Target plants, stress

Biofuels rely on organic feedstocks such as plant oil, food wastes and trees but their larger scale and rapid exploitation to meet government targets is stressing large areas of land and associated systems such as water, food production and recreation. A truly sustainable future for biofuels and other eco-system exploitation for industrial value requires a better understanding and more quantitative assessment of a number of critical issues ... 

The role of environmental factors in allelopathic inhibition. Moisture and nutrient stress, high temperature, light intensity, plant density, and the presence of pathogens can all alter the response of target plants to allelochemicals and also the production or release rates of allelochemi-cals by source plants. Chemicals that are not toxic at certain concentrations in a laboratory assay may, in fact, be significantly inhibitory under stressful field conditions. 

Water stress reduces the rate of photosynthesis in plants. In soybean crops, water stress leads to a loss of root integrity. The failure of the lower leaves to intercept light in a mature crop is compounded by the water-related limitations. The result is that lower leaves abscise and, because seed pods (yield) are supplied with assimilate mainly from leaves at the same nodal position on the stem, they in turn are lost and overall yield is reduced. The control of water stress in crops is a major PGR target in yield maintenance. The alleviation of water stress in developing crops, particularly in arid areas, is also desirable. 

A holistic view regarding the mode of action of phenolic allelochemicals recognizes the effects of these compounds as one of several stresses on plants. Complexes of the individual phenolic compounds become the effective unit causing allelopathy. In summary, explanations of the mode of action of phenolic allelochemicals must take into account that these compounds act in concert, the different compounds vary in toxicity but they have similarities in their mechanisms of action, and they all appear to disrupt cellular functions at multiple target sites. 

Organic systems seek to have a more measured pace of crop growth which encourages a more robust plant to resist pests and diseases. The greater balance of biodiversity achieves a more natural level of pest predators and a non-stressed crop is more likely to resist disease. Unless specifically targeted, some pesticides will kill beneficial as well as pest insects. 

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