Monsanto develops Aluminum Resistant biotech seeds

From a testing company

From a testing company website:

Very little Al+++ in the soil solution is required to cause damage to most plants. Few, if any plants grown for commercial purposes in this country will tolerate more than 1.0 ppm of soluble Al+++, and most will have some problems at levels greater than 0.5 ppm.  

Aluminum is a common metal in soils.  It is a significant toxin in acid soils (or soils exposed to acid rain) causing stunted roots (no rootlets ergo poor plant health).  Good picture on that site as well.

Here are that site's general conclusions

-- When the soil pH is below 5.0, soluble Al is almost certainly a problem.

-- When the soil pH is between 5.0 and 5.5, soluble Al likely a small problem

-- When the soil pH is between 5.5 and 6.0, soluble Al is not likely to be a significant problem

-- When the soil pH is above 6.0, soluble Al is almost certainly not a problem.

-- Lime is the solution to excess soluble Al in the topsoil

-- Gypsum may be needed to correct excess soluble Al in the subsoil

Hope that's helpful - I learned something so... thanks!   The genetic modification to withstand Aluminum is probably done to keep an acid tolerant plant from surviving the low pH but stunting from Al+++ poisoning.