Pathogenic and biological characterisation of T-DNA insertional mutants of a Colletotrichum gloeosporioides casual organism of apple anthracnose

Anthracnose leaf spot caused by Colletotrichum gloeosporioides is an important disease of apples, resulting in serious damage to the fruit production. In this paper, the pathogenic and physiological characters of sixteen isolates and the wild isolate "Stj16" were studied. In the current study, we generated C. gloeosporioides strains expressing green fluorescence by introducing a GFP gene via an Agrobacterium tumefaciens-mediated transformation (ATMT). To confirm the subcellular localisation of the A2799 gene, an A2799gfp fusion expression mutant was constructed. After observation of the fusion expression, the A2799gfp fusion expression protein was located in the peroxisomes of the cell. The pathogenicity results showed that the mutants A4204, M44, A1919, A3638 and A1598 lost the pathogenic capability and virulence, however, the virulence of the mutants A1764, A439, A3885, G1183, A3144, A1649 and A2675 increased significantly to the apple fruits compared to the wild isolate "Stj16". The biological study indicated that a Rose Bengal Agar (RBA) medium decreased the mycelium growth, but it can increase the sporulation for most of the isolates. The mutant A4204 does not grow well at pH 4.0 and pH 8.0, and mutant M44 just has the optimum growth at pH 8.0, and a 12 h light and 12 h dark condition stimulates the sporulation for most of the tested mutants, but the A1764 mutant more sporulated at regular dark conditions. All the mutants and "Stj16" grew vigorously at 25 °C-30 °C, for "Stj16", it produced the highest number of conidia at 30 °C compared with the other temperatures. Based on the biological study, we found the best growing and sporulation conditions for all the tested isolates. The information generated in the present study will facilitate molecular research on this devastating fungus.