In this review, we present a critical analysis of the current status of wild Lactuca L. germplasm in relation to its utility for lettuce breeding. We discuss wild Lactuca germplasm in ex situ collections from the perspectives of taxonomy, biogeography, biology and ecology, gene pools, field exploration and acquisition, descriptor development, characterization and evaluation, and enhancement. Future research and other activities related to wild Lactuca germplasm and their continued exploitation in lettuce breeding are considered.
SummaryDetailed studies of the infection processes of Oidium neolycopersici (tomato powdery mildew) and plant tissue responses were carried out on 10 Lycopersicon spp. accessions and one of each species of Cucumis sativus, Datura stramonium, Lactuca sativa, Petunia hybrida and Pisum sativum with different levels of resistance. Germination of O. neolycopersici conidia was not inhibited by the host plant. However, in the early stages of O. neolycopersici infection significant differences in conidial germ tube development on resistant and susceptible plant lines were observed. The first substantial differences appeared after 24 h post inoculation (hpi). Mycelia and conidiophores developed on susceptible lines; however, there was no mycelial development on resistant plant lines. The most frequent resistant response in Lycopersicon species was the necrotic (hypersensitive) reaction (HR), occasionally followed by pathogen development. The completely resistant accession L. hirsutum (LA 1347) showed only a limited number of necrotic host cells per infection site (2%). In Oidium resistant tomato lines OR 4061 and OR 960008 the existence of adult resistance was detected. This phenomenon occurred mainly in accession OR 4061. Rapid development and profuse sporulation of O. neolycopersici was observed on juvenile plants (6–8 wk old), however this was in contrast to the slow development and sporadic sporulation observed on 4 month old plants. Evidence of posthaustorial resistance was observed in the interaction of O. neolycopersici with non‐host species (Lactuca sativa and Pisum sativum.) This was in contrast to Datura stramonium and Petunia hybrida, where development of powdery mildew was delayed at a later stage in the infection cycle. With the exception of Pisum sativum, the necrotic (hypersensitive) response was observed often.
Various genetic and physiological aspects of resistance of Lycopersicon spp. to Oidium neolycopersici have been reported, but limited information is available on the molecular background of the plant-pathogen interaction. This article reports the changes in nitric oxide (NO) production in three Lycopersicon spp. genotypes which show different levels of resistance to tomato powdery mildew. NO production was determined in plant leaf extracts of L. esculentum cv. Amateur (susceptible), L. chmielewskii (moderately resistant) and L. hirsutum f. glabratum (highly resistant) by the oxyhaemoglobin method during 216 h post-inoculation. A specific, two-phase increase in NO production was observed in the extracts of infected leaves of moderately and highly resistant genotypes. Moreover, transmission of a systemic response throughout the plant was observed as an increase in NO production within tissues of uninoculated leaves. The results suggest that arginine-dependent enzyme activity was probably the main source of NO in tomato tissues, which was inhibited by competitive reversible and irreversible inhibitors of animal NO synthase, but not by a plant nitrate reductase inhibitor. In resistant tomato genotypes, increased NO production was localized in infected tissues by confocal laser scanning microscopy using the fluorescent probe 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate. NO production observed in the extracts from pathogen conidia, together with elevated NO production localized in developing pathogen hyphae, demonstrates a complex role of NO in plant-pathogen interactions. Our results are discussed with regard to a possible role of increased NO production in pathogens during pathogenesis, as well as local and systemic plant defence mechanisms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.