Virulence of colletotrichum kahawae strains and their effect on resistant arabica coffee varieties in Tanzania
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Date
2008
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Publisher
Sokoine University of Agriculture
Abstract
The virulence of 26 Colletotrichum kahawae strains collected from different coffee
growing areas in Tanzania was studied under laboratory conditions. Cultural and
morphological characters on malt extract agar indicated variations amongst strains.
Virulence tests both on detached coffee green berries and hypocotyls distinguished
between highly and less virulence strains. Initial symptom appearance showed
positive correlation to sporulation. Lesion size showed positive correlation to
sporulation capacity and percent berry infection; and sporulation capacity and
percent berry infection. At 15 0 C the virulence of C. kahawae strains was higher
than at 20 0 C and 25 0 C. Biochemical test using esterases, acid phosphatases and
alkaline phosphatases iso-enzymatic systems studied by iso-electric focusing
revealed variation among Tanzanian C. kahawae strains from those obtained from
other countries. Percent germination of conidia on wax surface extracts from green
berries of resistant coffee genotypes indicated that the wax layer influences
resistance to C. kahawae. Post-penetration growths of C. kahawae in hypocotyls
measured at 24, 48 and 72 hrs after inoculation were higher in susceptible than
resistant genotypes. Histological characterization of coffee genotypes revealed
inhibition of fungal growth by callose formation around intracellular hyphae in
resistant genotypes. Expression of coffee resistance to C. kahawae varied with the
test isolates and the hybrids. However, coffee genotype 20498 (L2) showed the
highest level of resistance to C. kahawae.
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Keywords
Colletotrichum kahawae, Coffee growing, Arabica coffee, Resistant arabica coffee, Coffee varieties, Tanzania
Citation
Kilambo, D.L. (2008). Virulence of colletotrichum kahawae strains and their effect on resistant arabica coffee varieties in Tanzani. Morogoro : Sokoine University of Agriculture