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| Objective 1 | Objective 2 | Objective 3 |
OBJECTIVES:
Identify and characterize new sources of resistance genes in cotton, selected vegetables, peanut and soybean to plant-parasitic nematodes.
Facilitate the development of nematode resistant cultivars in these crops.
Integrate resistant cultivars and other biotactics into sustainable cropping systems, ensuring the durability of the resistance.
PROCEDURES:
As has been done successfully so far in S-253, a research coordinator per objective will be named to coordinate and report results for each objective in the Revised Project. Additionally, a leader for each cooperative procedure will coordinate the completion and reporting of results to the objective coordinator. Objective and procedure coordinators may meet or otherwise collaborate to further organize research or presentation of data. The efforts of the participating states and the objectives undertaken by those states are listed in Attachments A & B. All states and organizations will perform the appropriate procedures for the phases of the objectives undertaken.
The Revised Regional Project proposal is structured to 1) promote the development of resistance in cotton and certain vegetables important in the southern region of the U. S., 2) enhance the levels of resistance in soybean and peanut, 3) use molecular techniques for resistance development and enhancement, especially in cotton and selected vegetables, and 4) promote the durability of deployed resistance by incorporating other management tools into sustainable agricultural systems. The proposed revision differs from the current S-253 in three major aspects: the in-depth, extended use of molecular genetics for resistance development and nematode monitoring, the increased use of biological and cultural controls to extend the durability of deployed resistance genes, and the emphasis given to cotton and selected vegetables as targets for development of resistance to nematodes. Developing resistant cultivars is a continuing project, and 10 years may be required before new cultivars emerge at the grower level. Because cultivar development remains our highest priority, we will continue this emphasis in the revised project.
Each investigator will compile and analyze his data using procedures appropriate for the experimental design and data will be shared at the annual meeting. The Procedure Coordinator will summarize results under the appropriate crop/procedure. The Objective Coordinator will compile data and summarize results under each objective and forward it to the Chairman for inclusion in the Annual Report. In addition, a Worldwide Web site will be established at the University of Tennessee, Knoxville and hyperlinked to other Plant Pathology and Nematology web sites. The following information will be posted on the web site: Annual Report, Minutes, and a list of crop genotypes with high levels of nematode resistance.
Each station will work on selected portions of the overall project and then share the results. There may be a combined effort on a particular objective in which participating agencies employ different approaches to achieve the same objective. For example, the effort to develop resistant cultivars to Meloidogyne arenaria in peanut will involve using different approaches in several cooperating states. In fact, different breeding strategies are being used in this effort that will avoid duplication but provide complementary information. The protocols for screening for resistance are slightly different for the three crops because 1) there are inherent differences in the crops; 2) different nematode species require different protocols; and 3) there are differences in facilities in each state. Nevertheless, the end result for each strategy will be the same - identification of resistant genotypes. Inclusion of standard susceptible and resistant cultivars in each test will help normalize variations in test conditions. The number of replications varies with the level of screening – first round, one or two replications; later rounds four or five replications. At each annual meeting further collaborations can be established based on the specific objective for the coming year. Considering it takes 10 years to develop a resistant cultivar, it is difficult to predict how many new cultivars will be developed, but one or two could be expected during the life of this project. Cultivar development is a continuous process and it is likely that cultivars developed during this project are already in the breeding program.
As genotypes of advanced breeding lines with high levels of resistance are identified in each crop, they will be tested by various members of the project with different nematode isolates. This will provide information on how effective the resistance will be throughout the southern region of the United States. A common database comprised of the reactions of new tolerant and resistant lines and genotypes to various nematode isolates and species will be published on the web site. This data will be updated as new results are available.
All new breeding lines developed by the plant breeder at a particular location will be evaluated for resistance to the appropriate nematode species and/or race. The number of breeding lines may vary by year, location, and changing priorities of the breeder. Regional testing of advanced breeding lines will be done at locations where there is nematological expertise on a particular nematode-crop combination. Although exact numbers of germplasm lines tested in a particular year cannot be predicted, the following crop/nematode combinations were evaluated for resistance during 1996: Soybean - M. arenaria, 122; M. incognita, 101; M. javanica, 101; Heterodera glycines, 278; Hoplolaimus columbus, 67; M. trifoliophila, 20; Rotylenchulus reniformis, 143; Vetch - M. arenaria, 3; M. incognita, 3; Sweet potato - M. incognita, 55; Clover- M. trifoliophila, 35; Peanut - M. arenaria, 34; cotton - M. incognita, 3; Rotylenchulus reniformis, 2.
Project participants will publish and otherwise distribute the results of all PI and germplasm screening trials for resistance to Meloidogyne spp. and Rotylenchulus reniformis in publications easily accessible to plant breeders and researchers worldwide. It is proposed that these publications should include lines considered resistant OR susceptible to avoid future duplication of effort in screening.
Objective 1: Identify and characterize new sources of resistance genes in cotton, selected vegetables, peanut and soybean to plant-parasitic nematodes. Objective Coordinator: R. D. Riggs, AR.
Cotton: Standardized procedures, developed by members of the current project, will be used to evaluate advanced germplasm and cultivars bred for resistance to M. incognita and R. reniformis populations in greenhouse tests (AR, MS, NC, TX). Any transgenic nematode-resistant cotton developed at North Carolina State University will be included in greenhouse as well as field tests. Specific root-knot nematode populations, including race 3 from North Carolina and New Mexico, an aggressive race 4 from North Carolina and a unique population from North Carolina cotton (DNA differs from M. incognita) will be evaluated on cotton lines in greenhouse and microplots. Cotton genotypes M-315 and Deltapine 90 will be provided (TX) as the standard M. incognita-resistant and -susceptible genotypes, respectively, in the cooperating states. A North Carolina and a Georgia population of reniform nematode will be used to screen cotton genotypes in greenhouse tests. Seedlings will be inoculated with 10,000 eggs and juveniles, and will be evaluated for nematode resistance 10 weeks later (MS, NC). If nematode population variance is confirmed, inter-related testing among the states of the above nematode species will be conducted against different levels and sources of resistance.
New cotton lines and wild Gossypium species provided by the cotton breeders will be tested for resistance to Meloidogyne incognita and Rotylenchulus reniformis (AR). If resistance to either nematode is found in any of the new lines or wild species collections, the cotton breeders will attempt to transfer it to Gossypium hirsutum cultivars that are suitable for use in the southern region. A gall rating (0-5, where 0 = no galling and 5 = >100 galls) of 0 or 1 will be considered resistant, 2 or 3 moderately resistant, and > 3 susceptible. Susceptibility to R. reniformis will be based on the numbers of vermiform stages, females, and eggs on designated susceptible and resistant checks. Variation in host reaction among geographical isolates of the nematode species and races will be assessed, and the effect on cultivar development will be ascertained (SC, LA, NC, AR, TX). Western Regional Project W-186 objectives on nematode variability will be interfaced with these objectives where feasible. Standardized procedures, including standard resistant and susceptible checks, will be adopted by the participating states. Benchmark: Identification of cotton genotypes resistant to M. incognita and R. reniformis,1997-2000. (Procedure Coordinator: G. W. Lawrence, MS).
Vegetables: Sweetpotato. Reniform nematode (Rotylenchulus reniformis) is becoming a major pest in many sweetpotato growing areas of Louisiana and Mississippi. Resistance to reniform nematode has not yet been identified in sweetpotato. Accessions from the USDA Ipomoea batatas Plant Introduction collection will be evaluated for resistance to reniform nematode in replicated greenhouse tests (ARS-SC). Single vine cuttings will be inoculated with 2,000 juvenile and adult R. reniformis or 1,000 eggs of M. incognita. Nematode population densities in the soil and eggs on the roots will be quantified 70 days later. The sweetpotato cultivars Jewel, Gold Rush, and Beauregard will be included as standard checks in each test. Pepper. High resistances to root-knot nematodes have been identified in pimento and cayenne peppers (Capsicum annuum). New sources of pepper germplasm (C. annuum and C. chinense) as well as breeding lines of pepper (ARS-SC) and southernpea (AR, ARS-SC) will be evaluated for resistance to various Meloidogyne spp. Pepper seedlings will be inoculated with 3,000 M. incognita eggs and severity of galling and numbers of eggs per gram root will be determined 10 weeks later. Benchmark: Advanced lines of sweetpotato with root-knot resistance, 1998-2002. Procedure coordinator: J. Thies, ARS-SC.
Peanut: Efforts will be made (GA, NC, TX) to characterize different genes for resistance to M. arenaria through continuing independent and complementary research programs. Efforts in Georgia will emphasize further characterization of A. hypogaea germplasm resources in an attempt to identify useful sources of resistance, whereas efforts in North Carolina and Texas will place emphasis on the characterization of genes for resistance recently introgressed into A. hypogaea from wild Arachis species. The interspecific hybrids TxAG-6 and TxAG-7, which are compatible with A. hypogaea, contain multiple genes for resistance obtained from A. batizocoi, A. cardenasii, and A. diogoii. Efforts in Texas will focus on identification of additional genes for resistance to M. arenaria, M. javanica, and the previously undescribed Meloidogyne population (TX). Identification of the resistance genes will be followed by efforts to identify DNA markers linked to each gene. Different approaches for characterization of resistance genes will be used (NC, TX). The mechanism of resistance conditioned by each gene will be characterized by the separate programs. Overall, the objectives are to identify and characterize a battery of resistance genes such that the gene deployment systems can be developed that will enhance the durability of the resistance. Initial identification of resistance will be based on greenhouse tests, with resistance being based on inhibition of nematode reproduction. Mechanism of resistance studies will focus on effects of resistance genes on root penetration, rates of nematode development, and host cell responses to nematode infection. Benchmark: Characterization of resistance genes in peanut, 1997-2000. Procedure coordinator: J. L. Starr, TX.
Soybean: Selected portions of the Northern and Southern Soybean Germplasm Collections, perennial and wild Glycines spp. collections, and advanced breeding lines will continue to be evaluated for resistance to major plant-parasitic nematodes using standardized procedures (AR, GA, KY, MS, NC, ARS-NC, SC, VA). Resistance will be evaluated, using standard resistant and susceptible controls, against multiple species and races of nematodes including H. glycines races 1-4, M. incognita races 3 and 4, M. arenaria races 1 and 2, M. javanica, M. hapla, and R. reniformis. Field tests will be conducted against specific races of H. glycines in which the final nematode population level will be divided by the initial population level to get a reproduction index (AR). Recently introduced germplasm from China consisting of approximately 1,000 lines will be evaluated in the greenhouse against H. glycines races 3 and 4 (ARS-IL). Lines that express resistance will be evaluated against H. glycines races 1-3, 5, 6, and 14. Promising material will be used to develop resistant germplasm adapted for production in the United States. The entire Glycines soja germplasm collection consisting of approximately 800 lines also will be evaluated for resistance to H. glycines races 3 and 4 (ARS-IL).
Mechanisms of resistance to several species of nematodes in genotypes of crop germplasm used in breeding programs for the southern region of the U. S. will be investigated at the tissue, cellular, and molecular levels (NC, GA), e.g. nematode development, hypersensitive reaction, and novel proteins. Understanding the effects of selected resistance genes on the nematode life cycle provides information as to the utility and durability of the resistance in a particular cultivar. Molecular mechanisms of parasitism by H. glycines are under investigation as targets for novel, bioengineered host resistance (NC). Benchmark: Identification of soybean genotypes resistant to Meloidogyne spp., Rotylenchulus reniformis, and Heterodera glycines. Procedure coordinator: E. L. Davis, NC.
Objective 2: Facilitate the development of nematode-resistant cultivars in these crops. Objective coordinator: R. S. Hussey, GA.
Cotton:
In some regions, more than 50% of the fields planted to cotton are infested with southern root-knot nematodes, M. incognita. Nematicides, and to a lesser extent, rotations with crops having root-knot nematode resistance (i. e., soybean), are currently used to manage M. incognita in cotton. Only a few commercial cotton cultivars are available with resistance to M. incognita. Resistance to this nematode species has been identified in a few cotton breeding lines and this resistance will be introgressed into adapted cotton cultivars (AR, TX). Three cotton lines derived from M-240 and M-725 with improved resistance to M. incognita were released in 1996 (TX), and these will be evaluated in the field for resistance and agronomic characteristics (MS, TX). Other new cotton genotypes will be evaluated in the field for resistance to populations of M. incognita obtained from within and among cooperating states in the revised project (SC,TX). Damage threshold values will be established for this resistance in different cotton cultivars with different sources and levels of resistance (AR, SC,TX). The level of nematode resistance and its effect on M. incognita populations and yield of subsequent crops also will be evaluated. Some M. incognita populations are virulent on resistant cotton genotypes. Knowledge of the frequency distribution of these variants from various states will be determined (SC,TX) as the first step in development of resistance gene management systems designed to enhance the durability of these resistance genes.
Selected root-knot nematode- and reniform nematode-resistant cotton lines/cultivars will be planted to evaluate their resistance more precisely (LA, NC). These plants will be exposed to a range of each of the nematodes, and yield and nematode (and disease) reactions will be determined. In addition, more precise damage thresholds and functions (regressions) will be developed. Additional cotton germplasm and breeding lines will be screened in other greenhouse evaluations for suitability as hosts of the reniform nematode (AR, LA, MS). Ultimately, tests for M. incognita and R. reniformis resistance will be conducted in infested fields. Two field sites for each of these two nematodes will be used each year. The most resistant lines/cultivars as well as standard susceptible cultivars will be included. Treatments will be arranged in randomized complete blocks and replicated six times. Cotton growth and nematode populations will be assessed at midseason, and cotton yield, root-gall development (for root-knot), and nematode levels will be determined at harvest (AR, NC). Collected reniform nematode populations will be increased on ‘Rutgers’ tomato in the greenhouse and a number of "pure" cultures will be derived from single egg masses. These populations are needed to confirm trueness-to-type and species confirmation and will be used to assess host range, reproduction, and pathogenicity. Host range studies involve inoculation of host differentials used to separate species and races of root-knot nematode as well as several other leguminous and non-leguminous plant species. Selected populations will be added to sheltered microplots containing cotton cultivar Stoneville LA887. At harvest, plant dry weights, cotton yield, and nematode reproduction will be measured (LA). Benchmark: Contribute to the development of two cultivars with M. incognita-resistance. Procedure Coordinator, E. C. McGawley, LA.
Vegetables: Pathogenicity of populations of reniform nematodes on cucumber, southernpea (cowpea), pepper, and sweetpotato will be assessed in replicated microplot and greenhouse experiments (MS, ARS-SC). Plant yield, dry mass, and nematode reproduction on inoculated and noninoculated plants will be compared. Tomato and certain Cruciferae will be evaluated for resistance to M. incognita, M. hapla and M. trifoliophila (TN). Cucumber. Collaborative research on developing cucumber lines with resistance to M. arenaria, M. incognita races 1-4, and M. javanica will be continued (NC). Southernpea. RAPD techniques will be used to identify markers genetically linked to root-knot nematode resistance in southernpea (ARS-SC). Resistant and susceptible parents and their respective F2 populations will be scored for resistance to M. incognita using standard greenhouse procedures. DNA will be extracted from individual F2 plants, bulked into two pools derived from resistant and susceptible plants, and PCR techniques will be used to screen random primers for markers that co-segregate with the single dominant RK gene. Presence or absence of markers in resistant or susceptible parents, and also in pairs of lines isogenic for the resistance genes, will confirm potential linkages identified in bulked segregant analysis. Sweetpotato. Although sweetpotato cultivars with high resistance to Meloidogyne spp. have been developed, these cultivars do not possess all of the characteristics desired by the U. S. consumer, e. g., skin and flesh color, shape, texture, and flavor. Thus, screening lines for root-knot nematode resistance continues to be a high priority in the development of multiple pest resistant germplasm combined with desirable horticultural characteristics (ARS-SC, MS). All sweetpotato seedlings (potential breeding lines) will routinely be screened for resistance to root-knot nematodes and Fusarium wilt in order to identify and maintain the necessary high resistances in the highly variable hexaploid genome of sweetpotato (ARS-SC). Seedlings will be planted in the greenhouse benches and inoculated with 1,000 eggs of M. incognita and approximately 150,000 conidia of Fusarium oxysporum f. spp. batatas. After 50 days, the root system of each seedling will be examined for the presence of galls and the vascular system will be examined for discoloration caused by the fungus. Those seedlings that are free of galls and vascular discoloration will be selected for further evaluation as potential sweetpotato breeding lines. Cooperative evaluations of advanced sweetpotato breeding lines for resistance to M. incognita and Fusarium wilt will be continued by a nematologist and a plant breeder. Evaluation methods for the advanced sweetpotato breeding lines will be similar to those previously described except that four replicates of five terminal vine cuttings will be planted in sand benches in the greenhouse and inoculated with M. incognita or F. oxysporum f. spp. batatas, ensuring high levels of resistance in the germplasm are maintained (ARS-SC). Advanced sweetpotato breeding lines from NC, ARS-SC, MS, LA will be evaluated for resistances to M. incognita and fusarium wilt in regional tests in the greenhouse (ARS-SC). Beauregard sweetpotato is an exceptionally high yielding sweetpotato cultivar with high resistance to soil pox caused by Streptomyces sp. and is currently the most popular sweetpotato cultivar in the southern U. S. Unfortunately, Beauregard is highly susceptible to root-knot nematodes. Large, unsightly galls develop on the surface of this cultivar in response to infection by root-knot nematodes. Thus, there is an urgent need to develop a Beauregard-type sweetpotato with high resistance to both soil pox and root-knot nematodes. A team consisting of a plant pathologist, plant breeder, and a nematologist will cooperatively evaluate sweetpotato germplasm for resistances to these two diseases (NC). Pepper. The pepper accessions PA-398 (Jamaica Scotch Bonnet), PA-426 (Yellow Scotch Bonnet), and PA-353 (Red Habanero) exhibited high levels of resistance to M. incognita race 3 in evaluations conducted under S-253. Under the new project, PA-398, PA-426, and PA-353 will be evaluated for resistances to M. hapla, M. arenaria and M. javanica (ARS-SC). Benchmark: Contribute to the development of one cultivar of sweetpotato and one pepper cultivar with high resistance to M. incognita. Procedure coordinator: J. Thies, ARS-SC.
Peanut: In continued cooperation with the plant breeders, peanut genotypes will be screened for root-knot nematode resistance (FL, NC, TX). Resistance genes identified previously and under Objective 1 will be introgressed into several peanut cultivars by traditional breeding strategies and through the use of marker assisted breeding using DNA markers linked to the resistance genes. Several markers are currently available that are linked to two and possibly three resistance genes (Burow et al., 1996; Garcia et al., 1996). In the Texas program, seven backcross generations have been achieved with five different recurrent parents (Florunner, NC 7, VC 1, Tamnut 74, and Tamspan 90), representing runner, spanish, and virginia market-type cultivars. Accessions resistant to M. arenaria will be screened in multiple location field tests for yield potential, earliness and other desired agronomic traits (TX). Additionally, efforts will be made to combine nematode resistance with resistance to other important pathogens (i. e., early leafspot and tomato spotted wilt virus), and to obtain peanut genotypes with high ratios of oleic to linoleic fatty acids. Genotypes with high O/L ratios are desired by the peanut processing industry. Marker assisted breeding techniques will allow the development of peanut cultivars with multiple resistance genes, thereby increasing the durability of the resistance. An important aspect will be the introgression of genes for resistance to M. javanica and the newly described Meloidogyne species before these species become more wide spread. Benchmark: Contribute to the development of two peanut cultivars with resistance to Meloidogyne arenaria. Procedure coordinator: J. L. Starr, TX.
Soybean: Breeding lines will be screened for resistance to M. incognita and M. arenaria race 2, in Conetainers® in a greenhouse (Hussey and Boerma, 1981; Luzzi, et al., 1987; Hussey et al., 1991) (GA). Screening with a mixture of isolates should permit the selection of lines with broad resistance that have utility over a wide geographic area. Resistance to cyst, root-knot, and reniform nematodes will be incorporated into soybean cultivars using conventional strategies (AR, ARS-IL, ARS-NC, GA, KY, NC). These efforts include crosses between PI 437654, with general H. glycines resistance and a high level of resistance to R. reniformis, and other high-yielding genotypes with resistance to nematodes as identified under Objective 1. Agronomic performance and nematode resistance will be evaluated in microplot or field experiments, and the most promising lines and progeny will be further tested in appropriate field sites, including uniform variety tests. Even though resistance is the most promising tactic for root-knot nematode management in soybean, virulent biotypes of this nematode may occur and be selected on specific resistant soybean genotypes. A population of M. arenaria (GA-7, Georgia isolate) will be successively cultured on CNS (called R1-CNS isolate) and Jackson (called R1-Jac isolate) under greenhouse conditions to determine whether the ability of race 1 to attack soybean is increased following successive culturing on soybean (GA).
Molecular markers are being derived from RFLP and RAPD analyses of nematode-resistant soybean genotypes for use in marker-assisted selection in breeding programs (GA). The RFLPs associated with resistance to root-knot nematodes in soybean will be used in a marker-assisted soybean breeding program to monitor and incorporate this resistance into superior soybean cultivars grown in the southern U.S. The level of resistance to M. incognita will be increased by using resistance genes in the plant introduction PI 96354, which has a high level of resistance to gall formation and nematode reproduction (GA). Standardized greenhouse screening procedures will be used to screen the F2 progeny for PI 96354-level of resistance to M. incognita, and the presence of the two resistance genes will be confirmed using RFLP markers. Other RFLP markers then will be used to select resistant plants with the greatest percentage of the advanced breeding lines’ genomes (GA).
Developing soybean cultivars with resistance to multiple nematode species is critical for soybean production in the southern U. S. Using standardized procedures, breeding lines will be screened for resistance to different H. glycines races (AR, GA, SC). In the past, some soybean cultivars resistant to the soybean cyst nematode were also resistant to the reniform nematode, R. reniformis. As the economic importance of this nematode increases, resistant cultivars must be available for its management. In a collaborative study, soybean cultivars will be evaluated for resistance to Rotylenchulus reniformis and recommendations will be made for growing these cultivars in the southern U. S. (AR, GA). Similarly, soybean breeding lines and cultivars in Maturity Groups VI, VII, and VIII will be evaluated in fields infested with Hoplolaimus columbus (SC, GA). Benchmark: Contribute to the development of two cultivars with resistance to one or more of the following nematodes: M. incognita, M. arenaria, R. reniformis, and H. glycines. Procedure coordinator: R. S. Hussey, GA.
Objective 3: Integrate resistant cultivars and other biotactics into sustainable cropping systems, ensuring the durability of the resistance. Objective coordinator: D. W. Dickson, FL.
Nematode identification:
New identification strategies for Meloidogyne species useful for resistance studies on all crops, as well as for detailed monitoring of populations occurring in field studies will be employed. The identification of root-knot nematode species is critical in monitoring species shifts and population dynamics of co-inhabiting species and races that occur in rotations and changing agricultural production scenarios. At present, identification of Meloidogyne spp. relies primarily on microscopy to assess their detailed morphology, and to a lesser extent their cytology, host response, and biochemistry. A project has been initiated to utilize the esterase bands that consistently differentiate the major Meloidogyne species to develop species-specific monoclonal antibodies for the practical identification of root-knot nematodes (NC). Genetic probes have been developed for egg masses of M. arenaria and will also be developed for three other major Meloidogyne species (SC) and these probes will be used to identify species in mixed populations. Procedure coordinator: E. L. Davis, NC.
Peanut: Release of root-knot nematode resistant peanut cultivars will be coupled with field and microplot studies on effects of resistance on nematode population dynamics (GA, NC, TX). Damage threshold values for resistant cultivars will be developed from those experiments and compared to those of susceptible cultivars. The data from these experiments will be used in the design of cropping systems alternatives where inclusion of resistant peanut cultivars results in suppression of nematode population densities, or maintenance of low population densities, resulting from other management tactics (AL, TX). Factorial experiments will be established to determine the relative value of plant resistance to nematodes within the group of variables defining specific cropping systems. Appropriate economic analyses will be performed to decide on the value of nematode resistance and relative sustainability of each cropping system. Procedure coordinator: J. L. Starr, TX.
Soybean: The optimal length of rotation between cyst nematode-resistant and susceptible soybean will be determined (AR, KY, NC). The durability of Hartwig-type resistance to H. glycines will continue to be evaluated in ongoing, long-term experiments that integrate soybean cultivars with H. glycines resistance with non-or poor-host crops. The effect of alternating resistant soybean crops with corn in a continuing H. glycines management plan will be determined. Experiments will be established to assess the effectiveness of corn-resistant soybean-corn-susceptible soybean, as well as alternating sources of soybean resistance, in managing H. glycines (KY). Similar experiments are designed to manage R. reniformis and Hoplolaimus columbus (NC). The evaluation of polyspecific soybean nematode communities under different sources of resistance may be assessed if sufficient progress on Objectives 1 and 2 allows (NC, SC). Soybean lines containing resistance from the new sources will be included in three to five-year rotations along with non-hosts and continuous susceptible and resistant cultivars. These studies will provide comparative information on the reduction in H. glycines population levels and the durability of the resistance (AR). In addition, selected soybean cultivars will be assessed for their effects on concomitant population densities of R. reniformis and H. glycines in a field study (GA). At harvest, yield and nematode soil population densities will be determined using standard protocols. Use of resistant cultivars will be integrated with cultural practices and biological control with the fungus ARF18A in field and microplot tests (AR). Fungal antagonists of H. glycines will be investigated in suppressive and conducive soils under various cultural practices (MN). Their potential as biological control agents will be evaluated in vitro and in the field. The ability of potential H. glycines biocontrol fungi to colonize root surfaces will be determined (TN). Field isolates of Fusarium oxysporum and F. solani collected from parasitized eggs will be grown in pure culture, then inoculated onto soybean. The selected isolates will be challenged with H. glycines, and the cycle will be repeated until a highly virulent, root colonizing isolate is selected. Additional research will include testing the effects of rhizosphere, rhizoplane, and H. glycines-inhabiting bacteria as possible biocontrol agents (AR, MN). They will be tested as seed coating formulations and as suspensions added to nonsterile soil infested with H. glycines. Overwintering crops will be evaluated for resistance to Hoplolaimus columbus and M. incognita (SC) and to Heterodera glycines (TN). In Tennessee, wheat or other cyst nematode inhibitory crop will be evaluated for its use as a cover crop on lands subject to substantial erosion. Performance of nematode resistant cultivars and breeding lines of soybean will be evaluated in field sites with infestations of M. arenaria, M. incognita, and H. glycines together with a variety of soilborne pathogenic fungi (AL). The field sites have a number of cropping systems into which soybean cultivars can be included to determine their value in crop production and nematode management. Germplasm having the sources of resistance PI88.788, PI79.772, PI209.332, Cloud or Peking will be rotated in field studies to determine if the durability of resistance has been increased and to determine population dynamics and index of parasitism of H. glycines when different sources of resistance are rotated (ARS-IL). Procedure coordinator: E. C. Bernard, TN.
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