Genetic diversity and pathogenic characteristics of Phomopsis asparagi obtained from Asparagus officinalis and A. kiusianus in Japan

Phomopsis asparagi has been reported as a serious disease, causing stem blight on asparagus cultivars (Asparagus officinalis), and this fungus was also recorded as a common spot disease on wild asparagus (A. kiusianus). In this study, isolates of P. asparagi obtained from A. officinalis and A. kiusianus in different locations of the Kyushu island were successfully assessed the genetic variation through mycelial compatibility grouping (MCG) and random amplified polymorphic DNA (RAPD). Thirty fungal isolates were identified into six MCGs; of these, fifteen isolates were representatively chosen for the RAPD analysis, pathogenicity and extracellular enzyme test. Eight RAPD primers, B62, B66, B68, B71, C83, D22, D32 and E10, generated 100 different patterns from the isolates with 91% of the polymorphic bands. Based on RAPD analysis, P. asparagi isolates were divided into 3 distinct genetic clusters, namely RAPD-I, RAPD-II and RAPD-III at a similarity of 73%. The result indicated that there was a great genetic variation within the isolates from A. kiusianus, presenting in the three clusters. While the isolates from A. officinalis showed high genetic homology and they belonged to the RAPD-II cluster. There is no conflict between genetic clusters distinguished by the RAPD markers and those of MCG. On the other hand, the pathogenicity test revealed that the isolates of RAPD-II and RAPD-III were highly virulent pathogens. In contrast, the isolates of RAPD-I were weak virulent pathogens when inoculated on A. officinalis. Screening of extracellular enzyme activities concluded that all isolates were positive for laccase, lipase and protease activity.