Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 11, 2006
Publication Date: August 1, 2006
Citation: Pratt, R.G. 2006. Frequency and pathogenicity of Dermatiaceous hypomycetous on annual ryegrass overseeded on bermudagrass in Mississippi. Plant Disease. 90:1085-1090. Interpretive Summary: Annual ryegrass is a fall-seeded, cool-season grass that is widely grown for both forage and turf in the southeastern USA. Often ryegrass is overseeded onto bermudagrass, the most common warm-season grass, and both species may grow together simultaneously for several months in the fall and spring. Most fungal diseases of ryegrass and bermudagrass are considered to be distinct, and even when the two species are grown together, the same diseases usually are not known to affect both. In this study, diseases on leaves of annual ryegrass and bermudagrass growing simultaneously during spring on a swine waste application site were found to be caused by many of the same fungal pathogens. Of nine pathogens identified from 400 diseased leaves from each grass, one (Bipolaris cynodontis) was the most frequent on both grasses. This fungus previously was known to be a common and important pathogen of bermudagrass, but it had never been known to infect ryegrass in North America. Most of the other eight fungal pathogens also were observed on both ryegrass and bermudagrass. When Bipolaris cynodontis from both ryegrass and bermudagrass was applied to healthy leaves of ryegrass, it caused symptoms as strong as those caused by one of the well-known ryegrass pathogens with which it was compared. These results indicate that Bipolaris cynodontis may be an important pathogen of both ryegrass and bermudagrass, and that many other fungal pathogens also infect both grasses simultaneously. It is also suggested from results of this study that these fungal pathogens are likely to cross-infect from bermudagrass to ryegrass and vice versa during their periods of simultaneous growth in fall and spring.
Technical Abstract: Fungal diseases of ryegrass (Lolium multiflorum Lam.), a cool-season annual grown for forage and turf in the southeastern USA, and bermudagrass (Cynodon dactylon [L.] Pers.), a warm-season perennial, usually are distinct and do not damage both species simultaneously. In May 2002, symptoms of leaf and stem necrosis were observed simultaneously in bermudagrass and in ryegrass that had been overseeded on it the previous fall on a swine waste application site in Mississippi. Nine species of Bipolaris, Curvularia, Drechslera, and Exserohilum were observed on symptomatic leaf tissues of both species, and 10 new state, regional, continental and worldwide records of pathogen occurrence were established. B. cynodontis and D. dictyoides were the pathogens observed most frequently on ryegrass, and B. cynodontis, E. rostratum, and C. lunata were observed most frequently on bermudagrass. In excised leaves of ryegrass, most isolates of B. cynodontis from ryegrass and bermudagrass were equally virulent and caused similar or greater necrosis than isolates of D. dictyoides, a recognized ryegrass pathogen. Isolates of B. cynodontis from both hosts also caused similar severity of symptoms in foliage of ryegrass and bermudagrass plants inoculated with spores. Results demonstrate that many of the same species of dematiaceous hyphomycetes infect ryegrass and bermudagrass simultaneously when the two grasses are grown together and that B. cynodontis, an established bermudagrass pathogen, also infects ryegrass at high frequencies and is significantly virulent on it. These results indicate a strong likelihood for epidemiological relationships between diseases caused by dematiaceous hyphomycetes on bermudagrass and ryegrass overseeded upon it in the southeastern USA.