Progress 10/01/98 to 09/30/03
Outputs
While investigating the effects of stress (including biological control agents) on the model worm, C. elegans we observed induction of matricidal hatching. This occurred in C. elegans subject to starvation, as when placed in water without food, or to stress, as when exposed to chitinase-producing bacteria or high salt concentrations, wherein adults became filled with juveniles (Fig. 1). Such observations lead us to consider why such behavior occurs, and whether matricidal hatching evolved as a life history phenomenon, and whether the behavior enhances nematode survival and fitness. We determined that in C. elegans, the internal retention of progeny allows juveniles to consume parent body contents, and obtain sufficient nutrition to reach the resistant, long-lived dauer stage. If starved under similarly extreme conditions, larvae from eggs laid outside of the body are unable to develop into dauers. To assess whether the phenomenon was specific to laboratory standard
strain N2 and whether genetic variation plays a role in the phenomenon, four other wild-type strains of C. elegans were subject to starvation. The frequency of bagging was high in all cases. Preliminary results with the related nematode C. briggsae also revealed a relatively high frequency of bagging. We have interpreted this switch from ovipary, or laying eggs, to bearing live young as facultative vivipary. This switch is induced by starvation of late L4s, young adults, or gravid adults. In C. elegans, vivipary is the altruistic allocation of all available parental energy and nutrients to progeny, with the associated costs to adult hermaphrodites of truncated life span and fecundity. These insights may be useful relative to other nematodes and their responses to stress.
Impacts
Because the bacterium Lysobacter enzymogenes strain C3 produces chitinases, lipases, and proteases, it has potential as a biological control agent of plant parasitic nematodes. Survival strategies related to the dauer in C. elegans may yield insights on survival among plant-parasitic or animal-parasitic nematodes.
Publications
- Chen, J. and Caswell-Chen, E. P. 2003. Why Caenorhabditis elegans adults sacrifice their bodies to progeny. Nematology. In press. Chen, J. and Caswell-Chen, E. P. 2003. The ecology of C. elegans: Phenotypic plasticity, survival, and facultative vivipary. Journal of Nematology. 35:329-330. Abstract.. Chen, J. and Caswell-Chen, E. P. 2003. Bagging as a part of the C. elegans life cycle. Program and Abstracts of 14th International C. elegans meeting, page 192. Abstract.
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Progress 01/01/02 to 12/31/02
Outputs
The bacterium Lysobacter enzymogenes strain C3 produces chitinases, lipases, and proteases and so has potential as a biological control agent of plant parasitic nematodes. We assessed the influence of L. enzymogenes strain C3 against the bacterial-feeding nematode Caenorhabditis elegans, and the plant-parasitic nematodes Heterodera schachtii and Meloidogyne javanica. Exposure of C. elegans to commercial chitinase at a rate of 0.21 unit/ml in agar resulted in five times fewer progeny juveniles than without chitinase. Exposure of C. elegans to L. enzymogenes strain C3 on agar plates resulted in almost complete elimination of egg production, and death of 94 percent of hatched juveniles after two days. Hatch of H. schachtii eggs on a lawn of L. enzymogenes on agar was about 50 percent as compared to 80 percent hatch on a lawn of E. coli, and hatched juveniles died as the cuticle and body contents disintegrated. Juveniles of Meloidogyne javanica died after exposure to a
seven-day old broth culture of L. enzymogenes for four days. The death and disintegration of juvenile nematodes suggests activity of proteases and lipases as has been reported for this strain. It is possible that the strain C3 may be a natural parasite of nematodes. Our research led us to further assess how environmental stress influences C. elegans. We found that wild-type and mutant C. elegans respond to starvation and stresses such as antimicrobial agents, high salt concentrations, and antagonistic bacteria by retaining eggs so that progeny hatch internally. Some of the resultant larvae consumed the parent body contents and became long-lived, resistant dauers, even under conditions of complete starvation. During this process, the parent life span was shortened. The internally produced larvae have similar life span and fertility as compared to larvae arising from laid eggs. We also observed that in C. elegans, the internal retention of larvae in response to stress and starvation
allows the larvae to feed on the parent body contents and so obtain sufficient nutrition to reach the resistant, long-lived dauer stage. Our evidence shows that intra-uterine hatch is a part of the C. elegans life cycle, and complements androdioecy and the dauer stage to enhance progeny survival and dispersal under stress. The phenomenon may also provide insights into the evolution of reproduction and longevity. Understanding trade-offs among parental life span, reproduction, and survival of progeny in the model C. elegans may provide insights into survival of plant-parasitic nematodes.
Impacts
Because the bacterium Lysobacter enzymogenes strain C3 produces chitinases, lipases, and proteases, it has potential as a biological control agent of plant parasitic nematodes. It may function in new integrated nematode management tactics to decrease numbers of plant-parasitic nematodes in agricultural soils. Further research on this possible biological control agent will be conducted.
Publications
- Caswell-Chen, E. P. 2002. Progress report 2002 from U.C. Davis, Multi-State Project W-186 Genetic variability in the cyst and root-knot nematodes.
- Chen, J. and Caswell-Chen, E. P. 2002. Dual modes of reproduction in Caenorhabditis elegans. Nematology 4:202-203. Abstract.
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Progress 01/01/01 to 12/31/01
Outputs
A host plant and nematode database called Nemabase has been developed by faculty at the University of California, Davis. The database includes information obtained from the published literature, and as of Dec. 2000 covered the nematology literature up to ca. 1994, and included approximately 24,000 records. NEMABASE can be interrogated directly via the UCD Dept. of Nematology WWW homepage: (http://ucdnema.ucdavis.edu/imagemap/nemmap/ent156html/contents). NEMABASE is also distributed through the University of California Integrated Pest Management (UCIPM) project, and can be downloaded from the UCIPM web site (http://www.ipm.ucdavis.edu). Nemabase has been described previously (Caswell-Chen et al., 1995). A few years year ago, we undertook the development of a knowledge-based system ("KNOWLEDGE") using NEMABASE as a core database. To make the KNOWLEDGE database easier to interpret, we removed all records in NEMABASE that originated from Siddiqui et al. (1973) and from
Goodey et al. (1965) and placed those into separate databases. The Siddiqui database contains 5,137 records while the Goodey database contains 10,138 records, leaving ca. 24,000 records from NEMABASE in KNOWLEDGE. All three databases have been supplied on a CD ROM for the W-186 membership. During 2001 he information in KNOWLEDGE was updated from the published nematology literature, and during 2001 ca 8,000 new records representing data from the nematology literature published since ca. 1994 was entered into the database to bring the records up to date. There are now 32,382 records in KNOWLEDGE.
Impacts
Many clients will use the database to determine the host-range of nematodes, and to plan non-nematicidal nematode management strategies. Use of rotations or resistance to alleviate nematode damage should be significantly enhanced by the availability of this database and so decrease negative environmental impacts of nematicide use, by aiding reduction of nematicide use in agricultural systems.
Publications
- Caswell-Chen, E. P. 2001. Progress report from U.C. Davis, Multi-State Project W-186 Genetic variability in the cyst and root-knot nematodes.
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Progress 01/01/00 to 12/31/00
Outputs
In cooperation with University of Hawaii personnel, genetic variability among Heterodera schachtii isolates from Maui was assessed. Soil samples were collected from six commercial cole-crop fields on Maui that were known to be infested with the sugar-beet cyst nematode (SBCN), H. schachtii. Cysts were extracted from soil by elutriation, and cabbage plant cultures were inoculated with the cysts. Two California isolates of SBCN that have been maintained in the greenhouse at the UC Davis Department of Nematology were also included. Prior to collecting cysts for DNA extraction, all eight of the isolates were maintained on cabbage cv. Copenhagen Market, and were transferred onto new plants every few months. The cysts were extracted from cultures by Cobb sieving, and DNA was extracted from approximately 50 young, fecund cysts. DNA extractions were conducted using DNeasy Tissue Kit (Qiagen, Inc., Valencia, CA). We performed the extractions according to the company's protocol
except for slight modifications. Once DNA extractions were complete, RAPD PCR analysis of the isolates was conducted. Twenty different primers were used (Operon OPA set -Operon Technologies, Alameda, CA). The reactions were analyzed by agarose gel (1.2 percent) electrophoresis after completion. Amplified DNA fragments were resolved using UV light and photographed. Gels were assessed for the presence of markers among isolates, and the data were entered into a binomial presence-absence matrix. For preliminary analyses, the data were subject to nearest neighbor cluster analysis and pairwise Jaccard binary similarity coefficients were determined. Approximately 150 DNA markers were produced by the OPA set of primers. Preliminary analyses, not unexpectedly, revealed considerable genetic variability among the Maui isolates. The southernmost of the Maui isolates, was removed from the other Maui isolates as indicated by cluster analysis, and was the least similar of the Maui isolates. As
expected, the two California SBCN isolates were clustered together, and were more similar to each other than to any of the Maui isolates. The Maui isolates are more similar to each other than to the California isolates. The genetic variability among the Maui isolates might be interpreted in several ways. It is possible that a limited number of colonization events were responsible for the introduction of SBCN to Maui, and that since the introduction of the nematode it has continually been moved among the different locations. The Maui isolate that was the most different was obtained from a location that is somewhat geographically distant from the other Maui locations. A more detailed analysis of other markers is suggested.
Impacts
Alternatives to nematicides are desired components of sustainable, integrated nematode management, and resistant plants are a primary alternative tactic. Resistance to Heterodera schachtii has been cloned, and might be used to engineer resistant plants. It is expected that the results of this research will aid in understanding the potential for resistance-breaking cyst nematodes to be selected from among isolates from Maui.
Publications
- No publications reported this period
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Progress 01/01/99 to 12/31/99
Outputs
Experiments were conducted to assess the influence of sequential inbreeding on isolates of Heterodera schachtii (SBCN). Two California SBCN isolates were used in the experiments. One isolate has been in continuous greenhouse culture at UCD for ca. 9 years, while the other has been in continuous greenhouse culture for approximately 35 years. Single cysts were placed on individual cabbage plants and were maintained in the growth chamber for 30 days, then resulting single cysts were transferred to new seedling cabbages. This process was continued for three generations, at which time the populations crashed. At each generation, when cysts were observed, up to 15 cysts were collected, crushed individually, and the number of eggs per cyst determined. Inbred lines were extremely difficult to maintain from the culture that had been in the greenhouse the longest. For the isolate that had been maintained for a shorter time, several lines were successfully propagated. In two
lines no significant difference was detected in number of eggs per cyst between generations two and three; in one line the number significantly decreased between the generations; and, in three lines the number was significantly increased between the generations. The experiment needs to be repeated. Six isolates of SBCN were collected from different locations in Maui, Hawaii and were cultured on cabbage in the greenhouse. Comparisons of RAPD markers using have revealed differences in genetic markers among the isolates.
Impacts
(N/A)
Publications
- No publications reported this period
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Progress 01/01/98 to 12/01/98
Outputs
The hypothesis that host plants exert selection pressure on HETERODERA SCHACHTII (SBCN) populations was tested. Host selection of genotypes from three genetically distinct SBCN isolates was assessed using cabbage, sugarbeet, oilseed radish (RAPHANUS SATIVUS, or RS) and white mustard (SINAPIS ALBA, or SA). The plants represent a range of susceptibility to SBCN and included RS and SA because cultivars of those species have been used as trap crops for SBCN in Europe. Genotypic differences in AFLP and RAPD markers were detected among the isolates after they reproduced on the different hosts. The poorest host plant (RS) resulted in the greatest number of changes in both AFLP and RAPD markers. Oilseed radish selected nematode genotypes in less than four nematode generations. The nematode population genotypes detected by RAPD analyses after selection on oilseed radish were observed even after nematode populations were transferred back to the other three hosts. The genetic
markers that were detected after selection were influenced by the genotypes of the original nematode isolates. The results indicate the utility of RAPDs and AFLPs for identifying and monitoring intraspecific genetic variability in nematodes and for understanding nematode population responses to host plants. Research to assess the capacity of California isolates of SBCN to parasitize SBCN-resistant sugarbeets was initiated. As, expected a few cysts were found on SBCN-resistant plants, and the nematodes will be further characterized.
Impacts
(N/A)
Publications
- KAPLAN, M., CASWELL-CHEN, E.P., and WILLIAMSON, V. M. 1999. Assessment of host-induced selection on three geographic isolates of HETERODERA SCHACHTII using RAPD AND AFLP markers. Phytopathol.
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Progress 01/01/97 to 12/01/97
Outputs
The effect of weeds on the life cycle of HETERODERA SCHACHTII (Hs) was investigated. SINAPIS ARVENSIS (Sa), RAPHANUS RAPHANISTRUM (Rr), CAPSELLA BURSA-PASTORIS(Cbp), CHENOPODIUM ALBUM (Ca), AMARANTUHS RETROFLEXUS (Ar), SOLANUM NIGRUM (Sn), AND PORTULACA OLERACEA (Po) were compared with BRASSICA OLERACEA (Bo) AND BETA VULGARIS (Bv) (hosts) and MEDICAGO SATIVA (Ms) (nonhost). Egg hatch increased with exposure to Sa root diffusate. Juveniles of Hs penetrated roots of all weeds. More cysts and eggs were recovered from Sa, Rr, and Cbp than other weeds. The ratio of egg production on weeds to egg production on Bv indicated that Sa was a good host, Rr and Cbp were intermediate hosts, and Ca, Ar, Sn, and Po were poor hosts. The ability of four different hosts (white mustard, sugarbeet, cabbage, and oilseed radish) to select specific genotypes among three isolates of Hs was investigated. Nematode phenotypic responses occurred in less than four generations, and included changes
in morphometrics, male-to-female ratios, total number of nematodes, clutch size, and number of eggs. Statistically, changes were influenced both by genetic differences among isolates, and by host. The isolates were differentiated by the ratio of body length-to-body width, and number of males on white mustard. The ratio of males-to-females was greatest on oilseed radish. The number of cysts, males, and eggs, and the clutch size were affected by both isolate and host. Using amplified fragment length polymorphisms (AFLP) and random amplified polymorphic DNA (RAPD) markers, genotypic differences were detected.
Impacts
(N/A)
Publications
- CASWELL-CHEN, E. P., and WESTERDAHL, B. B. 1997. Management of sugarbeet cyst (SBCN) and root-knot nematode (RKN). 1998 Sugarbeet Res. Rev. (Ann. Prog. Rep. to Cal. Beet Growers Assoc., 1996-1997).
- KAPLAN, M. 1997. Influence of four plants of differing host quality on three genetically distinct isolates of HETERODERA SCHACHTII: A morphometric, demographic, and genetic analysis of host-induced selection. Ph.D. thesis. Univ. Calif.
- WESTERDAHL, B. B, CASWELL-CHEN, E. P. and NORRIS, R. F. 1997. Sugarbeet cyst nematode: In-field assessment of damage/economic thresholds on cole crops and reproductive potential on weeds. Ann.
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Progress 01/01/96 to 12/30/96
Outputs
My lab continues to investigate HETERODERA SCHACHTII (SBCN) genetics, damage thresholds, and reproduction and development. Some nematologists think the damage threshold for SBCN on sugarbeets in northern California might be higher than that observed in southern California, because of cooler temperatures in the north. However, microplot and field experiments to define the damage threshold for SBCN (for fall harvest and overwintered beets) on sugarbeets in northern California reveal that the damage threshold is less than 1 egg per cc of soil, as low as that observed in southern California. We are assessing the influence of host plant on different geographic isolates of SBCN. Preliminary data show phenotypic variation among three geographic populations of SBCN, on oilseed radish, white mustard, cabbage, and sugarbeet. Differences are manifested with respect to cyst production, clutch size, male to female ratios, and morphometrics. Selection pressures imposed by the afore
mentioned crops have resulted in changes in aggressiveness on subsequent hosts, and changes in genetic markers. Fewer cysts and eggs per cyst were produced on oilseed radish and white mustard than on cabbage or sugarbeet. Differences were observed among SBCN isolates in the number of cysts produced on the white mustard. There was no difference in the total number of cysts among the three isolates on cabbage. However, there were differences among isolates with respect to the number of eggs per cyst produced.
Impacts
(N/A)
Publications
- KAPLAN, M., and CASWELL-CHEN, E. P. 1996. Differential microevolution of HETERODERA SCHACHTII isolates in response to host selection. Third InternationalCongress of Nematology. Abstr.
- WILLIAMSON, V. M., CASWELL-CHEN, E. P., WESTERDAHL, B.B., WU, F. F., and CARYL, G. 1997. A PCR assay to identify and distinguish single juveniles of MELOIDOGYNEHAPLA and M. CHITWOODI. J Nematol. Accept for Pub.
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Progress 01/01/95 to 12/30/95
Outputs
My lab is investigating HETERODERA SCHACHTII (SBCN) genetics, damage thresholds,and reproduction and development. SBCN numbers may appear to increase without a host. Results from microplot and growth chamber research reveals that white cysts mature to become brown cysts, egg number per cyst increases, and juveniles develop into cysts on root fragments devoid of foliage. SBCN numbers may increase during fallow periods if host root fragments are left in soil. In microplot and field experiments the damage threshold for SBCN (spring plant, fall harvest) on sugarbeets is approximately 1 egg per g of soil or less. We are assessing the influence of host plant on different geographic isolates of SBCN. Thus far it seems that host plant acts as a selection pressure, and that different SBCN isolates are differentially affected by different hosts. Significant differences in clutch size (eggs/cyst) and in body length and width of preinfective second-stage juveniles were detected
among SBCN isolates. Preliminary analysis of random amplified polymorphic DNA (RAPD) revealed differences among nematodes from a single geographic origin after they were cultured on white mustard, oilseed radish, sugarbeet, and cabbage. Molecular markers for identification of root-knot nematodes has been investigated, and primers derived from random amplified polymorphic DNA (RAPD) that distinguish MELOIDOGYNE HAPLA and M. CHITWOODI from each other and from other root-knot nematode species have been identified.
Impacts
(N/A)
Publications
- GARDNER, J., and CASWELL-CHEN, E. P. 1996. Influence of cyst maturation on apparent population increases by HETERODERA SCHACHTII on root remnants. Fund Appl Nematol. Accept for pub.
- GARDNER, J. 1995. Influence of cyst maturation on apparent population increases by HETERODERA SCHACHTII on root remnants. M.S. Thesis. Univ. California, Davis.
- WILLIAMSON, V. M., CASWELL-CHEN, E. P., HANSON, D., and WU, F. F. 1994. PCR for nematode identification. IN: LAMBERTI, F., DEGEORGI, C., and MCK. BIRD, D. (eds.), Advances in Molecular Plant Nematology. pp. 119-128. Plenum Pub Corp: New Y.
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