Agriculture Reference
In-Depth Information
observations of nursery tree growth by Thompson (
). He found that when
nursery trees of apples, quince, cherries and some plums were planted in rows
cutting at right-angles across the sites of previous rows of these species the
growth of apples, and to a lesser extent of quince, was severely depressed
when they were growing on land previously occupied by apples. The growth
of cherry rootstocks was not depressed when growing on old apple land but
was less good where they followed stone fruits. Apple tree growth shows large
responses to soil fumigation of old apple land whereas cherry tree growth on
the same land does not (Pitcher
et al.
,
; Jackson,
). From such obser-
vations and experiments Savory (
) concluded that cherry and apple
were subject to separate specific replant diseases and the fungus
Thielaviopsis
basicola
(Berk. & Br.) Ferraris, which does not affect apple tree growth, was
subsequently identified as the cause of cherry specific replant disease (Sewell
and Wilson,
,
). Further work on apple replant disease, however, led Sewell
(
) to conclude that this is not strictly specific. The growth of apple is con-
siderably diminished when planted after a number of other crops and the
growth of some other crops may be diminished when these are planted after
apple. Soil sterilization by heating increased
Malus
seedling growth more on
ex-
Robinia
than on ex-
Malus
soil and
Robinia
and
Tilia
growth in ex-
Malus
soil
was greatly increased when this was fumigated (Sewell and Roberts,
).
A replant disease condition can be induced by growing apple trees in the
soil for only one year (Oostenbrink and Hoestra,
) and can persist for at
least five years after grubbing (Thompson,
). Responses to fumigation are
a function of soil pH, being much greater on alkaline and neutral soils than on
acidsoils.Croppingresponsescanbeverylarge,e.g.
).
Under some conditions where soil phosphorus levels are low, both pre-planting
pot tests and field responses to fumigation may be low or even negative. This
is because of the effect of fumigation in killing mycorrhizal fungi. In such
circumstances both fumigation and P fertilizer treatment may be needed: the
need for fumigation being shown only by pot tests carried out with P-fertilized
soil (Sewell
et al.
,
-
%(Hoestra,
).
Theetiologyofapplereplantdiseaseinvolvesthebuild-upofpathogenicorgan-
isms in the soil of apple orchards and the persistence of these for an extended
time after grubbing, either because they form resting stages or they possess a
strong saprophytic ability.
Actinomycetes
Circumstantial evidence, including the effect of soil pH and responses to dif-
ferent fumigants, suggests that
actinomycetes
are involved (Hoestra,
). Otto
and Winkler (cited by Utkhede and Smith,
b) found that the severity of
