Morphocultural and aggressiveness variability of Colletotrichum kahawae isolates from different altitudes of the Western highlight zone of Cameroon

Abstract

Coffee berry disease (CBD) caused by Colletotrichum kahawae, is the main disease that affects arabica coffee production in Africa. A study was carried out in the West Region of Cameroon from June to September 2019 and 2020. Isolates of C. kahawae were isolated from infected green coffee berry sampled at three different altitudes, which include high, medium and low altitudes. Accordingly, seven representative C. kahawae isolates were isolated and identified from infected green coffee berry sampled from three altitudes. Colletotrichum kahawae isolates were characterized for colony colour, mycelia radial growth rate and appearance in case of cultural character, while conidia shape, size and sporulation rate in case of morphological characteristic. To characterize the aggressiveness of C. kahawae isolates, the disease severity and the days of first symptoms appearance were assessed on inoculated green coffee berry. There were significant variation among isolates related their Morphocultural and aggressiveness features. All C. kahawae isolates had cottony mycelia appearance, with four types of colony colours identified as grey, whitish, greyish and pinkish. Mycelia radial growth rate of isolates varied significantly in range from 4.32 to 7.11 mm/day. Isolates from high and medium altitude were dominated by cylindrical conidia shapes with round at both ends, followed by cylindrical acute at one and round at the other ends. While, fusiform and reniform conidia shapes were produced by isolate from low altitude. Conidia size and sporulation rate of C. kahawae isolates also differs significantly and increased with altitude. Conidia size ranged from 3.82 to 13.46 μm in length and from 1.13 to 1.69 μm in width, while sporulation rate varied from 169.06 × 104 to 438.36 × 104 conidia/ml. These parameters were strongly and positively correlated with the aggressiveness test that revealed significant variation among isolates according to their altitude origin. Isolates from high altitude were more aggressive, followed by isolates from medium altitude; whereas isolates from low altitude were less aggressive. In all, this study highlights some variations in morphocultural and aggressiveness characteristics of C. kahawae isolates with respect to altitude.