Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2006
Publication Date: 8/1/2006
Citation: Kaminski, J., Dernoeden, P., Oneill, N.R., Mischke, B.S. 2006. Genetic diversity among Ophiosphaerella agrostic strains causing dead spot in creeping bentgrass. Plant Disease. 90:146-154. Interpretive Summary: Dead Spot is a new disease of grasses that is spreading rapidly. Since its discovery in 1998 in Maryland, it has been found in 11 states. The disease is caused by a newly described species in the fungal genus Ophiosphaerella. Species in this genus belong to a very important class of fungi, many of which are serious agricultural pests that attack many crops. Little is known about the biology or genetics of these fungi, and O. agrostis in particular. O. agrostis is unusual in that it produces prodigious numbers of sexual fruiting bodies in the field throughout the summer months and has no other known spore stage. Production of fruiting bodies increases the chance for genetic recombination which provides the fungus with the capability to adapt and increase its fitness as a pathogen. In this study, we used molecular techniques to compare and identify genetic diversity among 77 strains of O. agrostis from 21 locations in 11 states. Three cultural characteristics were found that could be used to distinguish isolates. The capacity of strains of the fungus to produce the fruiting bodies that perpetuate the fungus and the disease was determined. The molecular genetic variation of O. agrostis was diverse and strains separated into three distinct groups. One strain in particular showed reduced sensitivity to fungicides. The geographic origins of the strains and the ability to produce fruiting bodies were the best indicators for genetic similarity among strains. It is important to identify strain-specific groups and to understand their biology and capacity for reproduction and variation. The strain information will be useful to the turfgrass industry and other scientists to determine the origin of the disease, prevent its spread, and develop appropriate disease control methods.
Technical Abstract: Dead Spot(Ophiosphaerella agrostis) is a relatively new disease of young creeping bentgrass and hybrid bermudagrass putting greens in the USA. Little is known about the biology or genetic diversity of the pathogen. O. agrostis is unusual in that it produces prodigious numbers of pseudothecia in the field throughout the summer months and has no known asexual stage. The objectives of this study were to: 1) identify genetic diversity among O. agrostis isolates using fluorescent AFLP DNA fingerprinting; 2) evaluate cultural characteristics that may distinguish isolates; and 3) determine individual isolates’ capacity for and rate of pseudothecia production. A total of 77 O. agrostis isolates were collected from twenty-one different creeping bentgrass or hybrid bermudagrass putting greens in eleven states. DNA fingerprint analysis revealed that 78 out of 97 markers were polymorphic (80.4%) providing 57 unique profiles. Genetic variation of O. agrostis was diverse and isolates separated into three distinct clades with 69% or greater similarity. Analysis of molecular variance indicated that the geographic origins of the isolates and the ability to produce pseudothecia were the best indicators for genetic similarity among O. agrostis isolates. Colony color varied among the isolates, but generally was similar for isolates residing within two clades (B and C). Colony color of isolates within clade A appeared to be a mixture of the colony colors exhibited by clades B and C.