CULTURAL CHARACTERIZATION OF COLLETOTRICHUM GLOEOSPORIOIDES, THE CAUSAL AGENT OF CITRUS DIEBACK

Abstract

Citrus dieback caused by Colletotrichum gloeosporioides, is one of the major constrains in citrus production in Pakistan. To manage this disease, a comprehensive study of its pathogen is important. The present study is therefore conducted to investigate the effect of different culture media such as potato dextrose agar (PDA), bean extract agar (BEA), malt and yeast extract agar (MYEA) and five pH levels 5.0, 5.5, 6.0, 6.5 along with unamended control on growth and sporulation of the fungus. Culture characters of the fungus varied according to culture media. It forms fluffy and dense culture on PDA media while flat and sparse colonies on BEA and MYEA media. Colony diameter of the fungus was also significantly different for culture media. It was measured from underside of the petri plates, using a transparent scale. Measurement was made along two perpendicular lines and their mean was recorded. The highest mean colony diameter (5.98cm) was observed on MYEA, followed by BEA (5.88cm) and the lowest (5.72cm) on PDA. Conversely, higher mycelium weight (429.2 mg) of the fungus was achieved on PDA medium, followed by BEA (397.4 mg) and the lowest on MYEA (351.8 mg). Moreover, pH level 6.5 showed highest colony diameter (6.038cm). Highly significant variations among the culture media or pH levels and or the interaction of the two were observed for spore concentration. The greatest spore concentration (705.6 thousands/ml) was achieved on MYEA medium followed BEA and PDA. Similarly, highest spore concentration (1346 thousands spores/ml) was achieved at pH 6.0 on MYEA medium. In other media, the pH did not show significant differences. The mean values of spore concentrations of C. gloeosporioides at different pH level were however, significantly different with the highest at pH 6.0 (501.3) and the lowest at pH 5.5 (124).