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Bt Crops and Soil Biota

In an Aug. 19, 2020 DTN article titled “Bt Bean Targets SCN”, author Emily Unglesbee announces that the US-EPA has granted BASF a registration for a Bt soybean trait (currently known as GMB151) that will target the soybean cyst nematode (SCN). This trait is presently registered for use as a breeding material only; thus, it is still years away from potential commercialization. The registration application for this trait can be found here.

This is a promising development for the soybean industry because of SCN’s increasing ability to infest soybean varieties that have the predominant resistance trait derived from PI 88788. The BASF trait expresses a new novel Bt protein Cry14Ab-1, which damages the gut of the SCN when they ingest it. It appears to have no activity on any other soybean pest species, or on non-target organisms. This new trait is intended to be bred into soybean varieties that already possess resistance traits derived from PI 88788 and Peking in order to enhance overall SCN management, and will result in the first Bt soybean varieties brought to the U.S. market.

The development and use of Bt crops (particularly corn and cotton) has created a debate about their effects on the micro-environment in which they are grown. Of particular interest is their effect on non-target soil invertebrates that are recognized for their contributions to the availability of nutrients to plants, their activity on soil organic matter, and their overall enhancement of soil health properties. Thus, it is particularly relevant that these organisms are protected when Bt crops are grown on soils that they inhabit. This effect was analyzed in an article titled “The effect of Bt crops on soil invertebrates: a systematic review and quantitative meta-analysis” that is authored by Krogh, Kostov, and Damgaard and published in the journal Transgenic Research (https://doi.org/10.1007/s11248-020-00213-y). Major points from the article follow.

•   To provide protection against certain crop pests, crop breeders have developed transgenic Bt-crops that have been genetically modified by inserting a gene from Bacillus thuriengensis (a naturally-occurring soil bacterium) into the modified plant’s genome so that it expresses a Cry protein that is toxic to a targeted pest organism.

•   Soil invertebrates are exposed to field-grown Bt crops in the soil rhizosphere through roots and their exudates, and organic matter resulting from those crops. There is an ongoing debate about the ecological effects of these Bt crops on these soil invertebrates because of their soil exposure when Bt crops are grown.

•   The results presented in the above study analyze the effect of Bt crops (types Cry1Ab, Cry1Ac, Cry3Bb1, and Cry3Aa) on soil invertebrates that include Protista (primarily microscopic unicellular organisms), nematodes, Collembola (springtails and allies that are decomposers), mites, enchytraeids (miniature version of an earthworm), and earthworms in soil where these crops are grown compared to those populations in soil where non-Bt or conventional crops are grown.

•   Results from 22 field studies conducted across a range of environmental conditions (36 locations in 10 countries) were selected and used in the meta-analysis to quantify the effect of Bt crops on soil invertebrates. Corn and cotton were the crops used in a large majority of the studies.

•   This meta-analysis did not find any significant effects of field-grown Bt crops on non-target soil invertebrates.

The results of this meta-analysis indicate that current genetically modified Bt crops have no impact on soil invertebrates. Even though the above-mentioned Bt trait that is forthcoming in soybean for activity against SCN expresses a new Bt protein not included in the above study, the results cited above indicate that it is not likely to adversely affect non-target microbes and invertebrates in the soil. This is certainly an encouraging point for the development of this new Bt trait in soybean.

Composed by Larry G. Heatherly, Sept. 2020, larryheatherly@bellsouth.net