| COOPERATING AGENCIES AND PRINCIPAL LEADERS:
Illinois - D.I. Edwards*: Indiana - J.M. Ferris*: Iowa - G.L. TYlka*-, Kansas - T.C. Todd*-, Michigan - G.W. Bird*, H. Melkeberhan-, Minnesota - D.H. MacDonald*: Missouri - T.L. Niblack*: Nebraska - T.O. Powers*, E.D. Kerr; North Dakota - L.J. Francl*: Ohio - R.M. Riedel*; South Dakota - J.D. Smolik*; Wisconsin - A.E. MacGuidwin*; USDA/CSRS -K.P- Barker-, Administrative Advisor - R.A. Moore. PROGRESS OF THE WORK AND PRINCIPAL ACCOMPLISEMENTS:Objective 1: Determine the intraspecific variability of plant parasitic nematodes.Distribution of soybean cyst nematode (SCN), Heterodera glycines, is constantly being monitored throughout the region. No SCN was found in a survey of 40 North Dakota fields. In Ohio, 38 of 88 counties are positive for SCN. Total number of infested counties in Kansas is 10, with Races 1, 3, and 4 identified. Eleven of the 16 possible races of soybean cyst nematode have been found in Missouri. Sixty per cent of the soybean acreage is infested, resulting in an average annual loss valued at $43 million in 1992. In Indiana, 57 out of 92 counties have one or more infested fields. A conservative estimate of the total annual loss from SCN in Indiana approaches $10.6 million. Races 3. 6, 8 and 10 have been identified, with Race 3 predominating.Selected representatives of the 6 biological species of Heterorhabditis were examined to determine the relationship between genetic markers and species boundaries. Previous characterization of these isolates by SDS PAGE of total protein, allozymes and restriction digestion of genomic DNA demonstrated genetic discontinuities among several species, but did not resolve the species as defined by cross-mating studies. PCR amplification and endonuclease digestion of two genetic loci revealed several restriction sites in both of the products that uniquely characterize each of the species. No intraspecific variation was observed by restriction digestion of these amplified products. DNA sequencing of the products revealed a low level (< 1. 0%) of intraspecific variation in H. bacteriophora and much greater distance (approx. 5-40%) among the biological species. These results support the view that considerable genetic differentiation has accompanied speciation in Heterorhabditis. With root-knot nematode, Meloidogyne, a more complex pattern is evident. Nucleotide sequencing of 2 1 clones from amplification products of 2 individual juveniles of M. arenaria identified 6 clones which displayed high levels of intra-individual variation. Collectively, these variants are extremely divergent from each other, as well as from other Meloidogyne species (M. hapla, M. chitwoodi, M. mayaguensis and M. graminicola), and exhibit considerable distance from M. incognita, M.javanica and M. arenaria- Mitochondrial DNA analyses mirror the pattern of divergence seen in the ribosomal ITS region (Nebraska). Since winter survivorship of a nematode population depends
on temperature and moisture conditions experienced prior to freezing temperatures,
M. hapla was used in a model system to determine whether there are differences
in response to the timing and extent of different cold hardening conditions
among diverse populations. Twelve populations (I from Canada and I 1 from
the US representing northern, southern, eastern and western states) were
examined. Survival was higher for nematodes cold hardened at 4' C prior
to freezing, but there were no consistent differences in survivorship among
populations (Wisconsin).
Objective 2: Determine the variability of nematode-host interactions.Experiments were conducted with soybean cultivars PI 437.654, Forrest, Hartwig and Essex to determine responses to inoculation with M. hapla. PI 437.654 was more susceptible than the other soybean varieties and would be expected to suffer yield losses due to infection in the field (Missouri). (susceptible). Yields at this location were significantly affected by tillage, and were significantly higher in notill plots as compared with conventional tillage. Percentage yield reduction of susceptible cultivars compared with resistant cultivars with either PI 88.788 or PI 437.654 as the source of resistance were not affected by planting date.Confirmation that population estimates of SCN from fall
samples can be used to predict spring preplant populations was confirmed
by field and microplot studies in Missouri. Overwinter survival of H. glycines
ranges from 60- 1 00% in northern Missouri and nonhosts (com, wheat, sorghum,
red clover, fallow and oats) cause no substantial difference in survival
or viability. Microplot studies with 4 soybean isolines differing only
in maturity showed that hatching rates of SCN were dependent on Pi and
mostly unaffected by isoline. Infectivity of second-stage juveniles was
affected by month of sampling, but not by isoline. Dormancy is apparently
obligate for H. glycines populations in north Missouri. Although maturity
date of the soybean host plays only a partial role in its induction, the
dormancy-induction signal is probably due to host phenology.
USEFULNESS OF FINDINGS:Plant parasitic nematodes have been referred to as the hidden enemy. The reason for this description is that they are extremely difficult to observe because most of them are small worm-shaped invertebrates found below ground in the root zone of plants. There they attack, and sometimes enter, and feed on cortical and vascular root cells. The above ground symptoms of root damage caused by nematode feeding are not diagnostic. The results from research by nematologists on this committee are used to inform growers in the North Central region about the most economical and environmentally safe methods to manage plant parasitic nematodes thus maintaining or increasing crop yields. In order to design control strategies, we must know what nematode species are present, what plants they infect, and how they cause root damage. With some species there are differences in how populations, or isolates, behave. AU of these issues are addressed for the most important plant parasitic nematodes found in the region.WORK PLANNED FOR NEXT YEAR:Work in the coming year will include, but not necessarily be restricted to the following areas: Evaluation of soybean cyst nematode resistant lines is an ongoing concern because of the need to develop soybean lines with good resistance to SCN combined with superior yield. Techniques are developed and will be tested to deter-mine both intra- and inter-species variability by biochemical assays. Population levels required for damage (injury threshold levels) will be investigated to determine how they are modified by such abiotic factors as soil moisture, temperature and soil type. Winter survival is another factor to be investigated to see whether fall samples can be used to estimate spring, at-planting, population levels. Some of the data reported in this document represent intermediate results from multi-year studies. Therefore, at least some of the research in 1994 will be directed toward continuing or finishing these aspects of the total research program.PUBLICATIONS ISSUED OR MANUSCRIPTS APPROVED DURING THE YEARSmolik, J.D. 1993. Nematode and Oligochaete populations. in J.D. Smolik (ed.) Agronomic, Economic and Ecological Relationships in Altemative (Organic), Conventional, and Reduced-Till Farming Systems. Agricultural Experiment Station Bulletin B718, Brookings, SD.Smolik, J.D., J. Gerwing, D. Rickerl, T. Schumacher, H. Woodard, and L. Wrage. 1993. Nematode and Oligochaete populations. in 1992 Northeast Reserach Station Annual Progress Report. Plant Science Pamphlet 71, South Dakota State University, Brookings. Yen, J.H., and T.L. Niblack. 1993. The effect of soybean
maturity date on dormancy of Heterodera glycines in Missouri. Proceedings
of the Missouri and Kansas Academies of Science:95.
MISSCELLANEOUS REPORTS: MacGuidwin. A. 1993. Alternative control measures for plant parasitic nematodes. Proceedings of Wisconsin's Annual Potato Meetings. UW- Extension publication. MacGuidwin, A.E. 1993. The potato rot nematode or the peanut rot nematode? The Common'Tater volume 45. Niblack, T.L., 1993. Soybean cyst nematode races. Proceedings of the 22nd Soybean Seed Research Conference:34-40. |