Agriculture Reference
In-Depth Information
supply is quickly approaching complete depletion, [108]. Production of
phosphorus on the island nation has gone from 2.3 million tons (valued at
$68/ton) in 1973 to a mere 250,000 tons (valued at only $44/ton) in 2001
[1]. The aggressive mining had adverse effects on vegetation and soil, de-
struction of the local ecology and economy, and depletion of the mineral
content of the land itself [1,108].
According to the worldwide phosphorus production data, consump-
tion and population growth are directly correlated [109]. Consumption
and depletion of phosphate rocks are projected to rise with continued in-
creases in population and food demand [109]. Breeding for varieties with
higher phosphorus use effi ciency could help to improve the worldwide
management of this valuable resource, while providing enough food for
the future. Factors to be considered in such breeding programs include
improvement of root architecture, organic acid production and exudation,
establishment of stronger mycorrhizal associations, more effi cient phos-
phate uptake systems, and better phosphate physiology, which include
less allocation of phosphate towards phytate biosynthesis and accumula-
tion. Much of the research to improve phosphorus uptake effi ciency has
focused on improved morphology or physiology of the root system. In
many soils the total amount of phosphorus can be high, however for the
most part is present in organic forms that are unavailable to crops. One of
the mechanisms used by crops produced in low-P systems is to alter root
structure, allocating more carbon to the roots, increasing the root-to-shoot
ratio [110,111].
Arabidopsis
produced under phosphate defi ciency shows
modifi cations to the root architecture, redistributing energy from primary
to lateral root growth [111], not to mention higher anthocyanin accumula-
tion. Under P-defi cient conditions, genotypes effi cient in the acquisition
of phosphorus have increased lateral root length allowing for greater ex-
ploration and foraging of the topsoil [112,113]. Change in root distribu-
tion has also been shown in tobacco, rape, spinach, and tomato [113-115].
Lynch and Brown [112] illustrated that genotypes with superior growth in
low-P environments have root traits advantageous to topsoil foraging. It
was also concluded that these inheritable traits are mediated by ethylene
production and QTLs were identifi ed through genetic mapping and used
specifi cally for breeding towards improved phosphorus acquisition in low-
input systems.
