permaculture

["Lawrence F. London, Jr." <lflj@intrex.net>]

Agron. Sustain. Dev. 28 (2008) 33-46
DOI: 10.1051/agro:2007051

Role of nutrients in controlling plant diseases in sustainable agriculture. A 
review
Christos Dordas

Aristotle University of Thessaloniki, Faculty of Agriculture, Laboratory of
Agronomy, University Campus, 54124 Thessaloniki, Greece

(Accepted 16 October 2007; published online 9 January 2008)

Abstract - In recent years the importance of sustainable agriculture has risen to become one of the most important 
issues in agriculture. In addition, plant diseases continue to play a major limiting role in agricultural production. 
The control of plant diseases using classical  pesticides raises serious concerns about food safety, environmental 
quality and pesticide resistance, which have dictated the need for alternative pest management techniques. In 
particular, nutrients could affect the disease tolerance or resistance of plants to pathogens. However, there are 
contradictory reports about the effect of nutrients on plant diseases and many factors that influence this response are 
not well understood. This review article summarizes the most recent information regarding the effect of nutrients, such 
as N, K, P, Mn, Zn, B, Cl and Si, on disease resistance and tolerance and their use in sustainable agriculture. There is 
a difference in the response of obligate parasites to N supply, as when there is a high N level there is an increase in 
severity of the infection. In contrast, in facultative parasites at high N supply there is a decrease in the severity of 
the infection. K decreases the susceptibility of host plants up to the optimal level for growth and beyond this point 
there is no further increase in resistance. In contrast to K, the role of P in resistance is variable and seemingly 
inconsistent. Among the micronutrients, Mn can control a number of diseases as Mn has an important role in lignin 
biosynthesis, phenol biosynthesis, photosynthesis and several other functions. Zn was found to have a number of 
different effects as in some cases it decreased, in others increased, and in others had no effect on plant 
susceptibility to disease. B was found to reduce the severity of many diseases because of the function that B has on 
cell wall structure, plant membranes and plant metabolism. Cl application can enhance host plants'
resistance to disease. Si has been shown to control a number of diseases and it is believed that Si creates a physical 
barrier which can restrict fungal hyphae penetration, or it may induce accumulation of antifungal compounds. Integrative 
plant nutrition is an essential component in sustainable agriculture, because in most cases it is more cost-effective 
and also environmentally friendly to control plant disease with the adequate amount of nutrients and with no pesticides. 
Nutrients can reduce disease to an acceptable level, or at least to a level at which further control by other cultural 
practices or conventional organic biocides are more successful and less expensive.

****************************************************************************************************
Agronomy for Sustainable Development

Vol. 28 No. 1 (January-March 2008)
Agronomy for Sustainable Devolopment


    * Pharmaceutical crops in California, benefits and risks. A review     p. 
1
      Michelle Marvier
      Abstract | PDF file (4.824 MB) | References


    * Bacillus thuringiensis: applications in agriculture and insect 
resistance management. A review     p. 11
      Vincent Sanchis and Denis Bourguet
      Abstract | PDF file (969.4 KB) | References


    * Genetically modified glyphosate-tolerant soybean in the USA: adoption factors, impacts and prospects. A review 
  p. 21
      Sylvie Bonny
      Abstract | PDF file (294.8 KB) | References


    * Role of nutrients in controlling plant diseases in sustainable 
agriculture. A review     p. 33
      Christos Dordas
      Abstract | PDF file (1.615 MB) | References



    * Grasslands for bioenergy production. A review     p. 47
      Enrico Ceotto
      Abstract | PDF file (2.277 MB) | References


    * Soils and sustainable agriculture. A review     p. 57
      R. Lal
      Abstract | PDF file (444.7 KB) | References


    * Soil-erosion and runoff prevention by plant covers. A review     p. 65
      Víctor Hugo Durán Zuazo and Carmen Rocío Rodríguez Pleguezuelo
      Abstract | PDF file (1.192 MB) | References



    * Denitrification in cropping systems at sub-zero soil temperatures. A 
review     p. 87
      Rebecca L. Phillips
      Abstract | PDF file (683.4 KB) | References


    * Saffron, an alternative crop for sustainable agricultural systems. A 
review     p. 95
      F. Gresta, G.M. Lombardo, L. Siracusa and G. Ruberto
      Abstract | PDF file (1.272 MB) | References


    * Sustainable pest management for cotton production. A review     p. 113
      Jean-Philippe Deguine, Pierre Ferron and Derek Russell
      Abstract | PDF file (408.5 KB) | References


    * Agri-environmental indicators to assess cropping and farming systems. A 
review     p. 139
      Christian Bockstaller, Laurence Guichard, David Makowski, Anne Aveline, 
Philippe Girardin and Sylvain Plantureux
      Abstract | PDF file (343.1 KB) | References


    * Methodological progress in on-farm regional agronomic diagnosis. A 
review     p. 151
      Thierry Doré, Cathy Clermont-Dauphin, Yves Crozat, Christophe David, Marie-Hélène Jeuffroy, Chantal Loyce, David 
Makowski, Eric Malézieux, Jean-Marc Meynard and Muriel Valantin-Morison
      Abstract | PDF file (201.9 KB) | References


    * Ex ante assessment of the sustainability of alternative cropping systems: implications for using multi-criteria 
decision-aid methods. A review     p. 163
      Walid Sadok, Frédérique Angevin, Jacques-Éric Bergez, Christian Bockstaller, Bruno Colomb, Laurence Guichard, 
Raymond Reau and Thierry Doré
      Abstract | PDF file (235.9 KB) | References


===============================
Miscellaneous F O L L O W U P S
===============================

Douglas Woodward said:
"It is known that fertilization with high levels of nitrogen produces
plant sap containing more free amino acids which sucking insects can
more readily use, while moderate levels of nitrogen favour complete
proteins, presumably more usually non-mobile rather than dissolved
in the sap, and in any case requiring more effort at digestion."

Francis Chaboussou
"Healthy Crops: A New Agricultural Revolution"
1982  http://gaiafoundation.org
Excerpts:

    Almost all conventional chemical agricultural technologies create
   favourable conditions for the growth of pest and disease organisms:
   this book shows how much of the problem can be explained through
   increases in soluble nitrogen, amino-acid and sugar concentrations
   in the plant cells. For example, heavy applications of soluble
   nitrogen fertilisers increase the cellular amounts of nitrate,
   ammonia and amino acids faster than can be used for the synthesis of
   protein. Similarly herbicides, even in recommended concentrations,
   inevitably affect the crop plant somewhat (perhaps not visibly), the
   main effect being a temporary reduction in protein synthesis-- the
   most sensitive of metabolic processes. Spraying with almost any
   pesticide or fungicide has the same effect. These reductions in the
   rate of protein synthesis result in temporary accumulation of amino
   acids. Therefore, while the immediate attack by a pest may be
   reduced by a pesticide, the susceptibility of the crop is increased:
   when offered soluble free nutrients, pests grow better and multiply
   faster. In this sense therefore, agro-chemicals and poisons cause
   pests and diseases.
   This conclusion suggests that pest and disease organisms cannot use
   protein and polysaccharides directly and require soluble amino acids
   and sugars for growth. Lutzenberger often argued that various
   insects and even fungal pests lack proteolytic enzymes (as implied
   in his introduction about leaf-cutter ants), but some insects, fungi
   and other organisms do in fact have them. The situation is therefore
   complex. Chaboussou's empirical evidence clearly demonstrates that
   pests and disease organisms grow and multiply faster when the plant
   contains more soluble free nutrients. In other words, the
   biochemical and physiological state of the plant is strongly
   affected by the method of cultivation, and this controls whether
   pests can invade: one can therefore avoid pests and diseases by
   methods of cultivation that limit the amounts of soluble nutrients
   in the plant.

   A healthy plant, a plant in metabolic balance, is either in repose,
   for example in hibernation or, in dry climates, in estivation, or it
   is growing as vigorously as it can, depending on the supply of
   nutrients, water and weather. When a plant is in repose the sap is
   poor in amino-acids; they were used up when preparing for the period
   of quiet. When it is growing vigorously the sap is also poor in
   amino-acids. Intensive protein synthesis uses up the amino-acids
   produced in the cell as fast as they appear. In both cases the plant
   is not nutritious for its parasites. They may just be able to
   survive, but they cannot thrive. They need a very high level
   ofsoluble food to build their own proteins: not only amino-acids,
   but also sugars, the sources of energy for the synthesis of
   proteins, and mineral nutrients to help build their more complicated
   proteins, such as the enzymes. Other important ingredients are the
   nucleotides, the pieces of the genetic code. Plants that are not
   nutritious for the pests are also not palatable to them, the
   parasites ignore them. As to which particular pest or parasite will
   thrive, this depends on the proportion of the different ingredients


   We have shown in experiments that, as compared to grapevines treated
   solely with pure water, treatments using various dithiocarbonates
   (zineb, maneb, propineb) brought about a significant increase in
   attacks of Oidium. Vanev and Celebiev (1974) have also shown
   stimulation of the development of Oidium (/Uncinula necator/) and
   grey mould (/Botrytis cinerea/) on grapevines by zineb-based
   chemicals (Fig. 1).
   It seems logical that these 'biological imbalances' brought about by
   chemical pesticides, whether in the animal or plant kingdoms, should
   have the same cause. Thus captan, though harmless to natural
   predators, produces not only a proliferation of mites, but also of
   /Oidium/ on the apple tree. In addition, it promotes development of
   the bacterial disease crown gall on the cherry tree (Deep and Young,
   1965). These authors state that their findings do not coincide with
   the theory of antagonism [i.e. suppression of beneficials leading to
   a bloom of parasites].