Examination of the results of Series II inoculations
shows that in each variety tested, susceptibility to
Gangrene, as caused by either isolate, increases with
the length of the storage period. The varieties are
immune at lifting and during most of the dormant period.
However, with sprouting, susceptibility is increased.
Isolates 1 and 2 differed in their pathogenicity
depending on the tuber variety concerned. Thus, Doon
Star, Catriona and Kerr's Pink were more susceptible
to isolate 1, and Golden Wonder and Home Guard were
more susceptible to isolate 2.
As regards susceptibility to isolate l,the
varieties may be placed in the following order:-
a) Catriona and Home Guard, b) Doon Star, c) Golden
Wonder and Kerr's Pink. Similarly, with isolate 2
the varieties are placed in the order, a) Home Guard
b) Golden Wonder, c) Doon Star and Kerr's Pink and
d) Catriona.
No conclusive evidence was produced regarding the
pathogenicity of isolate 5 on any of the varieties
tested. It seemed that this isolate was not a virulent
parasite.
The results of Series III inoculations show that
storage at a higher temperature before inoculation
renders the tubers more susceptible to Gangrene.
However, storage at a low temperature subsequent to
inoculation increases susceptibility to Gangrene, the
rots formed being more extensive in the tubers kept
in the insulated store room than in those kept at
room temperature.
Series III inoculations also indicated that
different potato varieties can be graded according to
their susceptibility. The first set of inoculations
showed that the tubers tested could be placed in the
following order of increasing susceptibility with
regard to isolate 1: a) Kerr's Pink,b) Doon Star and
Arran Banner,c) Golden Wonder,d) Arran Pilot,e)
Catriona and Home Guard. Similarly, with regard to
isolate 2, the order of the varieties is a) Kerr's
Pink,b) Golden Wonder,c) Arran Banner and Doon Star,
d) Arran Pilot,e) Home Guard,f) Catriona.
In the second set of inoculations the order of
increased susceptibility to isolate 1 is a) Home Guard,
Doon Star and Kerr's Pink, b) Arran Pilot, c) Arran
Banner, d) Golden Wonder and e) Catriona. With
isolate 2 the sequence is a) Doon Star, Kerr's Pink
and Golden Wonder, b) Arran Pilot, c) Arran Banner,
d) Home Guard and e) Catriona.
It is also evident from the results that some
varieties, e.g. Kerr's Pink, Arran Banner and Catriona
were more susceptible to isolate 2 in both sets of
inoculations. In addition, Doon Star tended to be
more susceptible to this isolate in the later set of
inoculations.
Series IV inoculations showed conclusively, that
soil and storage conditions can be responsible for
the development of a Skin Necrosis type of rot on
infected tubers. The Skin Necrosis symptoms developed
on only 51.3% of those tubers which were grown on
peat soil and kept under low temperature storage
conditions. The remaining tubers all developed
deeper rots which , although shallow, were quite
distinct from those showing Skin Necrosis symptoms
