Abstract
Three closely related nematophagous fungi in the genus Hyalorbilia were compared for their ability to parasitize females and eggs of Heterodera schachtii at different developmental stages. DoUCR50, StM, and ARF were originally isolated from Heterodera schachtii, Meloidogyne incognita, and Heterodera glycines, respectively. Phylogenetic analysis and pairwise sequence analysis showed that DoUCR50 and StM are more closely related to each other than they are to ARF. DoUCR50 parasitism suppressed 100% of the J2 hatch from 3-week-old H. schachtii females and 75% of the hatch from 4-week-old females. Eggs within 5-week-old females were resistant to parasitism, and hatch of J2 was unaffected by exposure to DoUCR50. StM and ARF did not reduce the hatch of J2 from H. schachtii females of any age. Eggs removed from females and spread onto water agar cultures of the fungi were mostly resistant to parasitism. DoUCR50 parasitized only 16% of such eggs from 3-week-old females. Extracellular hydrolytic enzyme production by the three fungal strains grown on PDA or parasitized H. schachtii females was evaluated using API ZYM (bioMérieux) test strips. All three fungi produced extracellular hydrolytic enzymes when grown on PDA or H. schachtii females. Trypsin-like protease activity was uniquely detected in DoUCR50 grown on PDA and H. schachtii females, with the highest activity associated with the fungus grown on parasitized females.
Highlights
IntroductionThe ascomycete fungus Hyalorbilia aff. multiguttu lata DoUCR50 (basionym: Dactylella oviparasitica DoUCR50) is a hyperparasite of the sugarbeet cyst nematode, Heterodera schachtii
The ascomycete fungus Hyalorbilia aff. multiguttu lata DoUCR50 is a hyperparasite of the sugarbeet cyst nematode, Heterodera schachtii
A phylogenetic analysis of rRNA genes and the rRNA ITS region showed that all three fungi belong to an assemblage of fungi in the genus Hyalorbilia, which is a member of the class Orbiliomycetes (Fig. 2)
Summary
The ascomycete fungus Hyalorbilia aff. multiguttu lata DoUCR50 (basionym: Dactylella oviparasitica DoUCR50) is a hyperparasite of the sugarbeet cyst nematode, Heterodera schachtii. An electron microscopic study of the ARF infection process on H. glycines females revealed the presence of holes in the cuticle at infection sites, suggesting the involvement of enzymatic degradation This was the first report of direct penetration by a fungal parasite on a cyst nematode host (Kim et al, 1992). ARF18-L was more effective at suppressing H. glycines nematode numbers and infected more eggs, juveniles, and young females than ARF18-C in assays conducted in the soybean rhizosphere (Timper and Riggs, 1998; Timper et al, 1999) These results highlight the importance of rhizosphere assays for the selection of potential biocontrol strains
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