Optimization of cultural conditions for pectinase production by <i> Diaporthe</i> isolate Z1-1N and its pathogenicity on kiwifruit

<i>Diaporthe</i> Z1-1N, the primary causal agent of soft rot disease in kiwifruit, exhibited higher pectinase activity compared to cellulase activity in both <i>in vitro</i> and <i>in vivo</i> incubation models. To gain deeper insights into the role of pectinases in the pathogenicity of this fungus, we evaluated the effects of incubation temperature (ranging from 18 to 38 °C), duration (1 to 7 days), and medium pH (4.0 to 9.0) on the activities of two crucial pectinases: polygalacturonase (PG) and polymethylgalacturonase (PMG). Our single-factor experiments revealed that the optimal conditions for maximizing PMG yield were a pH of 7.5 and a temperature of 28 °C, with peak activity occurring after three days of incubation. Notably, PG activity peaked on the fourth day under the same pH and temperature conditions. Under the optimal conditions identified through an orthogonal experimental design, PMG exhibited higher activity than PG. Further analysis showed that temperature was the most influential factor on PMG activity, followed by incubation duration and pH. The lesion size caused by the purified pectinase extracts was 50% the lesion size that caused by the fungal mycelium of <i>Diaporthe</i> Z1-1N. These findings underscore the significance of PG and PMG as key virulence factors in the pathogenicity of <i>Diaporthe</i> Z1-1N, providing a solid scientific basis for future research into the functions of these enzymes.