Agriculture Reference
In-Depth Information
apple replant disease in Germany was correlated with
actinomycete
presence.
Apple seedlings, and rowan (
Sorbus aucuparia
) and pear (
Pyrus communis
) root-
stocks were strongly infected with
actinomycetes
when planted in soil from an
apple orchard but rootstocks of cherry, plum and rose were not (Otto
et al.
,
). The
actinomycetes
penetrate the epidermal cells and damage the cortex
in such a way that the cortexand rootlets die off. They enshroud root hairs
and cause their collapse (Otto and Winkler,
; Szabo
et al.
,
).
Pythium
Several studies have shown an association between
Pythium sylvaticum
and re-
plant disease (Utkhede and Smith,
) found that all tested
isolates of
P. sylvaticum
and some isolates of other
Pythium
species significantly
reduced the growth of apple seedlings and that the isolates of most virulence
to apple were of low virulence to cherry. He noted that the disease profile of
apple replant disease is compatible with a causal role for
Pythium.
a). Sewell (
Other fungi
Penicillium janthinellum
,
Constantinella terrestris
,
Peniophore sacrata
,
Penicillium clavi-
forme
and
Cylindrocarpon
spp. have all been reported to be associated with apple
replant disease.
Bacteria
Bacillus subtilis
and
Pseudomonas putida
have been found to stunt the growth of
young apple trees.
⁄
Given the range of potential causal agents, resistance might seem unlikely.
However, when sensitivity is assessed by response to soil fumigation, 'M.
' and
'MM.
' appeared to be particularly sensitive and more vigorous rootstocks
especially 'M.
', 'M.
' and 'Crab C' less so. The effect is not solely associated
with vigour; 'M.
' and 'M.
' appeared to be relatively tolerant ( Jackson,
) and 'M.
' to have a high degree of field tolerance (Oehl and Jackson,
' (the
AR series) also show appreciable field tolerance. This may imply a single domi-
nant cause of ARD in the East Malling soils and it is notable that 'Northern
Spy', which also showed some apparent tolerance there, gave much smaller
responses to soil fumigation on an old apple orchard site in New Zealand than
did 'MM.
). Some rootstock clones produced by crossing 'M.
' with 'MM.
', 'MM.
' and 'M.
' (Ryan,
).
Even though other plants appear able to induce apple replant disease in the
soil, the main problem is that of replanting on old apple orchard sites. This
is because in most countries the best land for apple production has already
grown that crop and because the disease is extremely persistent.
