Pyrenophora teres: Taxonomy, Morphology, Interaction With Barley, and Mode of Control

Abstract

Net blotch, induced by the ascomycete Pyrenophora teres, has become among the most important disease of barley (Hordeum vulgare L.). Easily recognizable by brown reticulated stripes on the sensitive barley leaves, net blotch reduces the yield by up to 40% and decreases seed quality. The life cycle, the mode of dispersion and the development of the pathogen, allow a quick contamination of the host. Crop residues, seeds, and wild grass species are the inoculum sources to spread the disease. The interaction between the barley plant and the fungus is complex and involves physiological changes with the emergence of symptoms on barley and genetic changes including the modulation of different genes involved in the defense pathways. The genes of net blotch resistance have been identified and their localizations are distributed on seven barley chromosomes. Considering the importance of this disease, several management approaches have been performed to control net blotch. One of them is the use of beneficial bacteria colonizing the rhizosphere, collectively referred to as Plant Growth Promoting Rhizobacteria. Several studies have reported the protective role of these bacteria and their metabolites against potential pathogens. Based on the available data, we expose a comprehensive review of Pyrenophora teres including its morphology, interaction with the host plant and means of control.

Keywords: Hordeum vulgare L.; Pyrenophora teres; barley; net blotch; plant growth promoting rhizobacteria.

Figure 1

Phylogenetic tree of fungi according to MycoCosm portal (adapted from Grigoriev et al., 2014). According to this phylogenetic tree, Pyrenophora teres belongs to the kingdom Fungi, phylum Ascomycota, subphylum Pezizomucotina, and class Dothideomycetes.

Figure 2

Symptoms caused by P. teres on Siberia barley leaves. Control (A), 4 days after infection (B), 7 days after infection (C), and 10 days after infection (D).

Figure 3

The biosynthetic pathway of aspergilomarasmine A (toxin C) and its derivatives (toxin A and toxin B) and their chemical structures (inspired from Friis et al., 1991).

Figure 4

Dynamics of net blotch epidemics adapted from Suffert et al. (2011). Red arrows indicate P. teres wind-dispersed infections and blue arrows indicate splash-dispersed infections. The months with a brown color indicate that the source of inoculum comes from swarming debris on the soil, while the months with a green color indicate a source of inoculum mainly from the aerial parts of the plants. The numbers indicate the pathogen’s infection stages: 1: infection by P. teres ascospores present on infected barley debris; 2: mycelium present on grass species infects barley young plants; 3: the net blotch disease progresses from the bottom to the top of the barley plant; 4: disseminated by the wind, conidia contaminate other barley plants; 5: heavily infected crops show abortion of the ear; and 6: Pyrenophora teres colonizes the senescent tissues and produces perithecia on straw and grass species.

Figure 5

Vegetative and reproductive forms of P. teres and its symptoms on barley leaves. Mycelium of P. teres in barley leaf deposited on PDA medium (A), conidia of P. teres (B), chlorosis and necrosis symptoms on barley leaf caused by P. teres (C), and penetration of mycelium (red arrow) through barley leaf (D).

Figure 6

Assessment on detached leaves. The barley leaves were disinfected in an ethanol bath at 70°C followed by rinsing in three successive sterile water baths. All the leaves were cut to the same length then placed on agar-agar medium. These leaves were then wounded with a wooden pick. A volume of 10 μl was deposited at the level of the wound containing sterile water for a control condition (A) or P. teres spores at a concentration of 10⁵ spores.ml⁻¹ for the infected condition (B).

Figure 7

The schematic model of the fungal growth and symptoms’ development in a susceptible barley leaf. Each enzyme occurs at a specific time of infection. At 24 h, the spores germinate and form an appressorium through the plant epidermis supposing a biotrophic stage. By 96 h, P. teres is growing inside the barley leaf and develops chlorosis and necrosis suggesting a necrotroph stage. Colored bars represent the genes expressed during the plant/pathogen interaction and describe their molecular function(s) (Inspired from Ismail and Able, 2017).