Resistance mechanisms of wild tomato germplasm to infection of Oidium neolycopersici

Abstract

Tomato powdery mildew (Oidium neolycopersici) is one of the most devastating diseases of cultivated tomatoes worldwide. Although the first epidemics were recorded more than 25 years ago many aspects of this host-pathogen interaction are still not well understood. Detailed morphological and molecular studies of the anamorphs confirmed that O. neolycopersici is phylogeneticaly close to Erysiphe aquilegiae var. ranunculi. Host range is rather broad, apart from Solanaceae hosts were found in the families Apocynaceae, Campanulaceae, Crassulaceae, Cistaceae, Cucurbitaceae, Linaceae, Malvaceae, Papaveraceae, Pedialiaceae, Scrophulariaceae, Valerianaceae a Violaceae. Non-host resistance within these families is not based on inhibition of formation of primary haustorium, however, on post-haustorial hypersensitive reponse and another type of non-hypersensitive resistance. Screening of wild Solanum species (previous Lycopersicon spp.) germplasm revealed valuable sources of resistance (S. habrochaites, S. pennellii, S. cheesmaniae, S. chilense, S. peruvianum). The main resistance mechanism was found to be a hypersensitive response (HR), in some cases followed by limited development of the pathogen. However, there is a broad variation in resistance response on the histological and cytological level. Interaction between many wild Solanum spp. and O. neolycopersici is race-specific, at least three races were differentiated. In some interspecific crosses (S. lycopersicum × S. habrochaites) adult plant resistance was observed. Biochemical studies focusing on production of reactive oxygen species (ROS) and peroxidase activity during infection of O. neolycopersici showed that production of ROS and activity of corresponding enzymes is related to activation of defence responses in genotypes of wild Solanum sect. Lycopersicon. The significance of nitric oxide (NO) in O. neolycopersici pathogenesis was supported by experiments with NO donors and scavengers. In moderately resistant genotype S. chmielewskii, treatment by heat stress caused slight deceleration of pathogen development, increased production of jasmonic acid (JA) and abscisic acid (ABA) and increased peroxidase activity in infected plants. The different degree of tomato resistance/ susceptibility did not markedly change the rate and extent of photosynthetic response to O. neolycopersici; only minimal impairment of photosynthesis was found in both susceptible and moderately resistant genotypes during the Harper Adams University, Newport, Shropshire TF10 8NB, UK first 9 days after inoculation. The accumulated evidence confirm a crucial role of localised increased production of ROS and reactive nitrogen species (RNS) in response to pathogen penetration into plant tissue and its involvement in the plant resistance responses including the initiation and progression of plant cell death in host wild Solanum species. Crucial points of further research are discussed.

Diverse responses of wild and cultivated tomato to BABA, oligandrin andOidium neolycopersiciinfection

“…This finding might be related to a generally different extent and timing of transcript induction in the susceptible and resistant tomato genotypes. In our previous studies on these tomato genotypes, we also found differences in the extent and timing of the increased production of defence signalling molecules NO and H 2 O 2 during the time-course of powdery mildew invasion (Piterkova et al, 2009;Lebeda et al, 2014). The most remarkable difference between the genotypes studied was in the PR1 and germin-like protein classes (Fig.…”

“…BABA represents a nonprotein amino acid generally accepted as a potent priming agent conferring increased resistance to biotic and abiotic stresses in many studied plants. As model tomato genotypes, we selected the previously well-characterized highly susceptible S. lycopersicum 'Amateur', representing a domesticated inbred cultivar, and S. habrochaites that exhibits a high non-specific resistance (Mieslerova et al, 2000;Tomankova et al, 2006;Piterkova et al, 2009Piterkova et al, , 2011Lebeda et al, 2014). The defence responses were monitored as transcript-level changes of selected genes with proven roles in non-specific resistance in tomato and model plants N. tabacum or A. thaliana.…”

Genetics and molecular mechanisms of resistance to powdery mildews in tomato (Solanum lycopersicum) and its wild relatives

“…Now it is believed that O. neolycopersici is present worldwide, except in Australia where O. lycopersici is the causal agent for PM disease in tomato (Kiss et al 2001(Kiss et al , 2005. Although there is not a consensus on the host range of O. neolycopersici Lebeda et al 2013), there is some evidence suggesting that this pathogen is adapted to plant species from 13 plant families (Whipps et al 1998;Jankovics et al 2008). For further information of O. lycopersici and O. neolycopersici, please see the comprehensive review by Lebeda et al (2013).…”

“…Although there is not a consensus on the host range of O. neolycopersici Lebeda et al 2013), there is some evidence suggesting that this pathogen is adapted to plant species from 13 plant families (Whipps et al 1998;Jankovics et al 2008). For further information of O. lycopersici and O. neolycopersici, please see the comprehensive review by Lebeda et al (2013).…”

“…One reason for this knowledge gap is that this obligate fungus needs to be maintained and propagated on tomato plants and, like other obligate PMs, is not easily amenable to molecular analysis (Bardin et al 2007). Moreover, its sexual stage has not been reported so far, and this hampers genetic studies on this fungus (Lebeda et al 2013). One way to compensate this shortage of knowledge is to explore the discovered mechanisms of pathogenicity in other PM species.…”