Agriculture Reference
In-Depth Information
the holes may lead to glazing of their inner surfaces with adverse effects on
root penetration (Auxt
et al.
,
).
Mycorrhizal infection and initial root growth
Apple root systems in the orchard are commonly infected with vesicular-
arbuscular mycorrhizal (VAM) fungi (Atkinson,
), and pear roots readily
become mycorrhizal (Gardiner and Christensen,
). The VAM fungi form
branched haustorial structures within the root cortexcells and have mycelium
or hyphal strands which extend well into the surrounding soil. Water and
nutrients absorbed by this mycelium pass back into the root so that the effec-
tive absorbing surface of the latter is greatly increased. This fungal infection
has beneficial effects on phosphorus nutrition, trace element and water up-
take, hormone production, nitrogen fixation and resistance to root disease,
although it results in a drain on carbohydrate resources (Gianinazzi-Pearson
and Gianinazzi,
).
Infection is likely to occur naturally in the course of traditional nursery
and orchard practice. The increasing use of micropropagation, the rooting of
cuttings in sterilized media and soil fumigation in the nursery and orchard,
reduce the likelihood of this. Delays in mycorrhizal infection may have serious
adverse effects. Mosse (
; Marschner,
), using apple seedlings, found mycorrhizal plants
to have
% more shoot dry weight than
non-mycorrhizal ones and to have higher concentrations of K, Ca and Fe
and lower concentrations of Mn. Sewell
et al.
(
% more root dry weight and
) also found apple leaf Mn
concentrations to be reduced in the presence of a mycorrhizal fungus and
found leaf P levels to be increased in the presence of VA mycorrhiza and grass.
Sewell and Roberts (
) showed that in sterilized soil containing only
mg P g
−
apple seedlings inoculated with
Glomus caledonicum
grew more than
eight times as rapidly as did non-mycorrhizal seedlings. In high-phosphorus
soils responses to mycorrhizal infection are less dramatic, but still large (Sewell
and Roberts,
; Morin
et al.
,
).
clonal pear rootstock with
Glomus
sp. This resulted in a three-fold increase
in shoot growth and a smaller and non-significant increase in root growth
by
Rapparini
et al.
(
) inoculated micropropagated plants of OH
×
F
months after inoculation, and also a greater development in the second
growing season after overwintering.
Orchard tree root systems
The mature tree root system includes roots which differ in age, thickening and
suberization.
