconsidered since Cry1Ac levels might be too low to provide efficient and sustainable protection against L. coffeella in a highly favourable environment for coffee plants. Alternatives are discussed.