Brief Summary of Minutes of Annual Meeting

The scientists participating in the project, along with their students and support staff, and in many cases private collaborators, brought their collective knowledge and experience to address nematodes affecting trade. Activities in the laboratory, greenhouse, and field have demonstrated how growers and producers can minimize the impacts that nematodes have on trade. This years accomplishments are presented under the four project objectives. Objective 1: Characterization of Nematode Genetic and Biological Variation Relevant to Crop Production and Trade The primary focus of the project has been to provide protocols for rapid and accurate identification of nematodes by state and federal inspectors, scientists, and diagnosticians. PCR primers for COI have been designed and modified for root-knot, cyst, and genera of ectoparasitic nematodes. Little genetic variation was detected among geographically diverse Ditylenchus dipsaci populations recovered from garlic in Oregon, Ontario, Canada, and the Republic of Georgia. Whereas agricultural and native isolates of Criconematidae revealed extensive genetic differentiation within traditionally accepted morphospecies. Project scientists are using the ²-tubulin gene in a metagenomic DNA isolated directly from soil to quantitatively measure plant-parasitic nematode infestation levels. In addition to the ²-tubulin gene, a series of Heterodera glycines expressed genes are being evaluated in the laboratory for metagenomic analyses of soil population densities. Surveys are important for knowing what nematodes are present in an area. Knowledge of the distribution of nematodes is important for their management and control. In Tennessee, 82% of samples had plant-parasitic nematodes including: Heterodera glycines (16%), Meloidogyne incognita (4%), Pratylenchus sp. (19%), Helicotylenchus (50%), Tylenchorhynchus sensu lato (11%), Rotylenchulus (3%); Hoplolaimus magnistylus was detected in soybean, corn and cotton fields but at low levels. Our survey efforts have identified a putative M. graminicola and an undetermined Meloidogyne species on purple nutsedge (Cyperus rotundus) in an agricultural setting and on alkali sacaton (Bouteloua trifida) in native vegetation. Globodera ellingtonae has been described from samples collected 4 years ago. G. ellingtonae is morphologically and molecularly distinct from golden potato cyst (G. rostochiensis), pale potato cyst (Globodera pallida), and tobacco cyst (G. tobaccum). Surveys of banana and corn in Thailand and Hawaii identified included Pratylenchus coffea (Thialand), P. brachyurus (Thialand and Hawaii), P. speijeri (Thialand), and an unknown Pratylenchus species (Thialand and Hawaii). Host-plant resistance in cultivars of our food crops is the most economically and ecologically sustainable approach to nematode management. In initial tests, G. ellingtonae did not result in significant yield loss in potato although potato root exudate stimulated egg hatch. Resistance to G. ellingtonae was identified in potato varieties with the G. rostochiensis Ro1 resistance. Many red-skinned potato cultivars (All Red, Durango, Desiree, Pink Pearl, and Colorado Rose) were susceptible to Meloidogyne incognita, however some cultivars (Rote Ersting and Mountain Rose) exhibited some level of resistance to M. incognita. Desiree was moderately tolerant to both M. javanica and M. konaensis, but intolerant to M. incognita. Red Thumb was the most susceptible/intolerant cultivar to M. incognita, and the most resistant/intolerant to both M. javanica and M. konaensis. There are resistance genes which can be exploited in these cultivars. Ren1 confers resistance to Rotylenchulus reniformis in cotton. The cotton lines with Ren1 tested were stunted during early season growth and yielded less than their sister lines null for Ren1 in the nematode-infested field. Nematode populations were reduced in plots where lines with Ren1 were planted. Lines carrying Ren1, however, tended to have greater fiber strength, better uniformity and lower short fiber content. Of 157 soybean varieties tested, only 7 (JTN-4408, REV®55R83, JTN-5110, AgBorn S06-X79464, ARMOR 49-C3, JTN-4307, ARMOR 50-C3) supported the same low level of R. reniformis reproduction as the resistant cultivars Forrest, Hartwig, and Anand. These soybeans have rotation usefulness. Of 97 public varieties and breeding lines, 24 were as good as the resistance found in the cultivar Forrest for R. reniformis. Twenty eight cowpea lines with resistance to M. incognita previously challenged with R. reniformis populations from Hawaii and Alabama did not have resistance to an Arkansas population of R. reniformis populations either. Another approach project scientists are investigating for identification of resistance is gene expression, particularly those genes expressed in nematode feeding sites. Genes from H. glycines have been engineered into Williams 82 soybean and will be used to identify the functionality of genes involved in defense responses. Nematodes are genetically variable and variability can manifest itself in nematode adaptation to specific soil ecosystems. Thus integrating nematode adaptation and variability into site-specific management strategies should provide producers better tactics for control. Populations of Meloidogyne hapla varied in reproduction and virulence on celery, tomato, potato, and carrot cultivars. In all cases, a M. hapla population isolated from a sandy soil was the most pathogenic. The varying degree of host suitability, however, suggests that the severity of the problem will likely vary by cultivar and population of M. hapla. Identifying the reproductive potential of a M. hapla populations is critical to making site-specific management decisions. Objective 2: Determination of Nematode Adaptation Processes to Hosts, Agro-Ecosystems and Environments Nematodes are often found to behave in unexpected ways. A putative M. graminicola recovered from purple nutsedge produced readily-apparent galls on nutsedge roots, unlike the more commonly encountered M. incognita, which rarely induces galling. Egg masses of M. incognita, however, were readily evident on the surface of infected roots, while those of M. graminicola were nearly always smaller and submerged within the root cortex. Nutsedges infected with M. graminicola were only observed in heavier-textured loam and clay loam soils whereas M. incognita was absent. However, M. graminicola populations were well adapted to survival in aloamy sand soil under microplot conditions. In preliminary greenhouse experiments, the putative M. graminicola failed to reproduce on tomato. Deployment of resistance can place strong selection pressure on the nematode population, ultimately resulting in the loss of effective resistance. Our focus is to understand and manage the deployment of resistance for long term utility. Planting H. glycines- susceptible soybean had no detectable selection on virulence phenotype. When the initial H. glycines population was avirulent, PI 88788-derived cultivar selected a population that overcame PI 88788, and the Peking-derived cultivar selected nematode populations that overcame the resistance in Peking. In contrast, the PI 437654-derived cultivar selected nematode populations that increased reproduction on both PI 88788 and Peking sources of resistance. The NIL-R selected a nematode population that overcame PI 88788 and increased reproduction on Peking. When the initial H. glycines population was virulent on PI 88788, both Peking- and PI 437654-derived cultivars increased reproduction on Peking. No selected population overcame the resistance found in PI 437654. In a long term experiment, H. glycines populations had positive correlations with total nematode abundance, total non-H. glycines nematode abundance, free-living nematode abundance, and bacteria-feeding nematode abundance, suggesting that conditions favoring free-living nematodes can also favor H. glycines. Analysis suggests that in addition to direct impacts, tillage and susceptible cultivar may have indirect impacts on increasing H. glycines population densities through favoring free-living nematodes, while crop rotation is likely to have an indirect impact in decreasing H. glycines through decreasing free-living nematodes. In a soybean cultivar rotation following the cultivar Anand, the H. glycines population was lowered and shifted from race 6 to race 5. In this rotation, soybean yields were higher. A new rotation scheme using moderately and highly resistant soybean cultivars is being initiated to determine rotation schemes that maximize producer profit. Objective 3: Development and Assessment of Nematode Management Strategies in Agricultural Production Systems Management of plant-parasitic nematodes can take the form of pesticide applicationsboth chemical and biological, as well as cultural practices. A low rate of the the fumigant 1,3-dichloropropene, 200 ppm, suppressed M. incognita population densities by 96% in treated grapevines compared to nontreated. Grape quality was also improved with higher brix and lower malic acid content in those vines receiving the fumigant. Nematicide seed treatments are being marketed in crops like cotton and soybean. Field tests trended toward higher yields in treated soybean but no effect on H. glycines reproduction. New chemicals for nematode management are being introduced. On sugar beet infected with H. schachti, combinations of Poncho 600 FS, Poncho Beta FS, Votivo, and Movento increased sugar beet yield by 13 to 23% as compared to the untreated control. The application of Admire, Movento, and Sepresto, alone and combined, for Pratylenchus sp. control increased onion yield by 15% to 70 % as compared to the untreated control and generally produced greater yield than in onion plants treated with the old standard Vydate. MCW-2 (fluensulfone) increased onion yield compared to the untreated control. MCW-2 was also effective against M. chitwoodii and Paratrichodorus on potato compared to an untreated control. Application of MCW-2 in combination with Vydate was an effective management practice for nematodes infecting potato nematodes. Nonchemical tools can be used to manage nematodes inside plant tissue. Nematodes infecting plant tissues can be challenging to eliminate which is especially important for quarantine nematodes. Potato tubers infected with M. chitwoodi that were irradiated with either Cobalt 60 or linear accelerator experienced dramatic decreases in survival. Due to increased restrictions on the use of chemical nematicides, alternative nematode management strategies, including biocontrol, must be developed. Bacillus firmus GB-126 and Paecilomyces lilacinus 251 are two such possible organisms. Cotton seeds treated with B. firmus (1.4 x 107 cfu/seed), or an application of P. lilacinus (0.3% v/v of water), and the combination of both reduced the number of females, eggs, and vermiform life stages of R. reniformis and increased populations of free-living nematodes. Field populations of R. reniformis decreased when exposed to both biocontrol agents. Furthermore, cotton stem diameter and free-living nematode numbers increased with both biocontrol agents. Cotton yields in B. firmus GB-126- and P. lilacinus 251-treated plots were similar to those in aldicarb-treated plots. The time required to screen plant accessions for resistance to nematodes like M. incognita can take months and any shortening of the time would be beneficial. However, the use of shoot cuttings in crops like chile pepper has not been effective as a method to evaluate plants for nematode resistance. Site specific nematode management is becoming more feasible each season. The application of nematicides using variable rate technology requires knowledge of the intra-field variability of the nematode population, which depends on the collection of soil samples and analysis of these samples for nematodes in the laboratory. Hence estimating the nematode infestation using remote sensing and machine learning techniques can be both cost and time effective. Soil texture is currently being explored as a basis for the development of economic thresholds for R. reniformis and creating management zones within cotton fields. Populations of R. reniformis were influenced by soil texture and exhibited a general decrease with increasing median soil particle size. Soil texture in combination with other soil properties will become a useful tool for developing management strategies for R. reniformis on cotton. A web service is currently being developed in which the end user can upload ground or sub-orbital hyperspectral reflectances of their fields and see the results of the predictive models in an easy to use interface which is graphically appealing. Objective 4: Implementation of Rapid Information Transfer of Project Results to Stakeholder Our efforts in rapid information transfer have fallen into two primary areasmeeting presentations and web access. Research results are disseminated to different user groups through presentations at their meetings. Our findings have been presented at national meetings attended by producers, scientists, and professionals. We have made presentations to state and federal regulators. We have presented our results at field days and extension meetings. We also disseminate information to smaller groups through facility tours, email, telephone conversations, and tradition hard copy. Information and findings are published on university web sites.