Submitted to: Mycological Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/15/2003
Publication Date: 6/26/2003
Citation: KOTHERA, R.T., KEINATH, A.P., DEAN, R.A., FARNHAM, M.W. AFLP ANALYSIS OF A WORLDWIDE COLLECTION OF DIDYMELLA BRYONIAE. MYCOLOGICAL RESEARCH. 2003. v.107.p.297-304 Interpretive Summary: Gummy stem blight is a destructive disease of cucurbit crops including cucumber, melon, and squash that occurs throughout the world. The disease causes damage to leaves and reduces yields of infected crops. The occurrence of gummy stem blight results in significant loss of income by cucurbit growers. Although one fungi called Didymella is known to cause gummy stem blight, other fungi are often found on infected plants and these other fungi are sometimes confused with Didymella. In this research, samples of only Didymella were collected from all over the world and they were compared at the gene or DNA level to determine if the different samples are genetically related to one another and to help devise methods to readily identify the most destructive forms. The results indicated that the different samples of Didymella could be categorized into two groups. Only one group causes a high level of disease on cucurbits. The second group causes little or no disease. Results of this research provide valuable information about the true causal agent of a serious cucurbit disease and its distribution throughout the world. This information will help agricultural scientists develop more effective measures that growers can use to minimize cucurbit crop losses due to the gummy stem blight disease.
Technical Abstract: Didymella bryoniae (anamorph Phoma cucurbitacearum) is an Ascomycete fungus that causes gummy stem blight, a foliar disease that occurs on cucurbits in greenhouses and fields throughout the world. In a previous study using RAPD analysis, little genetic diversity was found among isolates of D. bryoniae from New York and South Carolina, United States. Here we report the use of amplified length polymorphism (AFLP) analysis to assess the genetic variation within a worldwide collection of D. bryoniae. A total of 102 field and greenhouse isolates from ten states in the USA (California, Delaware, Florida, Georgia, Indiana, Maryland, Michigan, Oklahoma, South Carolina, and Texas) and seven other countries (Australia, Canada, China, Greece, Israel, Sweden, The Netherlands) were examined. Seven different AFLP pimer-pair combinations generated 450 bands, of which 134 were polymorphic (30%). Using cluster analysis, two groups and a total of seven subgroups were delineated. Representative isolates from group two were less virulent on muskmelon and watermelon seedlings than isolates from group one. Isolates from northern states within the United States grouped separately from isolates originating from the southern United States.