Population dynamics and biocontrol efficacy of the nematophagous fungus Hirsutella rhossiliensis as affected by stage of the soybean cyst nematode

Abstract

a b s t r a c tMonitoring the population dynamics of a biocontrol agent in soil is important for understanding, predicting and increasing its efficacy. In this study, the population dynamics and the efficacy of a promising biocontrol agent against nematode, the fungus Hirsutella rhossiliensis, were investigated in greenhouse experiments with quantitative real-time polymerase chain reaction (PCR) and bioassay. To explore the effects of the fungus on nematode inoculum, soil infested with eggs or second-stage juveniles (J2) of Heterodera glycines was used. The results showed that the quantity of H. rhossiliensis DNA based on real-time PCR decreased over time, regardless of eggs or J2 as inoculum. The quantity of H. rhossiliensis DNA [femtogram (fg)/g soil] was highest (3.83 ± 1.96 Â 10 8 fg/g soil) when the fungus was first added to soil and then decreased rapidly to 3.24 ± 1.22 Â 10 7 fg/g in egg-infested soil and 7.34 ± 2.94 Â 10 7 fg/g in J2-infested soil 17 days after planting, and then declined gradually between 17 and 59 days after planting. The data based on the bioassay showed that the percentage of J2 parasitized by H. rhossiliensis decreased throughout the experiment in both egg-and J2-infested soils. H. rhossiliensis controlled H. glycines more effectively in J2-infested soil than in egg-infested soil. At the end of the experiments (59 days after planting), nematode suppression and plant growth promotion in J2-infested soil were 79% and 55%, respectively, which were higher than the 34% and 2% in egg-infested soil. In soil that was not inoculated with the fungus, the number of H. glycines was 10 times higher in J2-infested soil than in egg-infested soil, indicating the greater nematode inoculum potential in soil infested with J2. DNA yield of H. rhossiliensis was statistically higher in J2-infested soil than in egg-infested soil in earlier period (prior to day 31) (p < 0.05), which is consistent with the hypothesis that the numbers of J2 present during and soon after fungal inoculation are critical for maintaining the population density and biocontrol efficiency of the fungus.

Functional response of the fungus Hirsutella rhossiliensis to the nematode, Heterodera glycines

“…We considered predation rate to be a better index for future assessments because it is a more explicit index for researchers to evaluate the effect of fungal predators on the targeted pests and has been widely used in the assessments of Hr or other fungal biological control agents [43,44]. The fitting of field data by the logistic regression was encouraging (Table 3) and indicated the practical potential of this method for fungal biological control agents.…”

Fungal communities associated with Heterodera glycines and their potential in biological control: a current update

“…Hirsutella rhossiliensis and H. minnesotensis are two fungi that have been found to possess promising biocontrol abilities in a greenhouse study (Chen and Liu, 2005). Greenhouse studies of its ability to control SCN numbers were done alongside development of specific PCR based quantification methods for detecting this fungus in soil (Zhang et al, , 2008. Unlike Fusarium or other Nectriaceae discussed earlier, Hirsutella spp.…”

“…Since then, several extracellular serine proteases from nematode parasitic fungi have been purified and in some cases, the genes involved in their synthesis have been cloned ( Yang et al, 2007 ; Tunlid et al, 2017 ). Serine proteases can help degrade nematode cuticle, thereby giving fungi access to the nematode body to derive nutrition ( Zhang et al, 2008 ; Tunlid and Jansson, 1991 ; Tunlid et al, 2017 ). Hirsutella rhossiliensis is well known as an obligate SCN J2 parasite ( Liu and Chen, 2000, 2001 ).…”

Rhizosphere bacterial communities associated with healthy and Heterodera glycines-infected soybean roots

“…Some fungi and bacteria, such as Purpureocillium lilacinus (formerly Paecilomyces lilacinus) [18], Hirsutella rhossiliensis, Hirsutella. minnesotensis [19,20] and Pasteuria sp. [21], have shown to be potential biocontrol agents.…”