Agriculture Reference
In-Depth Information
future (Vance
et al.
, 2003).
For these reasons there is research on techniques of utilizing AM for
producing satisfactory yields of allium vegetables on soils lower in readily
available P than the current norm. In addition to the potential for improved P
uptake, root colonization by AM fungi can suppress root diseases (Whipps,
2004), possibly even allium white rot (Torres-Barragan
et al.
, 1996), and may
increase resistance to soil salinity and water stress as well as improving
micronutrient uptake (Stribley, 1990; de Melo, 2003). The hyphal networks of
AM fungi help to stabilize soil structure, particularly under soil management
systems where they are not disrupted, i.e. in low- or zero-tillage systems (Ryan
and Graham, 2002).
These additional potential benefits give further impetus for research to
develop systems of utilizing AM associations by allium crops. Among the
interesting developments is the co-inoculation of onion transplants with AM
fungi and phosphate-solubilizing bacteria. Seedlings so treated were able to
extract a greater fraction of their P uptake from the non-exchangeable fraction
of soil P or from sparingly soluble rock phosphate, a form of P fertilizer
permitted to organic farmers (Toro
et al.
, 1997). Crop rotations and break crops
which maintain high populations of native AM in soil and are of potential
benefit to leek crops have been designed (Sorensen
et al.
, 2005). There are
several reports of increases in both growth rate and yield of Japanese bunching
onions,
A. fistulosum
, following inoculation with AM (de Melo, 2003).
The effects of growing media - including different types of peat and
rockwool, species of AM inoculum and P concentration in liquid feed on
growth and root AM colonization percentage - have been studied for
transplant seedlings of
A. fistulosum
raised in modular cells (Matsubara
et al.
,
2002). The best results were from sowing seeds in 13 ml cells with 0.5 g
inoculum of
Gigaspora margarita
in a growth medium of brown peat and
vermiculite (9:1, v/v) fertigated initially with 1 ml per cell of a complete
nutrient solution containing just 5 ppm KH
2
PO
4
. By growing three or four
seedlings per cell, a robust root ball ideal for transplanting resulted after 4
weeks at 20°C following 1 week at 25°C in the dark for germination.
