W186: Genetic Variability in the Cyst and Root-Knot Nematodes

(Multistate Research Project)

Status: Inactive/Terminating

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SAES-422 Reports

Annual/Termination Reports:

[09/29/2002] [09/30/2003]

Date of Annual Report: 09/29/2002

Report Information

Annual Meeting Dates: 11/02/2001 - 11/03/2001
Period the Report Covers: 01/01/2001 - 12/01/2001

Participants

Roberts, Philip, University of California;
Caswell-Chen, Edward, University of California Davis;
Sipes, Brent University of Hawaii;
Melakeberhan, Haddish, Michigan State University;
Ingham, Russell, Oregon State University;
Gray, Fred, University of Wyoming;
Cooksey, Donald A., University of California,Administrative Advisor

Brief Summary of Minutes

Minutes Attachment:

Attachment

Accomplishments

Objective 1. Characterize genetic variability as related to resistance, environment, biological processes and morphology. The Rk genes. Cowpea (Vigna unguiculata), tomato (Lycopersicon esculentum and L. peruvianum) and common bean (Phaseolus vulgaris)- root-knot nematode (Meloidogyne spp.) interactions are being used to study genetic variability in nematodes for (a)virulence expression and stability with respect to host resistance genes. Host plant resistance to root-knot nematodes is often the most practical solution for control of these pests in many crops. Resistance is being used both in commercial crop cultivars and in cover crop plantings. However, selection for virulence in nematode populations presents a challenge for crop improvement, with the need to identify and introgress additional genes for resistance and to promote durability of resistance. Analysis is being made of the Rk locus in cowpea that confers resistance to M. incognita and M. javanica. This locus appears to be a complex R gene locus for which we have identified at least four allelic or tandem gene forms. Molecular identification of root-knot nematodes. Meloidogyne partityla was first reported from pecan in the U.S. in 1996, where this root-knot nematode was associated with canopy decline in mature trees. In 2001, populations of Meloidogyne spp. were obtained from the roots of pecan trees from AZ, GA, and NM that exhibited foliar symptoms and root galling consistent with infection by Meloidogyne partityla. Additional samples were also collected from an orchard in TX where the nematode was first reported. By PCR amplification of mtDNA from the nematodes using either the C2FE and 1108 primers (Powers and Harris, 1993, J. Nematol. 25:1-6) or the TRNAH and MRH106 primers (Stanton et al., 1997, Fundam. Appl. Nematol. 20:261-268) in conjunction with published restriction enzyme digestions, it was possible to reliably separate all four M. partityla populations from M. incognita, M. javanica, and M. arenaria which are the other root-knot species previously reported from pecan. We were unable, however, to consistently separate all M. partityla isolates from M. hapla or M. chitwoodi, which are also found in NM but have not been reported from pecan. We are sequencing the amplified mtDNA fragments from M. partityla, M. hapla, and M. chitwoodi to identify a restriction enzyme site that will also allow separation of these species. Variability in Cereal cyst nematode. Cereal cyst nematode, CCN (Heterodera avenae) can cause major yield reductions in cereals such as oats, barley and wheat. The first discovery of CCN from the U.S. was made in western Oregon by Jensen in 1974. It was later determined that growers in this area could manage yield losses by growing fall-planted grains which were much less susceptible to damage that spring cereals. Rotating away from grains also minimized yield loss. Another population was discovered in dryland wheat areas of eastern Oregon by Smiley in the 1980s. Since dryland agriculture has less option for rotation, growers are often forced into a situation of needing to grow wheat after wheat on a regular basis and yields have been reduced by as much as 50%. Yield reductions attributed to CCN have also been reported from southeastern Washington and southeastern Idaho. Variation with species of root-lesion nematodes. In continuation of the previous year, root lesion nematode survey was conducted in potato fields from southwest, south central and southeast Idaho in 2000. A total of 134 samples were collected. Survey revealed that lesion nematodes are one of the predominant economically important nematodes found in all the potato growing regions of Idaho. Pratylenchus spp. has been recorded in potato fields from all the counties. Among all species, P. neglectus is the predominant one found in all the counties. Morphometric studies indicated that no significant differences were observed in the morphology of the specimens collected from different fields in Idaho. DNA analysis of the individual specimens from each species was carried out to confirm the variability exists within and between species. It was found that sample collected from the Lincoln County showed the P. neglectus, which is different from the isolates reported in Idaho. DNA analysis further revealed that this isolate is similar to the isolate collected from a potato field in Canada. Objective 2. Determine nematode fitness and adaptability relative to environment, host plant and host plant resistance. The Chile system. Greenhouse studies were conducted to determine if different traits related to reproduction by M. incognita were influenced by yellow or purple nutsedges compared to chile. Both nutsedge species and chile were grown alone or in combination, inoculated with root-knot nematodes produced on tomato so as to avoid potential variability due to inoculum source, and sampled at 3-4 day intervals for four weeks beginning just prior to the formation of egg masses. Data on the percentage of infected roots, number of eggs per egg mass, and dynamics of egg production were collected. The percentage of roots infected by M. incognita was affected by plant species or combinations, but not the fecundity of individual females or the dynamics of reproduction. The study was repeated, and the second study is being analyzed. The coffee system. Seedlings of coffee inoculated with M. konaensis were severely galled and roots were also moderately to severely necrotic. Seedlings of Coffea canephora selection 6621 exhibited different levels of tolerance to the nematode. C. liberica var dewevrei and C. arabica cv. Apoata germplasm will be screened against the Kona coffee root-knot nematode, a new species of root-knot nematode attacking coffee on Maui, an unidentified species of lesion nematode from Molokai and Oahu, and the burrowing nematode. The potato system. The Columbia root-knot nematode, Meloidogyne chitwoodi is a serious pest of potato in the Pacific Northwest and in the Netherlands. At present, control is achieved primarily by soil fumigation, a costly and environmentally polluting practice. Resistance has been found in several wild species endemic to Mexico and the U. S. This type of resistance is expressed as lower root infestation rates and a barrier to the successful establishment of a feeding site, giant cells, and reproduction. The juveniles remain in a vermiform stage. It appears that localized cell death accompanies the resistance reaction suggesting the functioning of an R-gene. The inheritance and chromosomal location were identified for Solanum bulbocastanum and S. hougasii sources of infection. The upper arm of chromosome 11 is the location in both species, suggesting synteny and possible presence of the primitive B genome, hypothesized for S. bulbocastanum, in the two species. Recent surveys have confirmed that two of 12 plant introduction accessions of S. fendleri tested were 100% resistant to M. chitwoodi race 1. Resistance from S. bulbocastanum has bee introduced via protoplast fusion into the cultivated potato breeding gene pool and a backcrossing program has produced advanced clones with root-root resistance, good horticultural type, acceptable fry color and long tuber shape. Objective 3. Design and develop management strategies for cyst and root-knot nematodes relative to genetic variability. The Chile system. Field management projects were established in 1997 and 1998 to determine if growing nondormant, M. incognita resistant alfalfa, compared to annual crops such as cotton, in rotation with chile will suppress concomitant populations of root?knot nematodes, yellow nutsedge, and purple nutsedge. In 2001 chile was planted where root-knot resistant alfalfa, root-knot susceptible alfalfa, and cotton had been grown since 1997. Alfalfa yield, yellow and purple nutsedge biomass, and nematode populations were also sampled monthly during the third season of the alfalfa planted in 1998. Yellow and purple nutsedge populations were reduced each year of the alfalfa rotation; however, nutsedge populations were higher in the nematode?susceptible alfalfa cultivar ‘Dona Ana‘ planted at a low plant density than in the resistant Magna 8‘ cultivar. Root?knot nematode populations in the soil were below detectable levels in all alfalfa plots throughout the study. The potato system Management of root-knot nematode Screening of 30 cultivars of bean against the Columbia root-knot nematode (Meloidogyne chitwoodi) and Northern root-knot nematode (Meloidogyne hapla) indicated that in the two cultivars Apore and Carioca total nematode population (M. chitwoodi) in the root and the population per g of the root was minimum. Lowest level of total M. hapla population and per g of root was observed in the cultivar Kodiak. Management of stubby-root nematode The experiment was conducted in a commercial Russet Burbank potato field at Rexberg, Idaho for the stubby root nematode management. This experiment indicated that percent infection of corky ringspot incidence ranged from 1.3 to 2.3%. Temik application significantly reduced the nematode infested tubers as compared to control or Thimet application. In another experiment efficacy of Mocap alone or along with Temik on root knot nematode was evaluated in a field planted with the potato cultivar Russet Burbank. There is a significant increases in the Market yield and total yield by the application of Mocap alone or along with Temik as compared to control. Yield increase was more by Mocap + Temik treatment than Mocap alone. Percent of nematode infested tubers reduced to 60.3 and 25.8 by Mocap and Mocap + Temik as compared to control (95%). Host plant and nematode database NEMABASE. 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 are supplied on a CD ROM for the W-186 membership. The need to update the information in KNOWLEDGE was recognized, 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. W-186 members at the annual meeting in Corvallis were provided a CD ROM with the updated database.

Publications

Avendano, F., F. Pierce, O. Schabenberger, and H. Melakeberhan. (2001). Application of geostatistical tools to assess the spatial distribution of Heterodera glycines. Journal of Nematology, 33: in press. Bosland, P. W., Y. Zewdie, and S. H. Thomas. 2001. NuMex Nematador: southern root-knot nematode resistant cayenne. New Mexico Crop Improvement Association Variety Release. July 16, 2001. Caswell-Chen, E. P., H. Ferris, B. B. Westerdahl, and R. L. Sloan. 1995. A PC/MAC -platform database on the host status of crop and weed species to plant-parasitic nematodes. Nematology Newsletter: An official publication of the Society of Nematologists. 41(2): 7-8. Ehlers, J.D., W.C. Matthews, A.E. Hall, and P.A. Roberts. 2002. Breeding and Evaluation of Cowpeas with High Levels of Broad-based Resistance to Root-knot Nematodes. In: Proceedings of the Third World Cowpea Conference, IITA, Ibadan, Nigeria. (In press). Fallon, D.J., H. K. Kaya, and B.S. Sipes. 2001. Effect of native and non-native entomopathogenic nematodes on Meloidogyne javanica in Hawaii. Journal of Nematology (in press). Gray, F. A. and D. W. Koch. 2001. Trap Crops. Pages 852-854. In: Cultural Practices, Encyclopedia of Pest Management. Marcel Decker, Inc., NY, NY. Hafez, S. L. and P. Sundararaj. 2000. Application and placement of nematicides in the management of stubby root nematode and corky ringspot disease of potato. (in press). Hafez, S.L., D. Miller and P. Sundararaj. 2000. Screening of alfalfa cultivars to the lesion nematode Pratylenchus penetrans for commercial release. Nematologia Mediterranea. 28 : 157-162. Hafez, S. L. and P. Sundararaj. 2000. Evaluation of mocap for management of Meloidogyne chitwoodi in Idaho potatoes. Nematropica. 30 : 130. Hafez, S. L. and P. Sundararaj. 2000. Nematode management research in Idaho and its impact on the growers economy. Nematropica. 30 : 130-131. Hafez, S. L. and P. Sundararaj. 2000. Application and placement of nematicides in the management of stubby root nematode and corky ringspot disease of potato. American Journal of potato Research. 77 : 400. Hafez, S.L., Garo Haroutunian and P. Sundararaj. 2000. Biofumigation and bassamid An alternative integrated approach to methyl bromide for vegetable and fruit production in Lebanon. Proceedings of the Annual International Research conference on Methyl Bromide alternatives and emission reductions, at Orlando, Florida, November 6-9, 2000. Hafez, S. L. and P. Sundararaj. 2000. Resistant reaction of alfalfa cultivars to the lesion nematode Pratylenchus penetrans. Journal of Nematology. 32 : 433. Hafez, S. L. and P. Sundararaj. 2000. Evaluation of fosthiazate for management of Meloidogyne chitwoodi in Idaho potatoes. Journal of Nematology. 32 : 433. Hafez, S.L., and P. Sundararaj. 2001. Impact of agronomic and cultural practices of green manure crops for the management of Heterodera schachtii in sugarbeet. International Journal of Nematology. 10 : 177-182. Hafez, S.L. and P. Sundararaj. 2000. Concomitant interaction of Meloidogyne chitwoodi and Pratylenchus neglectus in potato cropping system. Nematologia Mediterranea. 28: 89 92. Hafez, S. L. and P. Sundararaj. 2000. Evaluation of chemical strategies along with cultural practices for the management of Meloidogyne chitwoodi on potato. International Journal of Nematology. 10: 89 93. Hafez, S.L. and P. Sundararaj. 1999. Efficacy of seed crop meals for the management of Columbia root-knot nematode Meloidogyne chitwoodi on tomato under green house conditions. Nematropica. 29 : 171 - 177. Hafez, S. L. 1999. Potato nematode management. Proceedings of the winter commodity schools.121 125. Ingham R.E. 2000. Alternatives to nematicides for nematode management. In: Fresh Perspectives: Proceedings of the 2000 Pacific Northwest Vegetable Association Annual Convention and Trade Show. Pp 113-119. Ingham, R.E. 2000. Nematode management with and without nematicides; Opportunities and challenges. In: Shenk, M. and M. Kogan (eds.) IPM in Oregon: Achievements and future directions. Oregon State University Extension Service Special Report 1020, Corvallis, OR. Pp.89-97 Jennings, J.W., L.J. Held, D.W. Koch and F.A. Gray. 1999. Economics of growing trap crop radish and grazing lambs with a sugar beet and malt barley rotation. University of Wyoming Cooperative Extension Service Bulletin. B-1077. Jin, R., B.S. Sipes, and D. Borthakur. 2001. Reproduction of Heterodera schachtii on Bt-transgenic cabbage. Russian Journal of Nematology: in press. Kaitany, R., H. Melakeberhan, G. W. Bird and G. Safir. (2000). Association of Phytophthora sojae with Heterodera glycines and nutrient stress. Nematropica, 30: 193-199. Koch, D.W., F.S. Gray and J.R. Gill. 1999. Ten steps to sucessful trap crop use in the Big Horn Basin. University of Wyoming Cooperative Extension Service Bulletin. B-1072. Koch, D.W., F.S. Gray and J.M. Krall. 1999. Trap crops: A promising alternative for sugar beet nematode control. University of Wyoming Cooperative Extension Service Bulletin. B-1029R. Melakeberhan, H. (2001). Embracing the emerging precision agriculture technologies-symposium introduction. Journal of Nematology, 33: in press. Melakeberhan, H., A. L. Jones and G.W. Bird. (2001). Soil pH affects nutrition balance of cherry rootstocks. HortScience, 36: 916-917. Melakeberhan, H., A.L. Jones and G.W. Bird. (2000). Effects of soil pH and Pratylenchus penetrans on the pathogenesis of Pseudomonas syringae pv. syringae and Mazzard seedling mortality. Canadian Journal of Plant Pathology, 22: 131-137. Melakeberhan, H., A. L. Jones and G.W. Bird. (2001). Soil pH affects nutrition balance of cherry rootstocks. HortScience, 36: 916-917. Ndeme, A., P. Donald, G. Noel, H. Melakeberhan, G. Tylka, S. Chen, R. Riggs, T. Niblack, D. Herschman, J. Faghihi, A. MacGuidwin, T. Welacky, and T. Anderson (2001). Soybean yield and Heterodera glycines population dynamics in the Midwestern U.S. and Ontario, Canada. Journal of Nematology, 33: in press. Ouedraogo, J.T., B.S. Gowda, M. Jean, T.J. Close, J.D. Ehlers, A.E. Hall, A.G. Gillaspie, P.A. Roberts, A.M. Ismail, G. Bruening, P. Gepts, M.P. Timko and F.J. Belzile. 2002. An improved genetic map for Cowpea (Vigna unguiculata L.) combining AFLP, RFLP, RAPD and biochemical markers and biological resistance traits. Genome 45: 175-188. Petrillo, M.D. 2001. Virulence and fitness of Meloidogyne incognita in response to susceptible and resistant cowpea. Ph.D. Dissertation, University of California, Riverside. Potenza, C., S. H. Thomas, and C. Sengupta-Gopalan. 2001. Genes induced during early response to Meloidogyne incognita in roots of resistant and susceptible alfalfa cultivars. Plant Science 161:289-299. Roberts, P.A. 2002. Concepts and Consequences of Resistance. Pages 23-41 In: Plant Resistance to Parasitic Nematodes (J.L. Starr, R. Cook and J. Bridge, eds.) CAB International: Wallingford, UK. Sipes, B.S. 2001. Spatial pattern of Radopholus similis in the roots and shoots of Anthurium andreanum. Nematropica: in press. Smith, H. J., F. A. Gray, D.W. Koch, J. M. Krall and L.J. Held. 2001. New technologies for integrated management of the sugar beet nematode, Heterodera schachtii. Phytopathology 91: No. 6 Supplement, S143. Smith, H. J., F. A. Gray, D. W. Koch, J. M. Krall and L. J. Held. 2001. Evaluation of resistant radish and mustard trap crop varieties for sugar beet nematode control. Western Society of Crop Science Meeting, Tucson, AZ., June 11-12 (In Press). Thomas, S. H., S. A. Sanderson, and Z. A. Handoo. 2001. First report of Columbia root-knot nematode (Meloidogyne chitwoodi) in potato in New Mexico. Plant Disease 85:924. Thomas, S. H., J. M. Fuchs, and Z. A. Handoo. 2001. First report of Meloidogyne partityla on pecan in New Mexico. Plant Disease 85:1030. Thomas, S. H., J. M. Fuchs, and A. L. Jacobson. 2001. Meloidogyne partityla: an emerging nematode pest of pecan in New Mexico. Phytopathology 91:S144. Thomas, S. H. 2001. The status of nematodes in western pecan orchards: what we know and what we dont. Thirty-fifth Western Pecan Conference Proceedings. March 4-6, 2001. Las Cruces, NM. Pp. 2-5. Thomas, S. H. and T. L. Kirkpatrick. 2001. Root-knot nematodes. Pp. 40-42. In: Compendium of Cotton Diseases, second edition. T. L. Kirkpatrick and C. S. Rothrock, eds., APS Press. St. Paul, MN. Tsang, M. M. C., A. H. Hara and B. S. Sipes. 2001. A hot water drenching system for disinfesting roots and media of potted palms of the burrowing nematodes. Agricultural Engineering :in press. Wang, K.H., B. S. Sipes, and D. P. Schmitt. 2001. Crotalaria as a cover crop for nematode management: a review. Nematropica: accepted August 2001. Wang, K.H., B. S. Sipes, and D. P. Schmitt. 2001. Management of Rotylenchulus reniformis in pineapple, Ananas comosus, by intercycle cover crops. Journal of Nematology 33: accepted July 2001. Wang, K.H., B. S. Sipes, and D. P. Schmitt. 2001. Suppression of Rotylenchulus reniformis by Crotalaria juncea, Brassica napus, and Tagetes erecta. Nematropica: accepted April 2001. Wang, J., P. A. Donald, T. L. Niblack, G. W. Bird, J. Faghihi, J. M. Ferris, D. J. Jardine, C. Grau, P. E. Lipps, A. E. MacGuidwin, H. Melakeberhan, G. R. Noel, P. Pierson, R. M. Riedel, P. R. Sellers, W. C. Stienstra, T. C. Todd, G. L. Tylka, T. Wheeler, D. S. Wysong. (2000). Soybean cyst nematode reproduction in the north central United States. Plant Disease, 84: 77-82.

Impact Statements

A host plant and nematode database called KNOWLEDGE was developed and distributed to W-186 members.
Analysis of the Rk locus in cowpea that confers resistance to M. incognita and M. javanica will facilitate the development of host plant resistance to root-knot nematodes.
Breeding for resistance to cereal cyst nematode will be enhanced by knowledge of the genetic relatedness of CCN from the western U.S. to each other and to populations from other parts of the world.
Advancements in nematicidal control of plant parasitic nematodes were demonstrated.

Date of Annual Report: 09/30/2003

Report Information

Annual Meeting Dates: 11/08/2002 - 11/09/2002
Period the Report Covers: 01/01/2002 - 12/01/2002

Participants

Robert Riggs - University of Arkansas; Edward Caswell-Chen - University of California, Davis; Phil Roberts - University of California, Riverside; Bradley Hyman - University of California, Riverside; Brent Sipes - University of Hawaii; Saad Hafez - University of Idaho; Haddish Malakeberan - Michigan State University; Tom Powers - University of Nebraska; Steve Thomas - New Mexico State University; Ken Barker - North Carolina State University; Russ Ingham - Oregon State University; Pat Donald - USDA-ARS (South Area Crop Genetics and Production Research Unit,TN); Ekaterina Riga - Washington State University; Fred Gray - University of Wyoming; Don Cooksey - Administrative Advisor, University of California, Riverside

Brief Summary of Minutes

Minutes Attachment:

Attachment

Accomplishments

The goal of W-186 is to fulfil the need for alternative, integrated nematode management through the discovery and development of alternatives to chemical-based soil pathogen and nematode control. This regional project was initiated because the membership recognized the increasing importance of characterizing the genetic variation in nematode populations and understanding how that variation influences the success of alternative nematode management strategies. There are three objectives in the current project: Objective 1: Characterize genetic variability as related to plant parasitic nematode responses to resistance, environment, biological processes, and morphology. Objective 2: Determine nematode fitness and adaptability relative to environment, host plant, and host plant resistance. Objective 3: Design and develop management strategies for cyst and root-knot nematodes relative to genetic variability. Diagnostic test development: In Washington molecular tests for identification of races of Meloidogyne chitwoodi are under development. A two-marker identification system for M. chitwoodi species identification has been tested in Nebraska and applied in a large-scale survey of potato production areas. The multi-state survey for Meloidogyne and Globodera species recovered no nematodes of quarantine significance in Texas, Kansas, Nebraska, Colorado, Wyoming, or North Dakota. Results are available at the National Agricultural Pest Information System (http://www.ceris.purdue.edu/napis/). Paratrichodorus carrying virulent virus particles are the focus of additional diagnostic tests in Washington. Evolutionary relationships based on nucleotide variation within the D3 rDNA region were examined among seven California and other Meloidogyne hapla isolates and seven isolates of apopmictic M. arenaria, M. incognita and M. javanica; a 3 bp insertion distinguished automictic M. hapla from the apopmictic isolates. Nematode population dynamics: In New Mexico the interaction between root-knot nematodes (Meloidogyne species) reproducing on purple and yellow nutsedge and those reproducing on chile pepper was examined in a series of field experiments. Results indicate the presence of nutsedge in chile fields negatively affects root-knot reproduction on chile. Preliminary results measuring differential rates of infection suggest inoculum source may play a role in root-knot nematode infectivity. Population dynamics of Meloidogyne chitwoodi with respect to degree-day accumulation were studied in Oregon and Colorado. Subtle differences were observed among data sets from Oregon, Colorado, Washington, and Idaho, although the general patterns remained the same. Results reaffirm the need for well-timed application of nematicides for maximum efficacy. The relationship between soybean cyst nematode populations and soil pH is a component of ongoing research in Michigan as well as cyst management using a municipal sewage compost mixture. Nematode suppression: Successful suppression of root-knot populations was achieved by planting root-knot resistant alfalfa prior to chile in New Mexico. In addition to the suppression of nematodes due to nematode resistance, alfalfa had the added benefit of reducing nutsedge populations that serve as a reservoir host for Meloidogyne. A range of crop rotation sequences for controlling M. chitwoodi is being tested in Oregon. In Wyoming, trap crops for the sugar beet cyst nematode are being developed as a key management strategy. Work with the resistant sugar beet cultivar Nematop was discontinued due to the beets lack of resistance to Beet curly top virus. Germplasm from Nematop is being used in a new effort to breed nematode resistant beets. Multiyear high-resolution sampling was conducted two fields to determine if hot spots of nematode infestation change annually. Sampling indicated consistency across years suggesting spot treatment may be accurately applied in successive years based on a single sampling. In Washington, a new biological nematicide is being tested. Genetic variability and host resistance: Root-knot nematode (Meloidogyne spp.) interactions with resistance in the host crops cowpea, tomato (Lycopersicon esculentum and L. peruvianum) and common bean interactions are being used to analyze genetic variability in nematodes for (a)virulence expression and stability. Resistance is being used both in commercial crop cultivars and in cover crop plantings for control of root-knot in many crops. New resistance sources have been identified that confer unique specificities that match avirulence genes in the nematode. Selection for virulence in nematode populations has been shown to occur both naturally in fields planted with resistant cultivars and also in the laboratory by experimental manipulation. Durability of resistance is dependent upon utilization of multiple sources of resistance in cropping systems. Analysis of the Rk locus in cowpea that confers resistance to M. incognita and M. javanica revealed at least four allelic or tandem gene forms. Each of these R gene forms has a unique level of resistance expression and is effective against different populations of M. incognita and M. javanica. The Rk locus was placed on the improved genetic map for cowpea, and is located at the bottom of linkage group one. A search for markers closely linked to the Rk gene is being made using AFLP analysis with bulked segregants from a recombinant inbred line population. Virulence in M. incognita to gene Rk was shown to be a heritable trait and can be selected from some but not all individual avirulent nematode lines when inoculated onto resistant plants. In common bean, differential interactions between isolates of M. hapla race A for ability to reproduce on bean plants with a dominant resistance gene were used to analyze genetics of virulence to this R gene. Segregation of avirulence in F3 to F5 nematode families derived from crosses between avirulent and virulent M. hapla parent lines indicated a single gene control of this trait, with avirulence dominant to virulence (recessive).

Publications

Ammiraju, J. S. S., J. C. Veremis, X. Huang, P. A. Roberts and I. Kaloshian. 2003. The heat-stable root-knot nematode resistance gene Mi-9 from Lycopersicon peruvianum is localized on the short arm of chromosome 6. Theor. Appl. Genet. 106:478-484. Avendano, F., O. Schabenberger, F.J. Pierce and H. Melakeberhan. (2003). Geostatistical analysis of field spatial distribution patterns of the soybean cyst nematode, Heterodera glycines. Agronomy Journal, 00. In press. Avendano, F., F. J. Pierce, O. Schabenberger, and H. Melakeberhan (2002). The relationship between soil type and soil texture with spatial distribution of Heterodera glycines. Nematology, 4: 250. Boiteux, L.S., I.C. Bach, M.E.N. Fonseca, A.W. Moita, W.C. Matthews, P.A. Roberts, and P.W. Simon. 2003. Evidence for a dosage-dependent response of the Meloidogyne javanica resistance locus in carrot via linkage analysis with codominant flanking markers. Euphytica. (in press). Bosland, P. W., Y Zewdie, and S. H. Thomas. 2003. NuMex Nematador: Southern root-knot nematode resistant cayenne. HortScience 38: in press. Chen, P. and P.A. Roberts. 2003. Virulence in Meloidogyne hapla differentiated by resistance in common bean (Phaseolus vulgaris). Nematology 5:39-47. Chen, P., P. A. Roberts, A. E. Metcalf, and B. C. Hyman. 2003. Nucleotide substitution patterning within the Meloidogyne rDNA D3 region and its evolutionary implications. Journal of Nematology, in press. Ehlers, J.D., W.C. Matthews, A.E. Hall, and P.A. Roberts. 2002. Breeding and Evaluation of Cowpeas with High Levels of Broad-based Resistance to Root-knot Nematodes. Pg. 41-51 In: Proceedings of the Third World Cowpea Conference, IITA, Ibadan, Nigeria. Gray, F.A. 2003. Alfalfa disease management. University of Wyoming, Agricultural Experiment Station Bulletin B-1136, pp 1-40. Gray, F.A. and G.D. Griffin. 2002. Plant parasitic nematodes of alfalfa in the United States. 2002. Proceedings of the 28th North American Alfalfa Improvement Conference, Sacramento, CA. p. 69. Gray, F.A. and D.W. Koch. 2002. Trap Crops. Pp. 852-854 In: Cultural Practices, Encyclopedia of Pest Management. Marcel Dekker, Inc., NY. Gray, F.A., D.W. Koch, H.J. Smith, L.J. Held and J.M. Krall. 2003. Controlling the sugarbeet nematode (Heterodera schachtii) in the U.S.A., p. 251, Proceedings of the 2003 International Congress of Plant Pathology, Christchurch, New Zealand, Feb. 2-7. Hafez, S.L. and P. Sundararaj. 2002. Integrated nematode management options for the sustainable potato production. Proceedings of the University of Idaho Winter Commodity Schools 2002 . 111-116. Hafez, S.L. and P. Sundararaj. 2002. Sugarbeet cyst nematode management options in Idaho. Proceedings of the University of Idaho Winter Commodity Schools 2002. 231-236. Hafez, S. L. and P. Sundararaj. 2002. 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Impact Statements

The characterization and identification of genetic variability in nematodes in response to management alternatives and environment are helping to guide decisions on the use of various control tactics.
For example, decisions on the use of resistant crop varieties, on rotations, cover and trap cropping and soil amendments are being improved by incorporating knowledge of nematode genetics and biology into the decision making process.