Elucidation of pectinolytic enzyme activities of a non-pathogenic watermelon pathogen mutant, Fusarium oxysporum f.sp. niveum M87

The watermelon pathogen Fusarium oxysporum f.sp. niveum Fon2 and its UV-induced non-virulent mutant M87 were evaluated for the extracellular production of polygalacturolitic enzymes. The mutant M87 was found to lack two functional exopolygalacturonases (exoPG). The exoPG proteins of the Fon2 strain had similar molecular masses of 50 kDa and 49 kDa, and showed significant homology with exoPGs of the tomato pathogen, F. oxysporum f.sp. lycopersici. Two isoforms of an endoPG were also detected in both Fon2 and M87 using SDS-PAGE. Using reverse transcriptase?polymerase chain reaction, specific oligonucleotides designed from the coding region of the exoPG genes determined to be present in Fon2 were used to investigate the presence of transcripts in the cultures grown in induction media. The presence of mRNAs of both exoPGs were detected when Fon2 and the mutant M87 were grown with pectin, sodium polygalacturonate and polygalacturonic acid as sole carbon sources, but not glucose. Expression of both exoPGs in infected watermelon seedlings was observed until plants fully developed infection symptoms with Fon2 on day 6; M87-infected plants showed no symptoms.