Differential contribution of the two major polygalacturonases from Penicillium digitatum to virulence towards citrus fruit

• Published in: International journal of food microbiology 2018-10, Vol.282, p.16-23
• Main Authors: Vilanova, Laura, López-Pérez, Mario, Ballester, Ana-Rosa, Teixidó, Neus, Usall, Josep, Lara, Isabel, Viñas, Inmaculada, Torres, Rosario, González-Candelas, Luis
• Format: Article
• Language: English
• Subjects: Acids; Citrus fruits; Fruits; Fungi; Galacturonic acid; Green mould; Inoculation; Lesions; Maceration; Mutants; Pathogens; Pathology; Pectinase; Penicillium digitatum; Pg2 gene; pH, orange fruits; Polygalacturonase; Post-harvest decay; Postharvest pathology; Virulence
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2018.05.031

The fungus Penicillium digitatum is the causal agent of the citrus green mould, the major postharvest diseases of citrus fruit. Lesions on the surface of infected fruits first appear as soft areas around the inoculation site, due to maceration of fruit. The macerating activity has been associated with pectinases secreted by the fungus during infection. In order to evaluate the contribution to virulence and macerating activity of the two major polygalacturonases (PGs) secreted by P. digitatum, we have obtained and characterized mutants lacking either pg1 or pg2, the genes encoding PG1 and PG2, respectively. Disease incidence of deletants in either gene was not different from that of the parental strain or ectopic transformants. However, disease progressed more slowly in deletants, especially in those lacking the pg2 gene. The lesions originated by the Δpg2 deletants were not as soft and the pH was not as acid as those originated by either the wild type strain or the ectopic transformants. Total PG activity in the macerated tissue was also lower in fruits infected with the Δpg2 deletants. Interestingly, the macerated tissue of oranges infected with Δpg2 deletants showed around 50% reduction in galacturonic acid content with respect to lesions caused by any other strain. •P. digitatum mutants lacking either pg1 or pg2 genes were obtained.•Mutants showed lower disease severity in oranges than wild type, especially in pg2 deletants.•∆pg2 showed higher decayed tissue firmness and lower galacturonic acid production.•Optima pH required by both PG activities was at least between 3.0–3.2