Dickeya
and
Pectobacterium
species cause blackleg / soft rot disease complex on potato
in Zimbabwe. The disease is seedborne and difficult to control. This research focused on
ways of increasing the inherent resistance of potato plants and tubers to blackleg and soft
rot. Two field experiments were conducted at the University of Zimbabwe campus plots
in 2008/9 and 2009/10 seasons in order to determine reproducibility of the results.
Sprouted tubers of cv. BP1 were inoculated with a mixture of
Pectobacterium atrosepticum
,
Pectobacterium carotovorum subsp.
brasiliense and
Dickeya dadantii
.
The inoculated tubers were planted in plots treated with different fertilizer combinations.
The treatments were: 1) compound S (7N: 21P: 8K) + ammonium nitrate (34 %N); 2)
compound D (7N: 14P: 7K) + calcium nitrate (19 Ca: 15.5N); 3) compound S + calcium
nitrate and 4) compound D + ammonium nitrate. Blackleg disease incidence and severity
were recorded fortnightly starting from 2 weeks after crop emergence (WACE) while
soft rot disease was assessed at physiological maturity. Blackleg incidences and severity
were significantly lower (P < 0.05) in the plots where calcium nitrate was applied for
both experiments. Blackleg disease incidence was reduced by more than 20% in both
experiments 1 and 2. Soft rot incidence in the progeny tubers was also significantly
reduced by the calcium treatment. In addition, calcium amendment significantly reduced
(P < 0.05) soft rot losses of tubers in storage. Calcium nitrate was effective in reducing
blackleg and soft rot diseases in combination with either compound D or compound S.
The yield was significantly higher in plots where compound S was applied as a basal
fertilizer than that recorded in plots treated with compound D fertilizer. This study shows
that calcium soil amendments reduce blackleg and soft rot diseases under Zimbabwe’s
growing seasons in red fersiallitic soils. Compound S produces better results in potato
production than compound D and farmers should be encouraged to use compound S
when growing potatoes.
