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Characterization of resistance to Puccinia hemerocallidis in daylily cultivars
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Resumo(s)
Hemerocallis, also called daylily, is a perennial ornamental plant which is easy to cultivate. However,
rust caused by Puccinia hemerocallidis has gradually become a global disease of daylily cultivars. In
recent years, daylily rust has appeared on daylilies grown in Europe, seriously affecting their
ornamental value. The objectives of this study are to evaluate the response of European daylily
cultivars to rust, to explore the relationship between their ploidy and rust resistance, and to observe the
interaction of resistant and susceptible cultivars with rust at the histological level. Eighteen European
daylily cultivars were evaluated to observe their response. After inoculation with uredospores of P.
hemerocallidis (isolate Ph02), two of them were evaluated as resistant; three were evaluated as
moderate resistant; the rest were evaluated as susceptible. Among these cultivars, diploid tend to be
more likely to have resistance to rust than tetraploid ones. The incubation period of rust on these
cultivars is from 5 to 8 days, and the latent period is from 7 to 14 days after inoculation. The
susceptible cultivar ‘Carla's Pretty’ and the resistant cultivar ‘Flore Pleno’ were used for histological
analysis. The uredospores germinated and differentiated appressoria over stomata in both cultivars.
However, in the cultivar ‘Flore Pleno’ the fungus stopped growing before haustorium formation. This
pre-haustorial resistance was associated with the early accumulation of phenolic compounds and the
deployment of hypersensitive-like response (HR), and macroscopic symptoms were not visible.
Reversely, in the susceptible cultivar, the fungus colonized the leaves without apparent inhibition,
producing intercellular hyphae and haustoria within the mesophyll cells and sporulation.
The results from the two parts of the experiment showed that the use of resistant cultivars could be a
good method to control daylily rust. The cultivar ‘Stella d’Oro’, as ‘Flore Pleno’, did not show
symptoms affecting the ornamental value after being inoculated with rust, the mechanisms of their
resistance to rust and the gene that triggers the resistance are valuable and need to be further studied.
Plants included in genus Hemerocallis, commonly known as daylilies, are popular ornamental plants worldwide because of the large, conspicuous flowers and their adaptation to a wide range of soils and climates. They have a history of traditional use in medicine, food, and ornamentation, and they are widely cultivated in Asia, Europe, and North America. Daylily rust, caused by Puccinia hemerocallidis, has become an increasing problem for daylily growers. Initially confined to Eastern Asia, the disease spread to Oceania, Africa, the Americas, and Portugal in the 21st century gaining a worldwide distribution. P. hemerocallidis is a macrocyclic fungus, with Hemerocallis spp. as the uredinial/telial hosts. The disease symptoms are the typical rust symptoms, with leaves (both sides) showing bright orange spots corresponding to uredosporic sori, leading to necrosis and senescence. Telial sori appear as dark brown pustules in the autumn. The aecial hosts (Patrinia spp.) are basically restricted to Eastern Asia, meaning that elsewhere the disease cycle is limited to the uredosporic cycle. The rust resistance of Hemerocallis cultivars in Europe and the mechanisms of resistance are not well understood. In this study, the severity and resistance of daylily cultivars infected by rust were evaluated by measuring the area of symptoms by Winfolia software, using sporulation, type of response to P. hemerocallidis and whole disease area as standards to evaluate the resistance of each cultivar. Light microscopy was used to evaluate the infection process of P. hemerocallidis and the responses it induced on the daylily-resistant cultivar ‘Flore Pleno’, comparatively with the susceptible cultivar ‘Carla’s Pretty’. Symptoms of inoculated leaves were analyzed to evaluate the resistance of eighteen European daylily cultivars to rust. Two cultivars were identified as resistant; three as moderate resistant and the remaining cultivars were considered susceptible. Among these cultivars, diploids tend to be more likely to have resistance to rust than tetraploid ones. According to data obtained, the incubation period of rust on daylily cultivars which have different rust resistance is from 5 to 8 days, and their latent period is from 7 to 14 days after inoculation. In the histological observations through light microscopy, it was observed that in the majority of the infection sites, P. hemerocallidis differentiated post-penetration fungal structures, such as substomatal vesicles and intercellular hyphae, in both daylily cultivars. In the susceptible cultivar the fungus pursued the colonization of leaf tissues, producing intercellular hyphae and haustoria within the mesophyll cells, giving rise to sporulation 7 days after inoculation. In the resistant cultivar, the fungus ceased its growth before haustorium formation. The host defense responses corresponded to the early accumulation of phenolic compounds and the hypersensitive-like response. According to the results obtained, it can be said that although some daylily cultivars have effective resistance to P. hemerocallidis infection, it is undeniable that with the expansion of the application of daylily in the future, daylily rust may become a major hazard and needs to be carefully controlled. Follow-up research on the genes controlling daylily resistance to rust and the host resistance mechanisms can bring greater help for the control of this disease.
Plants included in genus Hemerocallis, commonly known as daylilies, are popular ornamental plants worldwide because of the large, conspicuous flowers and their adaptation to a wide range of soils and climates. They have a history of traditional use in medicine, food, and ornamentation, and they are widely cultivated in Asia, Europe, and North America. Daylily rust, caused by Puccinia hemerocallidis, has become an increasing problem for daylily growers. Initially confined to Eastern Asia, the disease spread to Oceania, Africa, the Americas, and Portugal in the 21st century gaining a worldwide distribution. P. hemerocallidis is a macrocyclic fungus, with Hemerocallis spp. as the uredinial/telial hosts. The disease symptoms are the typical rust symptoms, with leaves (both sides) showing bright orange spots corresponding to uredosporic sori, leading to necrosis and senescence. Telial sori appear as dark brown pustules in the autumn. The aecial hosts (Patrinia spp.) are basically restricted to Eastern Asia, meaning that elsewhere the disease cycle is limited to the uredosporic cycle. The rust resistance of Hemerocallis cultivars in Europe and the mechanisms of resistance are not well understood. In this study, the severity and resistance of daylily cultivars infected by rust were evaluated by measuring the area of symptoms by Winfolia software, using sporulation, type of response to P. hemerocallidis and whole disease area as standards to evaluate the resistance of each cultivar. Light microscopy was used to evaluate the infection process of P. hemerocallidis and the responses it induced on the daylily-resistant cultivar ‘Flore Pleno’, comparatively with the susceptible cultivar ‘Carla’s Pretty’. Symptoms of inoculated leaves were analyzed to evaluate the resistance of eighteen European daylily cultivars to rust. Two cultivars were identified as resistant; three as moderate resistant and the remaining cultivars were considered susceptible. Among these cultivars, diploids tend to be more likely to have resistance to rust than tetraploid ones. According to data obtained, the incubation period of rust on daylily cultivars which have different rust resistance is from 5 to 8 days, and their latent period is from 7 to 14 days after inoculation. In the histological observations through light microscopy, it was observed that in the majority of the infection sites, P. hemerocallidis differentiated post-penetration fungal structures, such as substomatal vesicles and intercellular hyphae, in both daylily cultivars. In the susceptible cultivar the fungus pursued the colonization of leaf tissues, producing intercellular hyphae and haustoria within the mesophyll cells, giving rise to sporulation 7 days after inoculation. In the resistant cultivar, the fungus ceased its growth before haustorium formation. The host defense responses corresponded to the early accumulation of phenolic compounds and the hypersensitive-like response. According to the results obtained, it can be said that although some daylily cultivars have effective resistance to P. hemerocallidis infection, it is undeniable that with the expansion of the application of daylily in the future, daylily rust may become a major hazard and needs to be carefully controlled. Follow-up research on the genes controlling daylily resistance to rust and the host resistance mechanisms can bring greater help for the control of this disease.
Descrição
Mestrado em Biologia dos Recursos Vegetais. Universidade de Lisboa, Instituto Superior de Agronomia. Universidade do Porto, Faculdade de Ciências
Palavras-chave
disease resistance hemerocallis ploidy level puccinia hemerocallidis response to pathogen disease resistance hemerocallis ploidy level puccinia hemerocallidis response to pathogen
Contexto Educativo
Citação
Shan, H. Characterization of resistance to Puccinia hemerocallidis in daylily cultivars. Lisboa: ISA-Universidade de Lisboa, 2023. Dissertação de Mestrado
Editora
Instituto Superior de Agronomia, Universidade de Lisboa