| dc.description.abstract | This study was undertaken to investigate the
type of variation in Colletotr·i·chumcoffean:um,
Noack the. causal agent of coffee berry disease in
Kenya. Samples of infected berries were collected
from different parts of Kenya where coffee is
widely grown.
It was found that C.coffeah:um has a wide
range of variation with respect to spore sizes,
spore shapes, sporulation capacity, growth and
pathogenicity. In terms of colour, some grey
isolates mutated to produce light coloured mutants.
These mutants retained their light colours.
Spore shapes ranged from cylindrical to
oval shapes. Every isolate produced a mixture of
spores of various shapes. However, over 95% of the
spores were cylindrical.
Spores did not have a significant difference
in diameter measurements. The average width was
4.lp. Spore lengths however varied from isolate to isolate.
There was also some variation within each of the
isolate as shown by the coefficient of variation
(3-33%). Mutants had spores similar to grey
isolates in terms of shapes and sizes.
When grey isolates from each district were
considered, it was found that all the districts
- xi -
except one could be grouped together in terms
of .their sporulation capacity.· The mutants,
however had a higher sporulation capacity than most
of the grey isolates.
Colour mutants tended to grow faster than the
grey isolate. Grey isolates from Trans Nzoia
district had a slower growth than those from Nandi
district.
Pathogenicity varied from isolate to isolate.
From each district grey isolates and mutants that
were weakly pat~!ogenic and others which were highly
pathogenic were obtained. \,Pathogenicity was shown
by reactions of six week old seedlings as well as
berries that were artificially inoculated. Some of
the isolates interacted significantly with coffee
varieties while others interacted negatively.
Four out of twenty isolates interacted positively
with HibrLdo de Timor. Two others interacted
positively with Rume Sudan. Two others interacted
negatively with SL 28.
When the reactions of coffee seedling
infection was classified as resistant (R), medium
resistant (MR), medium susceptible (MS) and
susceptibe (8) the isolates fell into different
groups. However, 32 isolates out of 52 isolates
fell into four main groups.
Isolates from different districts responded
( -:'xii r-
'to fungicides in a similar way. Most isolates
could not germinate in fungicides when concentrations
were above 25 ppm except in copper oxide.
Dithane M-45 which had not been used in controlling
coffee berry disease proved to be as effective as
the others in inhibiting germination of spores. | en |
