Morphological observations. The colonies of the Colletotrichum isolates were white at the initial growing stage, turning pale gray at the later stage, with aerial mycelium sparse, hairy, sometimes producing abundant yellow-orange pionnotes (Fig.2).
There was considerable variation in mycelial growth rate among the 136 Colletotrichum isolates (Table 4). The average mycelial growth rate for C. asianum was 0.38-1.59 cm/d, C. siamense 0.52-1.51 cm/d and C. fructicola 0.60-1.19 cm/d. Conidia were all hyaline, aseptate and long elliptic to cylindrical.
The average conidial size range for C. asianum, C. fructicola, C. siamense, C. karstii, C. endophytica, C.
scovillei and C. cliviae was 11.94-20.27×4.56-6.39 ?m, 12.29-22.79×3.72-6.07 ?m, 11.51~16.80×4.72-6.98 ?m, 9.43-15.07×3.35-6.74 ?m, 14.34-15.77×5.56-5.57 ?m, 11.79-12.60×4.12-5.25 ?m, 15.34-18.32×5.98-5.99 ?m, respectively (Table 5). The length of conidia for each isolate varied from 6.99 ?m to 29.22 ?m and the width of conidia varied from 2.99 ?m and 9.85 ?m (Table 5). Calculated for each isolate grown on PDA, the mean conidial of length and width were ranged from 11.51 ?m to 25.54 ?m and 3.96 ?m to 8.22 ?m, respectively.
The conidial morphology of Colletotrichum species in mango differed significantly between and within species. For examples, C. fructicola (GZ15-1) have profuse sporulation, C. gigasporum (HN42-2) produce the largest spores, and the shortest spores generated by C. scovillei (YN51-1). Conidial appressoria were pale black, brown to dark brown, nearly elliptical or irregular, edges complete.
The length of appressoria for each species varied from 4.92 ?m to 14.94 ?m and the width of appressoria varied from 3.61 ?m and 10.63 ?m (Table 6). The mean value of length and width calculated for each isolate ranged from 6.38 ?m to 12.41 ?m. Mycelial appressoria were pale brown to dark brown, rod-shaped, occasionally irregular, edge complete. The length of appressoria for each species varied from 5.55 ?m to 20.70 ?m and the width of appressoria varied from 3.53 ?m and 15.36 ?m. The mean value of length and width calculated for each isolate ranged from 7.55 ?m to 14.99 ?m and 5.45 to 12.21 ?m, respectively.
The various Colletotrichum species reported here showed differences in both conidial and appressorial sizes, growth rates (Table 4, 5 and 6). Based on morphology observation and multi loci sequence analysis, 136 mango Colletotrichum isolates obtained in China can be classified into 14 species as follow: 38 isolates (27.9%) C. asianum, 38 isolates (27.9%) C. siamense. 32 isolates (23.5%) C. fructicola, 5 isolates C.
karstii (3.7%), 4 isolates C. endophytica (2.9%), three isolates C. scovillei (2.2%), two isolates C. cliviae (1.5%) and one isolate for each of the following species: C. gigasporum, C. gloeosporioides, C.
jiangxiense, C. liaoningense, C. musae, C. tropicale and C. cordylinicola.
Furthermore, seven isolates listed in this study were not aligned with any registered/reported Colletotrichum species and further research will be required in the future. This is the first report for karstii, C. endophytica, C. scovillei, C. cliviae, C. gigasporum, C.
gloeosporioides, C. jiangxiense, C. liaoningense, C. musae, C.
tropicale, C. cordylinicola causing mango anthracnose in China. This is also the first report for C. scovillei, C. endophytica, C. gigasporum, C.
jiangxiense, C. liaoningense, C. musae and C. cordylinicola associating with mango anthracnose worldwide. Provincial geographic distribution of Colletotrichum species on mango in China.
The diversity of species and geographical distribution for various Colletotrichum species causing mango anthracnose across different provinces in China were shown in Fig.3. Hainan and Yunnan had the most abundant and diverse Colletotrichum species on mango. Nine Colletotrichum species (C. asianum, C. siamense, C. fructicola, C.
karstii, C. scovillei, C. endophytica, C. cordylinicola, C. tropicale and C. gigasporum) were responsible for mango anthracnose in Hainan province whilst eight species (C.
asianum, C. siamense, C. fructicola, C. karstii, C.
scovillei, C. endophytica, C. cliviae and C. liaoningense) were pathogenic for mango anthracnose in Yunnan. Five species (C. fructicola, C.
karstii, C. jiangxiense, C. gloeosporioides and C. musae) were associated with mango anthracnose in Guizhou province. Only two Colletotrichum species (C. asianum and C.
siamense) were isolated in Sichuan and Guangdong provinces, respectively. C. asianum and C. fructicola were found in Fujian province. As a whole, C. asianum, C.
siamense, C. fructicola were the dominant species wide spread across the major mango growing areas in southern China. Pathogenicity and virulence in tissues. All 136 tested isolates were pathogenic to mango leaves and fruits.
The virulence of the tested isolates on mango fruits was significantly different. The virulence of the tested strains in mango fruit differed considerably because the diameters of disease lesions varied from 0.57 cm to 4.34 cm. According to the diameter size of the disease spots, the virulence scale can be classified as strongly virulent (? 2 cm), moderately virulent (? 1.0 to < 2 cm) and weakly virulent (< 1.0 cm). Out of all the 136 isolates investigated, 71 (52%) isolates were moderately virulent, 9 (7%) isolates were strongly virulent, 56 (41%) isolates were weakly virulent.
The least virulent strain was C. siamense SC16, while the most virulent strain was C. siamense GD7-1. The virulence of the tested isolates on mango leaves was also significantly different, and the diameters of disease lesions varied from 0.57 cm to 4.34 cm. The virulence of the tested strains in mango differed considerably.
According to the diameter size of the disease lesions, the virulence scale can be classified as strongly virulent (? 2 cm), moderately virulent (? 1.0 to < 2 cm) and weakly virulent (< 1.0 cm). Using this scale, 89 isolates (65%) were moderately virulent, 39 isolates (29%) were strongly virulent, 8 isolates (6%) were weakly virulent. The least virulent strain was Colletotrichum. sp FJ31-1, while the most virulent strain was C.
siamense SC2-1.
