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Helping Plants to Help Themselves - 27/07/2010
 

There's More to the Rhizosphere than Nitrogen Fixation (FAO)


1. The Food and Agriculture Organization predicts that by 2050 global food production needs to increase by 70% (assuming that extensive changes in consumption in some regions and reduction of wastage can be achieved, as well as reduced growth of human populations and demands for the increasing longevity can be met; redistributions must also be taken into account, especially drifts of population towards concentrations in cities and slums). "We must reduce crop yield losses in new, sustainable ways," observes Dr Toby Bruce from Rothamsted Research (an institute of the BBSRC), emphasizing the consequent needs to overcome pestilence. As an alternative to agrochemicals, natural plant defences could be induced with activators. Tony Bruce predicts that "natural plant immunity is likely to become more important in the future; this is an approach which exploits natural chemicals as treatments to modulate defence responses." It is also an approach that obviates delays and doubts over resort to GM technology; however, objections to these methods seem to be exciting less complaint by opponents than they were raising only a few years ago to "Frankenstein" foods, which are becoming widely in important areas such as India and China.

2. The non-GM ploy goes like this: signals released by damaged plants activate the defence mechanisms of neighboring plants and make them more resistant to an impending insect attack. Such signals could be used as alternative treatments to replace synthetic insecticides that could then be reserved for particularly bad pest infestations. Furthermore, by encouraging natural enemies of pests, plant activators are compatible with integrated pest management systems. In 2009 the European review of pesticide approval passed a new directive, which reduced the number of active ingredients authorized for use in pesticides. Scientists predict that this could ultimately reduce productivity. The new directive will necessitate finding new ways to minimize crop losses due to insect pests. It seems that Dr Bruce has in mind systems in plants where specified acquired resistance may result - like the immune system and responses in animals - to build protection against harm caused by invasion and penetration of first lines of defence (which could be shells, skins, waxes, and bitter or toxic principles to deter predators.) Such deterrents (phytoalexins) include substances such as salicylates and other chemicals that have been turned to account in the development of herbals and medicines in the treatments of animals of all kinds, including humans.

3. However, Toby Bruce has in mind also certain host-parasite interactions in which the invader is stimulated by emissions of exudates from germinating seeds to provoke attack by pests prompted thereby to attack their hosts before the damage underground to the host's roots are obvious. The hatching and damage resulting in the rhizosphere from such attacks is exemplified by the damage wrought by the hatching of cysts of the potato eelworm cysts. Crops in Africa of certain cereals such as sorghum and millet have been ruined in this way by exudates from the roots of a parasite weed called Striga (witchweed). This challenge persists to this day, after 60 years of effort to break the evil cycle or to stimulate production by the host plant at a time when it is dormant but viable, while the invader is stimulated to grow and perish in adverse conditions to it.

4. As an example of another - and promising - ploy to tackle such challenges has been developed in Africa in a mixed cropping (or intercropping) system known as push-pull, which has been developed at Rothamsted Research with collaborators from the International Centre of Insect Physiology and Ecology (icipe) in Kenya. " It optimizes yields and is already working effectively in over 30,000 smallholder farms," says Toby Bruce. The intercrop, planted with the main crop, releases signals that repel pests out of the main crop (push) but attract the natural enemies of the pests into the crop. A trap crop is planted around the outside, which attracts the pests (pull). This method has collateral benefits as the companion plants (the intercrop) produce animal fodder and improve soil quality.

5. In appraising these systems we must rate their significance to applications in places such as Africa, where communications and transport are limited; moreover, questionable advertising ploys have muddled fundamental matters, although they may have extracted well-meaning donors, too gullible to perceive that the persuasions of a Send a Cow scheme may disguise, in small print, an appeal for pumps, latrines, and safe supplies of water. When the work on Striga was beginning about half-a-century ago Oxfam was being founded and started to campaign, now resorting to some modern technology in the forms of generators of solar power and wireless communications transmitting to farmers weather forecasts and market reports, together with mobile phones, motor-bikes and quad-bikes. The head of a group of nutritionists working in the Gambia moves around his patch by micro-light aircraft.

6. Universities and research on plant breeding institutes are springing up all over Africa, much of this "progress" being stimulated by Chinese investment and migrations of people to townships and slums and westernized diets and follies, with consequent emergence of premature degenerative diseases and continuing threats of pestilences such as HIV, malaria, TB, and a range of tick-borne diseases. Tourism and poaching, as well as civil strife and deforestation, add to the problems required in any measurement as responsible NGOs and charities, eyeing the weather and immediacy of the British harvest while

appraising the longer term challenges of global warming, must include biofuels and solar power in their thoughts for farming. A trustee of VEGA shared a taxi with a farmer from Zambia en route for a big agricultural show near Cambridge Cereals, at which new developments in breads were expected to yield results significant in our long-running Real Bread Campaign, which has extended its interests far beyond the debate over the national loaf - it's become far livelier and competitive.

7. The Zambian farmer has no plans to continue growing tobacco, but may consider growing cash crops such as tea and coffee or cotton (which may be GM), but she has begun successful crops of soya (which may also be GM). The work further north in Kenya on Striga-free cereals is an example where GM might be an acceptable application, altho the work on the push-pull system has introduced another nitrogen-fixing crop, suitable for the African rhizosphere; it's called desmodium. Fair Trade offers attractive value adding, especially if airfields, roads, and railways could be built to export sunshine, vitamins, and micro-nutrients from African horticulture to needy denizens of the high latitudes of northern Europe African farmers hardly claim a need for purchases of anything but seeds to fulful their 5-a-day requirements.

8. The Zambian farmer, long a resident of the country, was fair-skinned, and wore a hat at the cereals event against the sun. Our Trustee wore a hat too, in apt anticipation of rain, which fell as forecast. The debate over melanoma and vitamin D continues.

 
 
 

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