Suppression of the Plant-Parasitic Nematode Heterodera schachtii by the Fungus Dactylella oviparasitica

This study examined the role of the fungi Dactylella oviparasitica and Fusarium oxysporum in the beet-cyst nematode (Heterodera schachtii) suppressiveness exhibited by a southern Californian soil. In prior research, the abundance of D. oviparasitica rRNA genes positively correlated with high levels of suppressiveness, whereas the abundance of F. oxysporum rRNA genes positively correlated with minimal to moderate levels of suppressiveness. In this report, both fungi were added to fumigation-induced nonsuppressive soil, planted with Swiss chard, and infested with H. schachtii juveniles. After two nematode generations, D. oviparasitica strain 50 reduced the population densities of H. schachtii eggs and juveniles to those in the suppressive soil and H. schachtii cysts to levels lower than in the suppressive soil. F. oxysporum did not significantly reduce H. schachtii populations. These results suggest that D. oviparasitica strain 50 plays a major role in the suppression of H. schachtii population development in this southern Californian soil.

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Bacterial rRNA Genes Associated with Soil Suppressiveness against the Plant-Parasitic Nematode Heterodera schachtii

Applied and Environmental Microbiology ◽

10.1128/aem.69.3.1573-1580.2003 ◽

2003 ◽

Vol 69 (3) ◽

pp. 1573-1580 ◽

Cited By ~ 27

Author(s):

Bei Yin ◽

Lea Valinsky ◽

Xuebiao Gao ◽

J. Ole Becker ◽

James Borneman

Keyword(s):

Parasitic Nematode ◽

Plant Parasitic Nematode ◽

Soil Treatment ◽

Heterodera Schachtii ◽

Rrna Genes ◽

Pcr Analysis ◽

High Sequence Identity ◽

Soil Suppressiveness ◽

Suppressive Soil ◽

Plant Parasitic

ABSTRACT The goal of this study was to identify bacteria involved in soil suppressiveness against the plant-parasitic nematode Heterodera schachtii. Since H. schachtii cysts isolated from the suppressive soil can transfer this beneficial property to nonsuppressive soils, analysis of the cyst-associated microorganisms should lead to the identification of the causal organisms. Our experimental approach was to identify bacterial rRNA genes (rDNA) associated with H. schachtii cysts obtained from soil mixtures with various levels of suppressiveness. We hypothesized that we would be able to identify bacteria involved in the suppressiveness by correlating population shifts with differing levels of suppressiveness. Soil treatments containing different amounts of suppressive and fumigation-induced nonsuppressive soils exhibited various levels of suppressiveness after two nematode generations. The 10%-suppressive-soil treatment contained numbers of eggs per gram of soil similar to those of the 100%-suppressive-soil treatment, indicating that the suppressive factor(s) had been transferred. Bacterial rDNA associated with H. schachtii cysts were identified using a culture-independent method termed oligonucleotide fingerprinting of rRNA genes. Bacteria from five major taxonomic groups (Actinobacteria, Cytophaga-Flexibacter-Bacteroides, α-Proteobacteria, β-Proteobacteria, and γ-Proteobacteria) were identified. Three bacterial rDNA groups contained clones that were more prevalent in the highly suppressive soil treatments than in the less suppressive treatments, indicating a potential involvement in the H. schachtii suppressiveness. When these three groups were examined with specific PCR analyses performed on H. schachtii cysts that developed in soils treated with three biocidal compounds, only one bacterial rDNA group with moderate to high sequence identity to rDNA from several Rhizobium species and uncultured α-proteobacterial clones was consistently associated with the highly suppressive treatments. A quantitative PCR analysis confirmed the association of this Rhizobium-like rDNA group with the H. schachtii suppressiveness.

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Soil suppressiveness to Heterodera schachtii under different cropping sequences

Nematology ◽

10.1163/156854101753389167 ◽

2001 ◽

Vol 3 (6) ◽

pp. 551-558 ◽

Cited By ~ 13

Author(s):

Andreas Westphal ◽

J. Ole Becker

Keyword(s):

Sugar Beet ◽

Significant Loss ◽

Cyst Nematode ◽

Heterodera Schachtii ◽

Population Densities ◽

Soil Suppressiveness ◽

Suppressive Soil ◽

Resistant Cultivars ◽

Oilseed Radish ◽

Swiss Chard

AbstractHeterodera schachtii population densities were monitored in a H. schachtii -suppressive soil cropped in screenhouse experiments for two consecutive seasons with wheat, susceptible or resistant cultivars of either sugar beet or oilseed radish, or left fallow. Heterodera schachtii population densities under wheat and the resistant cultivars of sugar beet and oilseed radish did not differ significantly from the fallow treatment. Populations declined under all crops, with a reproductive factor between 0.08 and 0.57. In glasshouse experiments, introduced H. schachtii populations increased greatly on susceptible Swiss chard grown in previously wheat-monocultured soils, suggesting that significant loss of H. schachtii suppressiveness occurred during the monoculture. Following fallow, two H. schachtii-resistant or two H. schachtii-susceptible cultivars, introduced sugar beet cyst nematode populations remained small, suggesting that suppressiveness had been maintained. In a field trial with H. schachtii suppressive soil, cyst nematode population densities remained lower under wheat, resistant sugar beet, resistant radish and susceptible radish than under susceptible sugar beet.

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Population development of both sexes of Heterodera schachtii is diminished in a beet cyst nematode-suppressive soil

Biological Control ◽

10.1016/s1049-9644(02)00061-0 ◽

2002 ◽

Vol 25 (2) ◽

pp. 187-194 ◽

Cited By ~ 4

Author(s):

X Gao ◽

J.O Becker

Keyword(s):

Cyst Nematode ◽

Heterodera Schachtii ◽

Population Development ◽

Suppressive Soil ◽

Beet Cyst Nematode ◽

Nematode Suppressive Soil

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Induction of Beet-Cyst Nematode Suppressiveness by the Fungi Dactylella oviparasitica and Fusarium oxysporum in Field Microplots

Phytopathology ◽

10.1094/phyto-96-0855 ◽

2006 ◽

Vol 96 (8) ◽

pp. 855-859 ◽

Cited By ~ 13

Author(s):

Rabiu Olatinwo ◽

James Borneman ◽

J. Ole Becker

Keyword(s):

Sugar Beet ◽

Fusarium Oxysporum ◽

Cyst Nematode ◽

Heterodera Schachtii ◽

Field Soil ◽

Degree Days ◽

Population Densities ◽

Time Points ◽

Second Stage ◽

Greenhouse Study

The ability of Dactylella oviparasitica and Fusarium oxysporum to suppress Heterodera schachtii numbers was examined in field microplots. Fungi were individually added to fumigated field soil that was seeded with sugar beet. Four weeks later, soils were infested with H. schachtii second-stage juveniles (J2). At two harvests, 11 weeks and 19 weeks (1,469 and 2,547 degree days (base 8°C), respectively) after nematode-infestation, H. schachtii cyst and egg numbers were assessed. At both time points, D. oviparasitica reduced H. schachtii population densities to those in the naturally suppressive soil, even when additional H. schachtii J2 were added to the microplots after the first harvest. Although F. oxy-sporum did not alter H. schachtii population densities after 11 weeks, significant reductions were detected after 19 weeks. The sustainability of the H. schachtii suppressiveness created by single applications of the fungi at the beginning of the microplot trials was further examined in a greenhouse study. Soil collected at the completion of the microplot trials was potted and seeded with sugar beet. Four weeks later, each pot was infested with H. schachtii J2. Approximately 16 weeks (1,389 degree days) after seeding, the D. oviparasitica-amended soil produced greater fresh root weights and considerably smaller nematode population densities than the nonamended control.

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A New Class of Ubiquitin Extension Proteins Secreted by the Dorsal Pharyngeal Gland in Plant Parasitic Cyst Nematodes

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2004.17.8.846 ◽

2004 ◽

Vol 17 (8) ◽

pp. 846-852 ◽

Cited By ~ 63

Author(s):

Tom Tytgat ◽

Bartel Vanholme ◽

Jan De Meutter ◽

Myriam Claeys ◽

Marjolein Couvreur ◽

...

Keyword(s):

Syncytium Formation ◽

Cyst Nematode ◽

Heterodera Schachtii ◽

Regulatory Function ◽

Cyst Nematodes ◽

New Class ◽

Genes Encoding ◽

Pharyngeal Gland ◽

Positively Charged ◽

Plant Parasitic

By performing cDNA AFLP on pre- and early parasitic juveniles, we identified genes encoding a novel type of ubiquitin extension proteins secreted by the dorsal pharyngeal gland in the cyst nematode Heterodera schachtii. The proteins consist of three domains, a signal peptide for secretion, a mono-ubiquitin domain, and a short C-terminal positively charged domain. A gfp-fusion of this protein is targeted to the nucleolus in tobacco BY-2 cells. We hypothesize that the C-terminal peptide might have a regulatory function during syncytium formation in plant roots.

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