Sources of CBD inoculum. Of the Col

Sources of CBD inoculum. Of the Colletotrichum species, which usually colonize the
maturing bark of branches of C. arabica in Kenya (GIBBS, 1969 ; HINDORF, 1970 ; VERMEULEN,
1970) only Colletotrichum coffeanum NOACK (sensu HINDORF) is pathogenic
to green berries of CBD susceptible trees. GIBBS (1969) found that the sporulating
capacity (conidia/cmZbark per hour) of the CBD pathogen is usually not more than
2 7 ~ (an average of 10 conidia/cm 2 per h) of the sporulating capacity of the whole
Colletotrichum population of the bark. In contrast, green infected berries with active
lesions produce only spores of C. coffeanum and the sporulating capacity can be as
high as 7-19 × 10 a conidia/cm 2 per h. Lesions on infected ripe berries may have similarly
high sporulating capacities, but apart from C. coffeanum other Colletotrichum
spp. are usually present as well.
Green infected berries with active lesions are, therefore, the best source ofinoculum
for initial isolation for two reasons: (1) low contamination with other non-pathogenic
Colletotrichum spp. and (2) optimum pathogenicity of the isolates (Coot

Results (Vietnamese) 1:

Sources of CBD inoculum. Of the Colletotrichum species, which usually colonize thematuring bark of branches of C. arabica in Kenya (GIBBS, 1969 ; HINDORF, 1970 ; VERMEULEN,1970) only Colletotrichum coffeanum NOACK (sensu HINDORF) is pathogenicto green berries of CBD susceptible trees. GIBBS (1969) found that the sporulatingcapacity (conidia/cmZbark per hour) of the CBD pathogen is usually not more than2 7 ~ (an average of 10 conidia/cm 2 per h) of the sporulating capacity of the wholeColletotrichum population of the bark. In contrast, green infected berries with activelesions produce only spores of C. coffeanum and the sporulating capacity can be ashigh as 7-19 × 10 a conidia/cm 2 per h. Lesions on infected ripe berries may have similarlyhigh sporulating capacities, but apart from C. coffeanum other Colletotrichumspp. are usually present as well.Green infected berries with active lesions are, therefore, the best source ofinoculumfor initial isolation for two reasons: (1) low contamination with other non-pathogenicColletotrichum spp. and (2) optimum pathogenicity of the isolates (Coot<, 1976).Initial isolation of the CBD pathogen is achieved by incubating green infected berriesfor 48 h at 20-24 °C on moist sterilized sand or cellulose wadding in closed but somewhatventilated plastic boxes, followed by plating the conidia on 3.4 ~ (Oxoid) maltextract agar containing 0.04~ streptomycin. Optimum spore production is usuallyobtained after 10 days incubation of the cultures at 22°-24 °C (Coot<, 1976). Inoculationtests were carried out with spore suspensions of 2 × 106 conidia/ml freshly preparedfrom these pure cultures and with proved spore viability in excess of 80 ~o.Isolates of the pathogen are always obtained from unsprayed coffee trees (preferablyof the cultivars SL28 or SL34). So far, variation in (vertical) pathogenicity betweendifferent isolates has not bee noticed, one possible explanation being that mostcoffee grown in Kenya is highly susceptible to CBD and selection pressure for morevirulent pathotypes is virtually absent. An intensive investigation into the existenceof different pathotypes for the CBD pathogen is now being undertaken at the CoffeeResearch Station. In the meantime, inoculum for preselection tests is always preparedfrom spore suspensions of at least two pathogenic isolates collected from distinctlydifferent locations.