| dc.description.abstract | A survey was conducted in the coffee growing
areas of Kenya during the months of August, September,
and October 1987 to determine the ecological distribution
of bacterial blight of coffee and its incitant
Pseudomonas syringae, Van Hall.
The survey covered the three main coffee growing
zones viz. upper middle zone 1 (UM1), upper middle
zone 2 (UM2), which forms the main coffee growing
zone and upper middle zone 3 (UM3) which is the marginal
coffee zone.
Three types of.Pseudomonads appeared consistently
and relatively often and were categorized according
to colony characteristics on nutrient Sucrose agar and
'biochemical:;physiological characteristic ics. The three
groups were designated as Pseudomonas SPP 1, 2 and 3.
Pseudomonas spp 3 was found to be non fluorescent and
non pathogenic to coffee.
Pseudomonas SPP-l was also found to be non pathogenic
and was.characteristic of a saprophyte because
of its fast growth and positive Arginine dehydrolase
action. Further test showed that the species was
Pseudomonas fluorescens, bio-type 1.
Pseudomonas SPP 2 was found to be Arginine dehydrogenase
negative, was not a gelatin liquifier and
was oxidase negative. These reactions suggested that
Pseudomonas spp~was Pseudomonas syringae, Van Hall.
This was in agreement with characteristics of Pseudomonas
syringae, Van Hall reported earlier (Ramos and
Shavdia 1976, Ramos, 1979). Pathogenic tests on
various isolates of Pseudomonas SPP-2 showed that the
isolates were all pathogenic to coffee.
Eight isolates of Pseudomonas Spp~(Pseudomonas
syringae, Van Hall) were isolated from eight widely
separated geographical areas which were all found to
fall in the marginal coffee areas (Upper middle zone-
3). No isolate with characteristics similar to Pseudomonas
syringae was isolated from UM-l and UM-2. The
spread of bacterial blight was found to be confined
in certain areas of UM-3. The pathogen was isolated
only in these areas.
The growth patterns of Pseudomonas syringae, Van
Hall in its natural host coffee (Coffea arabica L.)
followed a typical bacterial growth curve. After inoculation
by injection-infiltration method, the population
of the bacteria initially increased rapidly, having
a logarithmic phase running from the 1st day of inoculation
to the 3rd day, transition 3rd - 5th day and
and finally the stationary phase where the bacteria
population remained stable or declined slowly. Initial
level of inoculum was found to influence the rate of
growth and final population level achieved in the
tissues.
Kinetics of Pseudomonas syringae multiplication
in the foliage of three varieties (SL-34, SL-28 and
Catimor) showed that the rates of multiplication;
final population, degree of colonization and severity
of symptoms was highest in SL-28, lowest in Catimor
and intermediate in SL-34. The reactions suggest
that Catimor has the highest, SL-34 intermediate
I
and SL-28 the lowest resistance to bacterial blight
of coffee.
Pseudomonas syringae was found to multiply
equally well in young and old leaves of coffee but
at a lower rate in old leaves. However, the
pathogen was found to multiply at faster rates and
to higher final population in young leaves compared
to old leaves. Symptoms assessment showed that old
leaves were more resistant than young leaves. This
observation i~ the greenhouse was found to be in agreement
to the observations made in the field. Age resistance
was found to be correlated to the apparent inability
of the pathogen to multiply extensively in the
old leaves. However, the pathogen was found to multiply
at similar rates and final populations in both the
young and old leaf extracts. This work suggested that
the differences in multiplication between the young
and old leaves was not due to unfavorable nutrient
status in the old leaves· | en |
