Biology and molecular interactions of Parastagonospora nodorum blotch of wheat

Parastagonospora nodorum is one of the important necrotrophic pathogens of wheat which causes severe economical loss to crop yield. So far, a number of effectors of Parastagonospora nodorum origin and their target interacting genes on the host plant have been characterized. Since targeting effector-sensitive gene carefully can be helpful in breeding for resistance. Therefore, constant efforts are required to further characterize the effectors, their interacting genes, and underlying biochemical pathways. Furthermore, to develop effective counter-strategies against emerging diseases, continuous efforts are required to determine the qualitative resistance that demands to screen of diverse genotypes for host resistance. Stagonospora nodorum blotch also refers to as Stagonospora glume blotch and leaf is caused by Parastagonospora nodorum. The pathogen deploys necrotrophic effectors for the establishment and development on wheat plants. The necrotrophic effectors and their interaction with host receptors lead to the establishment of infection on leaves and extensive lesions formation which either results in host cell death or suppression/activation of host defence mechanisms. The wheat Stagonospora nodorum interaction involves a set of nine host gene-necrotrophic effector interactions. Out of these, Snn1-SnTox1, Tsn1-SnToxA and Snn-SnTox3 are one of the most studied interaction, due to its role in the suppression of reactive oxygen species production, regulating the cytokinin content through ethylene-dependent wayduring initial infection stage. Further, although the molecular basis is not fully unveiled, these effectors regulate the redox state and influence the ethylene biosynthesis in infected wheat plants. Here, we have discussed the biology of the wheat pathogen Parastagonospora nodorum, role of its necrotrophic effectors and their interacting sensitivity genes on the redox state, how they hijack the resistance mechanisms, hormonal regulated immunity and other signalling pathways in susceptible wheat plants. The information generated from effectors and their corresponding sensitivity genes and other biological processes could be utilized effectively for disease management strategies.

Ethylene-Cytokinin Interaction Determines Early Defense Response of Wheat against Stagonospora nodorum Berk

Ethylene, salicylic acid (SA), and jasmonic acid are the key phytohormones involved in plant immunity, and other plant hormones have been demonstrated to interact with them. The classic phytohormone cytokinins are important participants of plant defense signaling. Crosstalk between ethylene and cytokinins has not been sufficiently studied as an aspect of plant immunity and is addressed in the present research. We compared expression of the genes responsible for hormonal metabolism and signaling in wheat cultivars differing in resistance to Stagonospora nodorum in response to their infection with fungal isolates, whose virulence depends on the presence of the necrotrophic effector SnTox3. Furthermore, we studied the action of the exogenous cytokinins, ethephon (2-chloroethylphosphonic acid, ethylene-releasing agent) and 1-methylcyclopropene (1-MCP, inhibitor of ethylene action) on infected plants. Wheat susceptibility was shown to develop due to suppression of reactive oxygen species production and decreased content of active cytokinins brought about by SnTox3-mediated activation of the ethylene signaling pathway. SnTox3 decreased cytokinin content most quickly by its activated glucosylation in an ethylene-dependent manner and, furthermore, by oxidative degradation and inhibition of biosynthesis in ethylene-dependent and ethylene-independent manners. Exogenous zeatin application enhanced wheat resistance against S. nodorum through inhibition of the ethylene signaling pathway and upregulation of SA-dependent genes. Thus, ethylene inhibited triggering of SA-dependent resistance mechanism, at least in part, by suppression of the cytokinin signaling pathway.

Septoria blotch epidemic process on spring wheat varieties

The Septoria blotch of spring wheat leaves and ears is one of the most economically significant infections in the Siberian region. In the control systems of Septoria blotch the main ecologically safe element is resistant varieties, which are designed to slow down the pathogens reproduction rate and slow down or stop the development of the epiphytotic process. The purpose of the work was to clarify the species composition of Septoria blotch pathogens for West Siberian regions and spring wheat varieties, to study the epiphytotic process of Septoria differentially on the leaves and ears of varieties, and to evaluate the activity of seed transmission of Parastagonospora nodorum. Studies were carried out in 2016-2018 according to generally accepted methods. Septoria leaf and ear blotch of spring wheat is widespread in West Siberia and the Trans-Urals, causing a decrease in yield by up to 50 % or more with the deterioration in grain quality. The causative agents of the disease are P. nodorum, Septoria tritici, and P. avenae f. sp. triticae, and the species ratio varied across the regions and varieties, and within plant organs. In Novosibirsk Region, P. nodorum completely dominated; S. tritici was 13.8 times less common; and P. avenae f. sp. triticae was a singleton. In Tyumen Region, the dominance of P. nodorum was disrupted in some geographic locations by S. tritici and P. avenae f. sp. triticae. In Altai Krai, P. nodorum predominated at all points studied; S. tritici and P. avenae f. sp. triticae were found everywhere, but 5.6 and 8.6 times less often, respectively. The study of spring wheat varieties of different origins has not revealed any samples immune to Septoria blotch. A differentiated manifestation of resistance to Septoria leaf and ear disease has been established. Some varieties show complex resistance, combining reduced susceptibility to Septoria leaf and ear disease. Seed infection with P. nodorum in the regions of Siberia reached 7 thresholds and was largely (52.5 %) determined by the August weather conditions. The study of the collection of spring wheat varieties from three Siberian regions has revealed the following trend. Transmission of P. nodorum with the seeds of varieties was the most active (7.6 %) in Novosibirsk Region and somewhat weaker in Omsk Region (5.7 %). The most favorable phytosanitary situation was in Kurgan Region, where varieties transmitted P. nodorum to a low degree (2.1 %), below the threshold.