Abstract
The destructive wheat powdery mildew disease is caused by the fungal pathogen Blumeria graminis f. sp. tritici (Bgt). PmG3M, derived from wild emmer wheat Triticum dicoccoides accession G305-3M, is a major gene providing a wide-spectrum resistance against Bgt. PmG3M was previously mapped to wheat chromosome 6B using an F6 recombinant inbred line (RIL) mapping population generated by crossing G305-3M with the susceptible T. durum wheat cultivar Langdon (LDN). In the current study, we aimed to explore the defense mechanisms conferred by PmG3M against Bgt. Histopathology of fungal development was characterized in artificially inoculated leaves of G305-3M, LDN, and homozygous RILs using fluorescence and light microscopy. G305-3M exhibited H2O2 accumulation typical of a hypersensitive response, which resulted in programmed cell death (PCD) in Bgt-penetrated epidermal cells, while LDN showed well-developed colonies without PCD. In addition, we observed a post-haustorial resistance mechanism that arrested the development of fungal feeding structures and pathogen growth in both G305-3M and resistant RIL, while LDN and a susceptible RIL displayed fully developed digitated haustoria and massive accumulation of fungal biomass. In contrast, both G305-3M and LDN exhibited callose deposition in attempt to prevent fungal invasion, supporting this as a mechanism of a basal defense response not associated with PmG3M resistance mechanism per se. The presented results shed light on the resistance mechanisms conferred by PmG3M against wheat powdery mildew.
Highlights
Powdery mildew diseases of plants are widespread in temperate climates and are a continuous threat to agriculture as they evolve quickly to overcome plant resistance [1]
We found that a post-haustorial resistance mechanism was activated by PmG3M, leading to arrest of the development of fungal feeding structures and termination of growth of the fungal biomass on the leaf surface
Disease Assessment of Wheat Powdery Mildew at 3 days post inoculation and small B. graminis f. sp. tritici (Bgt) colonies became visible to the naked eye at 4 dpi
Summary
Powdery mildew diseases of plants are widespread in temperate climates and are a continuous threat to agriculture as they evolve quickly to overcome plant resistance [1]. More than 650 species of powdery mildew fungi that can infect over 10,000 plant species were identified [2]. These plant pathogens are obligate biotrophs that can infect leaves, stems, flowers and fruits and frequently decrease the grain yield and quality of agricultural crops [1,3,4]. The infection process of the disease, during the asexual stage, includes the following steps and processes: (i) inoculation a haploid conidium of Bgt is landing on leaf of a susceptible wheat plant; (ii) germination – the spore is germinating and forming first primary germ tube(s) that would never fully penetrate into epidermal cells, and a secondary germ tube that will differentiate into an appressorial germ tube (AGT);
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