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Variations in cultural, morphological and molecular characteristics, and aggressiveness of different isolates of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc., causal organism of anthracnose on mango (Mangifera indica L. cv. Carabao)
Thesis Abstract:
Fifty-six pathogenic isolates of Colletotrichum gloeosporioides were isolated from mangoes cv. ‘Carabao’ in different locations of the Philippines. The isolates were grouped based on their colony characteristics at five days after incubation on PDA at room temperature. The variations of the pathogen were done based on cultural and morphological characteristics, and their aggressiveness across different locations. Sequences of the rDNA internal spacer region (ITS) of the isolates were also analyzed to determine the variation and grouping based on molecular aspect.
Significant differences of growth rate were found among isolates from different locations (p < .05). The highest growth rate was found in the isolates from Los Baños, Laguna (16.95 mm/day), while Cebu City and Pangasinan had the slowest growth with just only slightly less or more than 5 mm/day. Different characteristics of colonies were observed throughout different locations. The majority of colony’s characteristics were found as greenish grey, fluffy, raised, medium dense, and with formation of acervuli. Based on colony characteristics, seven groups of C. gloeosporioides isolated mangoes cv. ‘Carabao’ from different locations in the Philippines.
The conidia varied in size across locations. The conidia dimensions of the isolates were 12.5–23.3 × 3–7.2 μm, and significantly different (p < .05) across locations. The isolates from Davao City produced small conidia, whereas the biggest conidia were found from Calamba, Laguna isolates.
Different aggressiveness were observed in different locations, in which the isolates from Davao City were the most virulent. Slow or fast growth of the isolates on PDA did not affect their virulence on inoculated fruits (R<sup>2</sup> = 0.007) even though positive relationship was found in incubation period of the isolates (R<sup>2</sup> = 0.203).
Bootstrap test of phylogeny using UPGMA analysis of the ITS sequences classified all of the isolates into three major clades. Clade I had the highest proportion of about 95 percent of the total population. It was classified into two groups and each group was subdivided into two subgroups. No significant relationship between colony characteristics and ITS region-sequenced molecular groupings of C. gloeosporioides was found in this study (p = .12). Neither relationship was seen between the three major geographical origins of the Philippines and molecular grouping. However, if the data was performed in small locations at the municipality level, highly significant relationship was found (p = .005) by Fisher’s exact test.