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Title:   Author  item
                                            Rayamajhi, Minitem
                                            Wheeler, Gregoryitem
                                            Pratt, Paulitem
                                            Center, Ted
  Submitted to: American Phytopathological Society
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 5/6/2010
                                    Publication  Date: 8/8/2010
                                    Citation: Rayamajhi, M.B., Wheeler, G.S., Pratt, P.D., Center, T.D. 2010. Melaleuca quinquenervia plants differ in susceptibility towards fungus Puccinia psidii infection and disease development.. American Phytopathological Society.Interpretive Summary: A rust fungus attacks immature healthy foliage melaleuca, an invasive plant in southern Florida, U.S.A. Among a group of melaleuca plants grown under same growing conditions some become susceptible while others’ become resistant towards this fungus. We assumed this difference may be due to the variability in the terpenes contained in melaleuca plants. We tested this assumption by using screenhouse and field-grown melaleuca plants. We grew melaleuca plants, tagged and inoculated with rust fungus spores, placed in screenhouse under rust fungus diseased trees and evaluated for symptoms during a 4-wk period. We also determined two major types of terpenes (viridifloral and nerolidol) in plants and distilled to obtain crude extracts.  We assessed their effects on uredospore germination. Overall, the percentage of seedlings that developed pustules (susceptible), halos only (resistant) and no halos or pustules (immune) were 63, 34, and 3, respectively; these trends were similar among field grown plants as well. Terpenes from neither nerolidol nor viridifloral types of plants inhibited uredospore germination. Gas chromatography of the crude extracts from susceptible plants showed significant increase in concentrations of total terpenes and some of their constituents (myrcene, limonene and Beta-caryophyllene) compared with similar extracts from resistant plants. These results suggest that the distilled plant extracts should be further investigated to determine their possible role in development of disease in melaleuca though they did not affect spore germination.
                                Technical Abstract: Puccinia psidii (rust fungus) attacks immature healthy foliage of Melaleuca quinquenervia (melaleuca), an invasive plant in southern Florida, U.S.A. Melaleuca plants grown under same growing conditions manifest either susceptible or resistant reactions towards this fungus. We hypothesize that the variable reactions may be due to the differences in terpenoid contents in melaleuca. This hypothesis was tested using screenhouse and field-grown melaleuca plants. Melaleuca seedlings were tagged, grown to ca 45-cm height, inoculated with uredospores, placed in screenhouse under rust-fungus infected trees and evaluated for symptoms during a 4-wk period. Plants were also evaluated for major terpenoid (viridifloral and nerolidol) content. Crude extracts of the two major terpenoids were obtained and tested for effects on uredospore germination. The percentage of seedlings that developed pustules (susceptible), halos only (resistant) and no halos or pustules (immune) were 63, 34, and 3, respectively; these trends were similar among field grown plants as well. Terpenoids from neither nerolidol nor viridifloral types of plants inhibited uredospore germination. Gas chromatography of the extracts from susceptible plants showed significant increases in concentrations of total terpenoids and some of their constituents (myrcene, limonene and Beta-caryophyllene) compared with similar extracts from resistant plants. These results suggest that terpenoids and other compounds in the distilled extract should be further investigated to determine their possible role in development of rust-fungus disease in melaleuca though they did not affect spore germination.


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