| dc.description.abstract | The leaf and fruit spot disease of Citrus also
referred to as the Kitale syndrome, is a new disease to
Kenya. The causal agent is identified as Phaeoramu7aria
ango7ensis. The disease has assumed epidemic levels in
Western Kenya and it is a matter of time for it to
spread to all Citrus producing areas in the country.
The control of the disease has been difficult and
farmers have expressed fear that the fungus may be
resistant to fungicides. The isolation of the fungus
was reported to be difficult, and in culture the fungus
was said to sporulate only in media containing an
extract of Citrus leaf and fruit peel.
The objectives of this study were to "isolate and
characterise the causal agent of the leaf and fruit spot
disease, determine the most favourable conditions for growth
and sporulation of P. engoIenesis, and to carry
out in vitro tests on the resp5nse of the fungus to
selected fungicides.
Field surveys have shown that the disease is severe
on all species of Citrus growing in Trans-Nzoia
district. It was found that the disease occurred in
epidemics whose severity coincided with heavy rains from
August to December. Random sampling indicated that
60.8% of a 11 fall en 1eaves and 100% of the dropped
fruits were infected. On the average, leaf litter of a
single tree was found to contain about 39.4 x 108
spores.
Morphological characteristics of the fungus from
naturally and artificially infected plants, and axenic
cultures, showed that this fungus belongs to the genus
Phaeoramularia. However, from the literature, the
distinction between the genera Phaeoramu7aria and
Phaeoisariopsis is difficult and requires a taxonomic
reappraisal.
Isolates of P. ango7ensis were tested for
pathogenecity on disease free Citrus seedlings. An
inoculum from two week old solid cultures produced
typical disease s y m p tom son young Citrus plant s.
Lesions developed slowly, taking almost seven months for
definite necrotic lesions to be formed from the time of
inoculation.
Growth in liquid media was more than in solid
media with a mean difference of 17% ± 8 The Orange
leaf extract gave more growth than other media ( viz,
Tap water, Potato dextrose cornmeal, Potato carrot),
mean difference 25% ±. 15 Sparse sporulation was
observed on all solid media amended with dextrose. No
sporulation was observed in media without dextrose,
liquid media and in solid cultures more than two weeks 01
Growth occurred between 6-30oC with the optimum at
The fungus grew over a range of pH 3 to 8
with maximum growth occurring at initial pH of 5 to 6.
The best mycelial growth was obtained in cultures
incubated in continuous white light.
In vitro tests with Copper Oxychloride (50%WP),
Kocide 101 ( Copper Hydroxide, 50%WP) , Antracol
(Propineb 70%WP) and Dithane M45 (Mancozeb 80%WP) showed
that these fungic ides were effective in stopping spore
germination. However, Kocide 101 and Copper Oxychloride
were not effective against mycelial growth, but Antracol
and Dithane M45 were. Their differential effects on
mycelial growth was significant P<0.05, a 1though the
difference between Kocide 101 and Copper Oxychloride,
and between Di thane M45 and Antracol were not
significant. The LD50 for Antracol and Dithane M45 was
found to be less than 10ppm and that for Copper
Oxychloride and Kocide 101 more than 3000 ppm. | en |
