Ecological impact of GM crops: Time for a sober scientific assessment

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Ecological impact of GM crops: Time for a sober scientific assessment

Wynand J. van der Walt

Wynand van der Walt explores the risk of GMO's, the risks of not adopting new technology and also providing opinion on fears of super pests, super weeds, impact of GMO's on biodiversity and more.

Natural ecosystems were disturbed on the day some 11000 years ago that the first planet dwellers decided to dig holes in the ground and plant seeds and tubers. Today the planet has to cope with over 6 billion people and urbanization, industrialization, abject poverty, while agricultural practices continue to impact on the environment. Assessing impact on the environment is much more than just a tunnel vision approach on hypothetical risks of GM crops. South Africa's existing problems relate to the listed 117 major invader species and another 84 new invaders. We should all agree that approval of GM and new conventional varieties with potential risk should be subject to prior assessment for adverse impact on the environment. Identifying problems pro-actively is substantially better than corrective action after the problem has surfaced.

It seems that there is inadequate capacity at local government level and this is precisely where the environmental management legislation could fail. Delegation and fragmentation of responsibilities to provinces and local authorities run the risk of inadequate capacity, funding or awareness. Obvious examples include bugweed (Solanum) lining the road shoulders around Pretoria, liberally blended with a vast array of farm weeds, or pink pom-pom (Campuloclinium) now having invaded thousands of hectares all over Gauteng, including nature reserves, or billions of new black wattle plants having taken the place of trees chopped down. The primary factor for roadside invasion is mowing of grass only once per year when weeds have set seed, serving as a massive redistribution system. Baling of grass cuttings for hay will transfer the roadside problem to the farm. This picture conveys the message that local government continues to add to the problem while central government is forking out billions in control measures. In contrast, the GMO Act regulates at national level and consensus decision making involves six government departments which includes environmental legislation, prior to release of new GM varieties.

Genetic changes in plants, animals and micro-organisms have taken place with increasing impact and are as old as agricultural practices itself, as farmers domesticated and selected biodiversity. South Africa grows some 100 000 hectares of triticale, a wheat-rye cross, and consumers can enjoy plumcots, pluots and apriums from apricot-plum crosses, all coming from non-genetic modification techniques. Vegetative propagation through budding, grafting, tubers, rootstocks and tissue culture are major industries.

Genetic modification (GM) application only started when scientists began to understand the periodic jump of genes from their positions on one chromosome to other positions in the genome (transposons), micro-organisms being able to incorporate foreign naked DNA (transformation) and vectors carrying genes from one species to another (transduction). The first applications of GM technology were in human health (insulin in 1982), food processing (chymosin enzyme), industrial production, and, only by the early 1990s, GM crop plants.

Assessing the risk

Firstly, we need to understand what "risk" is all about. The identification of risk starts with considering hypothetical scenarios based on past experience, i.e., the "what if" approach. Identifying a potential risk is next, followed by the probability that the risk will happen, and by analyzing the potential consequences of such an event. It is good to remember that consequence do not equal damage. Next is developing risk management systems. Most risk approaches stop here and do not go to the next steps, namely, can regulatory systems be practical, implementable and affordable, or will it stifle progress and innovation? Consider the regulation of risk versus the risk of regulation. The comparator must always be the baseline of what we already have (e.g., conventional crops), as well as the risk of not adopting a specific new technology. Approval by authorities of new technologies should be based on precaution. This presents an opportunity to make a decision in the absence of scientific certainty, and such a decision could be approval, delay until further information become available, or rejection.

In dealing with new plant species or new varieties, GM or conventional, risk analysis requires botanical information: dispersal of pollen, seeds or vegetative parts, and the frequency thereof. If the chance of these is zero, then the risks of invasiveness are zero. The nature and action of the gene has to be described. Without such information, sweeping statements like genes jumping into nature, horizontal gene flow and crosspollination, are meaningless.

The typical concerns about potential adverse impact of GM crops on natural ecosystems can be considered as follows:

Will GM crops invade nature?

Domesticated food crops have had weediness tendencies bred out of their genetic make-up. To date there is no evidence that major food crops, GM or conventional, have become invasive, as shown by extensive investigations, as well as experience gained from a cumulative area of over 300 million hectares of GM crops grown since 1996. There exists no evidence that insertion of a gene for herbicide tolerance or disease resistance can alter the inherent lack of invasiveness. Nevertheless, it is advisable that GM crops are assessed on a case-by-case basis prior to approval for trial or commercial release.

Will GM crops outcross with wild species?

A range of natural genetic and physiological barriers exists to prevent this. For successful out-crossing, the donor GM plant has to have fertile pollen that can spread, the recipient wild species has to be fertilized and produce viable seed that will germinate to give fertile hybrid plants that can maintain reproduction. Without these conditions being met, there cannot be out-crossing risks to wild species. No evidence has been produced to date to show that GM plants are different in this respect from conventional. GM maize, soyabean and cotton grown in South Africa have no related wild species here with which they can cross.

Horizontal gene flow

The technical definition refers to the transfer of genes from a donor species to recipient species with which it is not sexually compatible, with specific reference to transfer between plants and micro-organisms. Such gene flow occurs naturally between bacteria, and the transfer via Agrobacterium to plants is well documented. DNA is digested and destroyed very rapidly. For gene transfer from plants to bacteria, the intact gene has to be in the form of free DNA, be made available to the bacterium, taken up and stably integrated by the recipient bacterium so that it can be functional to express the unique trait. This can only happen when the DNA of the gene and the bacterium have sequence homology. Extensive investigations have failed to detect such a mechanism of gene transfer in crop plants.

A repeated concern deals with the risk of the antibiotic resistance marker genes being transferred to gut or soil bacteria. Detailed assessments have been carried out with the nptII kanamycin resistance gene. Natural resistance to kanamycin has been widespread in both soil and intestinal bacteria long before arrival of GM crops. However, as a precautionary measure, biotech companies are moving away from using antibiotic resistance genes as markers.

What about secondary ecological impact?

As regards non-target soil micro-organisms, one can only refer to extensive studies that could not detect any changes in the microbial population in the rhizosphere region around plant roots between GM and conventional plants.

Will super pests and weeds arise?

Conventional plant breeding for resistance showed that pests are likely to develop resistance under conditions of high selection pressure. The protein from Bt, turned into a toxin by Lepidoptera larvae, actually has a 40-year track record of persistent efficacy as a spray-on natural bio-insecticide. The genetic solution to minimizing this risk is multifold: using different Bt genes, having a conventional crop as refuge, alternating crops and varieties, varieties with more than one Bt gene, and breeding multiline resistance using GM and conventional systems.

Long term use of herbicides on conventional crops has resulted in some weeds acquiring degrees of tolerance. The same could be expected with over-application of herbicides to which GM crops are tolerant and needs to be managed, e.g. using different herbicide tolerant systems.

Impact on biodiversity

Biodiversity describes the variability within species, between species and in ecosystems. Commercial agriculture has narrowed the genetic base of food crops in some countries. South Africa has had the benefit of having developed most of its own commercial varieties from local and international germplasm, as well as having had access to imported varieties from all continents. Farmers now have a choice of over 3000 plant varieties, more than ever before. Therefore, food crop biodiversity has continued to increase and GM varieties offer additional choices. Farmers are offered a choice. No one is forced to buy GM seed.

Can GM crops affect purity of other crops?

The co-existence of various types of maize has been with us for over 100 years: white and yellow maize, popcorn (a snack food), sweetcorn (a vegetable), and special starch types for industrial use. Many countries produce both edible and industrial starch potatoes, as well as industrial and canola oilseed rape. All of these have been managed by way of separate production, handling and marketing. The advent of GM brings another dimension to this equation. The EU has accepted co-existence of GM, organic and non-GM production systems. South Africa is completing identity preservation systems for GM and non-GM crops. There are two sides to this concern: presence of GM in non-GM or organic products, and presence of non-GM or organic in GM products. What is good for the sauce is good for the gander.

The risk of not adopting new technologies

Improved seed and advanced plant varieties, in combination with improved farm management systems, fertilizers and crop protection chemicals, have increased South African crop yields per hectare five-fold since 1950 for both maize and wheat. Without this, we would have required 14 million hectares to produce this year's maize crop and 4 million for wheat; a mission impossible. The multi-billion Rand fresh produce export industry would have collapsed long ago without modern varieties, management and quality control systems.

The adverse effects of not adopting GM crops need to be assessed. Here are the proven benefits:
· Increased productivity that will reduce pressure on converting forests, wetlands and marginal areas to farming
· Improved net income, especially for small-scale farmers
· Significant reduction of some 60-80% in insecticide use
· Replacing herbicides having persistence in soils and soil water with more environmentally friendly ones
· Facilitating minimum tillage practices that promote mulch and reduce erosion
· Facilitating crop rotation
· Reducing farm worker exposure to insecticides
· Reducing risk of pesticide residues in food products in the face of very strict export market regulations on residues
· Using crops like Bt maize to reduce risk of mycotoxins with known carcinogenic and toxic effects on humans and animals, and helping to comply with strict international standards on mycotoxin presence.
· Using herbicide tolerant crops to reduce risk of weed damage to crops and weed spread into nature.
· Canola and soybean with improved oil qualities to benefit human health
· Perishable fresh produce with longer shelf life.
· Precluding spread of potentially invasive plants can be achieved by conventional and GM technologies to render the pollen or the seeds from crosspollination sterile, as had been done over 20 years ago with sterile lantana.
· Using GMOs for bio-remediation, as well as to reduce industrial contamination and waste.

Can organic replace GM and conventional production?

Organic systems endeavour to eliminate synthetic pesticides and fertilizers, while improving organic content and soil status. An extensive body of scientific data shows that production efficiency is 20-30% less that of the conventional. Organic production could be supported if it benefits the environment over the long term and if farmers obtain sufficient premium to make it economically feasible. What is needed are environmental impact assessments of the effect of ongoing use of neem extract, tobacco extract, Bt spores or toxin, pyrethrum, rotenone (carcinogenic to rats), and mineral oils as insecticides; lecithin, sulphur and copper salts as fungicides; and farmyard manure, urine slurry, and processed animal products as fertilizers. There is no voluntary or regulatory requirement for ecosystem impact studies prior to use, as for GM crops.

In conclusion

The present serious damage to biodiversity comes from conventional invasive species like woody species, lantana, bugweed and pompom. However, primary threats to biodiversity and ecosystems are population pressure, sprawling urbanization, industrialization, uncontrolled commercial harvesting of indigenous plants (an annual R3 billion industry), and inadequate law enforcement.

Recognition should be given to the beneficial role that breeding of improved varieties and GM technology has and is playing in food production efficiency and security, with concomitant benefits to society and the environment. Credit is due to government for efforts to address invasive plants and water quality and especially to the body of dedicated scientists involved in relevant research and application. Efficient enforcement at local grassroots level of increasingly complex environmental legislation remains a serious cause of concern.

Assessing environmental impact of new GM varieties prior to approval for release is to be supported, subject to decisions being science-based. The same concerns are applicable to certain new conventional and ornamental species and alternate farming systems. The endless polarized debate on GM can be short-circuited by having comparative GM, conventional and organic side-by-side impact studies on environment done by a group of credible independent scientists. In the meantime efforts to manipulate concerns about hypothetical GM risks into impending disasters should be exposed for what they are: scare-mongering.

More information:

Wynand J. van der Walt is a consultant in agricultural biotechnology. wynandjvdw@telkomsa.net

NOTE
The views expressed in this review are those of the author and may not necessarily reflect the views of Science in Africa magazine nor people consulted in the preparation of this article.

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