Wheat root colonizers

Z. Rengel, G. Ross, and P. Hinsch, Plant genotype and micronutrient status influence colonization of wheat roots by soil bacteria. J. Plain Niilr. 21 99 (1998). 

Two cases will be presented to illustrate the difficulty in establishing allelopathy and in linking the agent to poor crop growth. Specifically, the role of phenolic acids and the role of toxin-producing pseudomonads colonizing wheat roots will be examined. 

Specificity of Root Colonizers. Two isolates of Pythium representative of the early colonists of glyphosate treated seedlings for both beans and wheat from organic and mineral soil were examined and identified by Dr. 

Taken into account that Secale cereale, for instance, exudes DIBOA, which is converted to BOA, root colonizing bacteria may perform 2-aminophenol production, resulting in phenoxazinones, compounds that probably influence the species composition of micro-organisms within the rhizosphere. On the other hand, hydroxamic acid free species coexisting with rye or wheat can have an advantage when 2-aminophenol producing... 

VAN VUURDE J.W.L. and SCHIPPERS B.. 1980. Bacterial colonization of seminal wheat roots. Soil Biology and Biochemistry, 12, 559-565. 

Mycorrhiza have been shown to be very important for P uptake (Bolan 1991 van der Heijden et al. 2006). In wheat, the arbuscular mycorrhizal colonization decreased with increasing soil P. It was reduced from 60% of root length colonized at 10 mg P kg-1 soil to 10% at 27 mg P kg-1 soil (Covacevich et al. 2007). This was independent of shoot P contents. 

Elliott, L.F., Lynch, J.M. Plant growth-inhibitory pseudomonads colonizing winter wheat (Triticum aestivum L.) roots. Plant Soil 1985 84 57-65. 

Colonization of barley, wheat and maize and rice roots by Glomus intraradices resulted in strong induction of transcript levels of the pivotal enzymes of methylerythritol phosphate pathway of isoprenoid biosynthes i.e., 1 -deoxy-D-xylulose 5-phosphate synthase (DXS) and 1 -deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) (Walter et al., 2000). At the same time six cyclohexenone derivatives were characterized from mycorrhizal wheat and maize roots. DXS2 transcript levels are low in most tissues but are strongly stimulated in roots upon colonization by mycorrhizal fungi, correlated with accumulation of carotenoids and apocarotenoids (Walter et al., 2002). Some reports show that the AM symbiosis may cause an increase, decrease, or no change in the plant defense reactions (Guenoune et al., 2001 Mohr et al., 1998). 

Figure 5. Rate of colonization of entire root systems of 2-week old wheat seedlings by Pythium or Fusarium spp. Plants treated with 2 ig of glyphosate were compared with control plants (O —). The plants were grown at 25C, in either mineral or organic soils adjusted daily to field capacity (-0.06 Bar).

In pure-culture inoculation experiments, made by Rovira (1963), it was found that Azotobacter did not colonize the roots of lucerne, maize, tomato, or wheat to any great extent. Clostridium and a facultative nitrogen-fixing bacillus were moderate colonizers. In mixed-culture, or unsterilized soils, where competition is likely to be very intense, one would expect even less success in attempts to influence the rhizosphere population by adding foreign organisms. 

Monfort, E., Lopez Llorca, L. V., Jansson, H. B., Salinas, J., Park, J. O., Sivasithamparan, K. Colonization of seminal roots of wheat and barley by egg-parasitic nematophagous fungi and their effects on Gaeumannomyces graminis var. tritici and development of root-rot. Soil Biol Biochem 2005, 37,1229-1235. 

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