Abstract
Finding beneficial fungi antagonistic toward nematodes is important for developing more sustainable agricultural practices. We isolated abundant fungi from cysts of the beet cyst nematode Heterodera schachtii and tested their interaction with nematodes and sugar beet. By molecular screening of fungal communities colonizing five field populations of H. schachtii using DGGE and Sanger sequencing, three strains identified as Exophiala sp., Pochonia chlamydosporia and Pyrenochaeta sp. were frequently found in infected cysts and then specifically isolated (in pure culture). The three isolates were able to re-infect the cysts and colonize the eggs of H. schachtii in vitro fulfilling Koch’s postulates. In greenhouse trials, the root weight of sugar beet plants grown in substrates inoculated with nematodes and the fungal isolates was significantly higher compared to plants inoculated with nematodes only. The number of cysts propagated on roots was lower in substrates inoculated with Pyrenochaeta sp. than those in substrates inoculated with the other two fungi. However, cyst numbers did not significantly differ from the control because the propagation rate of the nematode increased with the root weight. The proportion of infected eggs per cyst was higher under the fungal treatments than the control, and it increased with the number of propagated cysts. The results showed that the here-studied strains of Exophiala sp., Pochonia chlamydosporia and Pyrenochaeta sp. were frequently found colonizing the nematode cysts of different populations of H. schachtii and were efficient in parasitizing the eggs of the nematode.
Highlights
The beet cyst nematode (BCN) Heterodera schachtii is a cyst-forming plant parasitic nematode causing considerable economic losses in sugar beet (Beta vulgaris) production (Müller 1999)
Cysts of the BCN H. schachtii were collected from soils of five sugar beet fields naturally infected with BCN, located in Lower Saxony and North Rhine-Westphalia in Germany (Table 1)
The ability of Exophiala and Pochonia species to parasitize the eggs of H. schachtii (Chen and Chen 2003; Kerry 2000) could explain the high prevalence of these colonizers inside the cysts originating from different populations in this study
Summary
The beet cyst nematode (BCN) Heterodera schachtii is a cyst-forming plant parasitic nematode causing considerable economic losses in sugar beet (Beta vulgaris) production (Müller 1999). Journal of Pest Science (2021) 94:563–572 of resistant cover crops besides the use of resistant sugar beet cultivars are the most common approaches to manage BCN (Müller 1999). These strategies might be either uneconomic or the resistance efficiency could be lost over time because the parasitism genes of nematodes are highly diverse and plant nematode resistance genes are still elusive (Griffin 1982). Cyst nematode populations can be suppressed by several antagonistic fungi, which are taxonomically diverse and are found throughout the kingdom of fungi This group of fungi is capable of capturing and parasitizing nematodes (Nordbring-Hertz et al 2011). A sub-group of these fungi named as egg parasites attacks the eggs and females of sedentary PPNs including cyst-forming nematodes and infects their host through individual hyphae or specialized infection structures like appressoria (Ashrafi et al 2017; Lopez-Llorca et al 2002; MorganJones et al 1983, 1984)
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