In a new study of the symbiotic connections between fungi causing black scab of potato and nematodes, scientists made an unexpected discovery.
Production of high-yielding and high-quality potato crops (Solanum tuberosum L.) is a complex task that requires consideration of many aspects, including variety, soil parameters, rainfall and agricultural practices.
In addition, soil organisms such as fungal species, insects and bacteria can obviously influence the development of a potato culture depending on their food preferences.
The complexity of the interaction of many species present in the soil and the cultivated crop is still very little studied. A group of scientists from the Swedish University of Agricultural Sciences investigated the temporary interactions between nematodes affecting the root system of potatoes and a pathogenic fungus Rhizoctonia solanicausing rhizoctonia.
The interaction was studied on potato plants grown in pots under controlled conditions. In two similar experiments, different combinations of nematodes and fungal mycelium were added to the pots three times; upon landing, after 14 days and after 28 days.
Nematodes reduced root biomass, and a combination of nematodes and R. solani led to a decrease in tuber yield in both experiments, but the interaction was not synergistic. In contrast, the number of lesions in the form of stem ulcers decreased in the presence of nematodes compared to only R. solani treatments.
Scientists know little about the synergy of pathogenic fungi and parasitic nematodes
Plant parasitic nematodes, accounting for 15% of the total number of described species of nematodes, are present in soils around the world and are common pathogens in agriculture. They have a wide range of hosts, including potatoes, and are mobile throughout their entire life cycle, either in soil (ectoparasites) or in roots (endoparasites).
The contribution of plant parasitic nematodes to crop loss is likely to be underestimated because aboveground symptoms or irregular tubers are rarely noticeable against the background of the total crop.
However, nematodes affecting the root system (endoparasitic free-living nematodes) can reduce tuber yield by 12% or even more if they are followed by secondary infections by fungi and bacteria.
It is believed that parasitic nematodes can also affect the development of diseases caused by other soil pathogens, synergistically enhancing the effects of pathogenic fungi.
For example, nematodes can respond to the exudates of plants affected by the fungus, or the fungus can penetrate plant tissues through wounds caused by feeding nematodes.
Mushroom pathogen R. solani causes stem ulcers, black coating, or deformed tubers, among other symptoms, such as thick, elephant, peel, and cracks.
The fungus can survive on crop residues in the soil or be carried by seeds when it is present on the tubers as sclerotia (black coating).
On Swedish potato fields with soil R. Solani a large presence of nematodes was noted, but close attention to these two factors was not given.
It is generally accepted that the nematode-afflicting roots Pratylenchus Envranrans affects the effect R. solaninegatively affecting the crop.
Other types of nematodes interacting with R. solani, are, including cyst-forming potato nematodes Globodera rostochiensis и Pale Globodera.
The exposure time of the pathogen and nematode to the plant, as well as the stage of development of the host plant are important for the interaction between organisms and the severity of the disease for the host.
The temporal aspects of exposure and susceptibility due to plant development have also not been sufficiently studied, although there are studies that compare the susceptibility of a variety.
In this experiment, it was assumed that a combination of plant-parasitic nematodes and R. Solani will lead to a more severe ulcerative lesion on the stems and stolons, will cause a decrease in the quantity and quality of tubers due to the high incidence of black plaque and other symptoms.
For the experiments, two types of nematode inoculum were used; in experiment 1 - a complete community of nematodes, in which nematodes with root damage predominated, in particular A. erenatus, and in experiment 2 - pure nematode culture P. crenata.
Adding root nematodes and R. solani had some effect on potato plants in almost all treatments.
Two hypotheses were confirmed, as scientists found that a combination of nematodes and R. solani and that the time of inoculation affected the severity of damage by both the fungus and the nematodes.
However, contrary to the hypotheses of synergy, scientists saw that the quality of tubers and fungal damage on the plant did not depend on the presence of nematodes before inoculation with the fungus.
The severity of the ulcer of the stem did not increase in the presence of nematodes. Moreover, the ulcer of the stem was even less severe when the nematodes were added in combination with the fungus.
Nematodes parasitizing on plants reduced the number of stem ulcer lesions instead of making them more severe, and the nematodes also did not affect fungal damage on stolons or tubers as intended.
One possible explanation may be that nematodes activate resistance mechanisms in potato plants in the same way that root nematodes are able to elicit defense mechanisms in tomatoes, scientists suggested.
“It is important to understand and evaluate the degree of relationship between pathogens to fight disease using appropriate management methods. Therefore, to address these issues, additional research is needed. Our main conclusions are that the crop is influenced by the simultaneous occurrence of nematodes that infect the roots, and R. solani, and that the nematodes can interact with the potato plant, which leads to a decrease in the number of stem ulcers. Our results emphasize the importance of analyzing the presence of nematodes in the field in order to be able to create protective strategies for efficient potato production. A crop rotation with a minimum of four years without potatoes and other agricultural practices may be useful to reduce population R. solani in the field, the effect of crops grown during the period without potatoes will also affect root nematodes, ”the scientists summed up their scientific article published on the portal www.mdpi.com.
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