Brief Summary of Minutes of Annual Meeting

W4186 Minutes

14-15 November 2019

Riverside, CA

Present: Phil Roberts, Isgouhi Kaloshian, Saad Hafez, Vince Klink, Russ Ingham, Haddish Melakeberhan, Cynthia Gleason, Jacki Beacham, Brent Sipes, Shahid Siddique

Meeting Summary: Group conversation regarding accomplishments of previous year and future plans for project renewal.

Multistate Project W4186

2019 Annual Report

Project/Activity Number:      W4186

Project/Activity Title:            Variability, Adaptation and Management of Nematodes Impacting Crop Production and Trade

Period Covered:                     2019

Date of This Report:              January 13, 2020

Annual Meeting Date(s):       November 14-15, 2019

Participants:

Beacham, Jacqueline (New Mexico State University)

Dandurand, Louise-Mary (University of Idaho)

Gleason, Cynthia (Washington State University)

Hafez, Saad (University of Idaho)

Ingham, Russell (Oregon State University)

Kaloshian, Isgouhi (University of California-Davis)

Klink, Vince (Mississippi State University)

Lawrence, Kathy (Auburn University)

Melakeberhan, Haddish (Michigan State University)

Powers, Tom (University of Nebraska)

Roberts, Phil (University of California-Riverside)

Siddique, Shahid (University of California-Davis)

Sipes, Brent (University of Hawaii)

Thomas, Stephen (New Mexico State University)

Accomplishments and Impacts

Objective 1:   Characterize genetic and biological variation in nematodes relevant to crop production and trade.

Critical to nematode management practices is the rapid and accurate identification of nematodes for regulatory and management purposes. However, this objective is a major challenge. The following activities have been performed regarding objective 1.

Plant-parasitic nematodes, of which 4,100 species have been described, are estimated to cause 100 billion USD in agricultural loss per year. Economic, health, and environmental considerations make natural host plant resistance a preferred strategy for nematode control, but there are limitations to this approach. In many cases, the resistance conferred by resistance genes is partial, and some of the nematodes are able to survive. Similarly, nematode resistance genes are often effective against only one or a few species, whereas plants are exposed to several pathogens in the field. Another concern is the emergence of pathotypes that can overcome resistance. In view of all these limitations, it is important to identify additional biological mechanisms that can be used to develop novel and durable crop resistance against nematodes. Fundamental to achieving this goal is understanding the mechanisms by which plants recognize and defend themselves against nematodes.

The plant cell plasma membrane contains pattern recognition receptors (PRRs) that mediate recognition of evolutionarily conserved molecules from bacteria, oomycetes, or fungi. A plethora of studies have focused on the recognition and activation of PTI responses during various types of plant -pathogen interactions. The goal of the current project is to identify plant receptors that are implicated in nematode perception. To identify those receptors, Arabidopsis thaliana plants were infected with cyst nematodes and changes in gene expression for all membrane-receptors was measured. In this way, we have so far identified 108 membrane-localized receptors whose expression is significantly upregulated during the invasion and induction stages of nematode infection. Knock-out mutants for approximately 50 genes were tested for nematode infection and 5 receptors were identified that are implicated in nematode susceptibility. The mechanism behind the role of receptors in nematode recognition is being investigated. The research plan focuses initially on the model plant A. thaliana and its interaction with cyst nematode and root-knot nematode. However, the knowledge gained will be transferred to crop plants during the subsequent years, particularly to soybean (Glycine max), almond (Prunus dulcis), tomato (Lycopersicon esculentum) and sugar beet (Beta vulgaris).

In collaboration with a Nebraska-based biotechnological company, MatMaCorp (http://www.matmacorp.com/) we have developed a custom test to simultaneously detect and identify four economically important cyst species. In about two hours, we are able to detect and identify Heterodera avenae (cereal cyst), H. glycines (soybean cyst), H. medicaginis (alfalfa cyst), and H. schachtii (sugarbeet cyst) from soil or root samples, and differentiate them from H. trifolii (clover cyst) or other closely-related nematodes. Each of these cyst nematode species have been observed in the western Great Plains states, and potentially can coexist in fields with cropping strategies that include host plants of multiple species. Barley (Hordeum vulgare), for example, a preferred host of the cereal cyst nematode, is often grown in rotation with sugar beet. Many sugar beet fields in the west have populations of sugar beet cyst nematode. The diagnostic test can be conducted on a single juvenile extracted from the soil or community DNA extracted from the nematode population. No DNA extraction is necessary for working with single infective juveniles. The DNA template is added to a lyophilized C-SAND assay that includes sequence-specific fluorescent probes for each of the four species. These reactions are processed and immediately analyzed on a Solas 8 portable device. We are currently conducting validation tests under a range of conditions.

A second project completed and published was the survey of Pratylenchus species of the Great Plains. It was determined that P. neglectus is the most wide-spread species in the region occurring on most crops grown in the Great Plains. The second most frequently recovered was P. scribneri, which is found in most corns fields in the region. Both species co-occurred in approximately 20% of the fields. Pratylenchus alleni, P. penetrans, and P. zeae were observed in very low frequency (<1%) in the surveyed fields.

A third project for which we contributed over 100 nematode datasets, each representing a nematode community analysis, resulted in a multi-investigator paper published in Nature, that estimated the global abundance and biomass of nematodes.

Columbia Root-knot Nematodes (CRKN, Meloidogyne chitwoodi) infect potato (Solanum tuberosum) tubers and cause quality defects consisting of galling of the tuber surface and small brown spots that surround the female and egg mass inside the tuber. There is little tolerance for infection in tubers in domestic markets for fresh or processed potatoes and crops that exceed these tolerances may be devalued or rejected. Furthermore, there is no tolerance for infection in tubers intended for export to countries where CRKN is considered a quarantined pest and even one infested tuber can prevent a shipment from being exported. Several trials were conducted to test new management strategies using nematicides to control tuber damage from CRKN. After harvest, tubers were peeled and examined for CRKN infection. Any tuber with six or more infection sites was considered a cull.

Metam sodium is considered a fumigant nematicide but has a lower vapor pressure than other fumigants and therefore does not move far from points of injection. This leaves areas in the soil that do not get adequately treated allowing nematodes to survive treatment. In this trial metam sodium was shanked-in 16 in. deep at 30 or 40 gallons per acre (gpa) and then the soil was mixed with a spader- tiller (or not) in an attempt to improve coverage. All treatments significantly reduced percentage of culled tubers compared to the control plots (99%) but none were acceptable. There were no differences between rate (30 gpa = 83%, 40 gpa = 76%) or spader (shank only = 84%, shank plus spader = 75%) treatments. Following a spader treatment of metam sodium at 40 gpa with an oxamyl standard program consisting of an in-furrow application at planting (April 19) followed by chemigation applications at emergence (May 15), 1,272 degree-days base 41F (June 12) and every two weeks until September 4 reduced percentage of culled tubers. There was no difference between ReTurn XL (29%) and Vydate C-LV (39%) formulations of oxamyl.

A season-long program of Velum Prime (Fluopyram) in-furrow and at emergence plus in-season applications of Vydate C-LV reduced the percentage of culled tubers by 81% and was as good as beginning the program with Vydate in-furrow. In contrast to results from a similar trial in 2017, replacing two mid-season Vydate applications with Movento (Spirotetramat) did not reduce the level of control.

In a trial testing broadcast preplant incorporated (PPI) applications of Nimitz (Fluensulfone), Velum Prime, and Vydate, Nimitz alone did not reduce the level of nematode-culled tubers and there was no difference between fall (78%) and spring (67%) applications (Untreated = 82%). Nimitz followed by Velum Prime in-furrow reduced the percentage of culled tubers when Nimitz was applied in the fall (56%) or the spring (45%). A standard Vydate program consisting of an in-furrow application at planting (April 19) followed by chemigation applications at emergence (May 15), 1,272 degree-days base 41F (June 12), and every two weeks until September 4 reduced percentage of culled tubers (19%). The best treatment was fall Nimitz followed by Velum Prime in-furrow, plus Vydate at 1,272 degree-days base 41F (June 12), and every two weeks until September 4 (3%). However, this was not significantly different from the standard Vydate program.

Potatoes rank as one of the four most important staple crops on a global scale, and Washington produces a significant portion of the potatoes grown in the USA. Meloidogyne chitwoodi (also known as the Columbia root-knot nematode) is major problem for potato producers in this region. The nematode infects the potatoes and causes defects in the tuber that can significantly diminish the value of the crop. Because there are no commercially available crops with root-knot nematode resistance, we have been working to develop new forms of nematode controls. Treatment of potato roots with the defense elicitor peptide called Pep1 enhanced potato resistance against root-knot nematodes. In addition, we engineered the rhizobacteria Bacillus subtilis to produce and secrete Pep1. The bacterially-produced Pep1 also increased potato resistance against root-knot nematodes. Using various plant hormone mutants, we determined that the enhanced resistance in the plants is at least partially dependent on the defense hormones salicylic acid and jasmonic acid. Our work with the plant defense elicitor showed that the induced plant defenses were effective against different pathotypes of M. chitwoodi, suggesting a conserved resistance mechanism against the different strains of this nematode. The different pathotypes of M. chitwoodi found in the state of Washington have been an on-going issue because all pathotypes infect potatoes, but they differ in their ability to infect other hosts. Of these pathotypes, race 1 and race 2 differ in their ability to infect alfalfa (Medicago sativa). Alfalfa was previously recommended as a rotation crop to control M. chitwoodi. Race 1 cannot reproduce on alfalfa. However, a second race (Race 2) was discovered that can reproduce on alfalfa, diminishing the effectiveness of alfalfa crops as a nematode control tactic. We are using the genetic variability between races to develop markers so that growers can determine which race(s)/pathotypes are in their fields. We have performed transcriptome analyses on two of the most common pathotypes of M. chitwoodi in the state of Washington. The gene expression information was used to design primers that can distinguish race 1 and race 2 by a simple PCR. We are performing additional sequencing projects to develop more markers for four different races/pathotypes.         

Objective 2:  Determine nematode adaptation processes to hosts, agro-ecosystems and environments.

The procedures that have been developed so that nematodes can be measured can suffer from variation in the execution of the procedures among various laboratories and other factors including environmental conditions. This situation can lead to variation in the outcome of nematode measurements. A number of actions have been performed regarding objective 2.

The northern root-knot nematode (NKRN), a problem in the northern hemisphere vegetable cropping systems, continues to be one of the major foci. Currently there are no commercially available resistant cultivars. The NRKN has parasitic variability that seems to be associated with soil types, and it occurs in varying soil health conditions. The agrobiological basis of NRKN parasitic variability remains unknown. The goal of this project is to understand how NRKN parasitic variability relates to the biological and physiochemical conditions in the environment in which it survives. The objective of this study is to establish any correlation between presence or absence of NRKN and soil health conditions, as indicated by nematode community, in different vegetable production regions of Michigan. To test the objective, 15 vegetable fields in three regions within the lower peninsula of Michigan (east, south-west and north-west) were selected. These fields represented muck and mineral soil types. In each of the fields, five 25 m² area were flagged. Within each 25 m², one geo-reference flag was randomly marked on the rows to collect rhizosphere soil and another flag about 30 cm away in between rows to represent bulk soil. As a control, five sampling points were flagged in an adjacent non-agricultural field. Each sample consisted of approximately 1 liter of composite of 10 cores around a flag. Nematodes were extracted from 100 cc sub-sample of each sample and identified to trophic and colonizer-persister groups to determine soil food web structure and function. The presence or absence of NRKN was tested by planting two weeks-old tomato seedlings cv Rutgers into 300 cc sub-sample from each of the bulk soil samples. The assumption was that the soil from 1 m² will have the same NRKN population. The experiment was set up in a greenhouse set at 8 h dark and 16 h day diurnal cycle. Twelve weeks later, seedlings were assessed for presence or absence of NRKN by gall index. Based on the Ferris et al soil food web model, the rhizosphere and bulk soil in the muck soils were primarily disturbed and the mineral soils primarily degraded. Those of the non-agricultural soils of both soil types were disturbed. In three of the nine mineral soil fields and in all of the muck soils NRKN was present. How the presence of NRKN in degraded and disturbed soil health condition relates to parasitic variability is being investigated.

Analysis of root-knot nematode resistance traits in carrot (Daucus carota) and cowpea (Vigna unguiculata) was conducted to determine presence of novel resistance genes and variation within and between root-knot nematode species for virulence to the resistance traits. In carrot, selections of entries were made from screenings of the USDA carrot germplasm collection exhibiting resistance to Meloidogyne incognita, M. javanica, and M. hapla.  High resistance was found in lines from Brasilia, South Africa and India to M. incognita and M. javanica. In the Brasilia source, QTL mapping using genotyping-by-sequencing derived SNPs revealed resistance determinant loci on carrot chromosomes 4 and 6. These results are being validated through analysis of additional segregating populations. Resistance to M. hapla in a carrot entry from Syria was found effective against nine out of ten different M. hapla isolates collected from different cropping systems and agro-ecologies. Segregation for resistance in a population developed from a heterozygous single root selection conformed to recessive inheritance behavior, and QTL mapping using genotyping-by-sequencing derived SNPs revealed a large-effect QTL on carrot chromosome 9. This result is being confirmed with a second mapping population.

In cowpea, further analysis of the genome-level organization of root-knot nematode resistance traits revealed trait determinants on four of the 11 cowpea chromosomes. Single resistance traits were found for resistance to M. javanica and or M. incognita on chromosomes 1, 3 and 11. However, a complex resistance locus with allelic or tandem duplicated resistance specificities to virulent and avirulent M. incognita and M. javanica isolates, including one gene for resistance to root-galling, was found on cowpea chromosome 4. Fine mapping and candidate gene functional analysis using Agrobacterium rhizogenes-transformed hairy root cowpea plants is in progress to identify the specific coding genes underlying the resistance loci.

Objective 3:  Develop and assess nematode management strategies in agricultural production systems. 

Plant-parasitic nematode the management can proceed down several paths. These paths include host plant resistance, chemical and biological controls with some strategies employing multiple approaches. A number of studies presented below have been performed to address objective 3.

Included in such management plans is been a vineyard nematicide trial that has been performed due to the important agronomics of wine production. Wine distribution, sales, and consumption in New Mexico generates ~$876.7 million in annual economic activity. In 2017, the industry generated ~$51.6 million in state and local taxes, and $55.4 million in federal taxes. Nematodes can cause premature vineyard decline, reduced vine vigor, and increased fungal infection and virus transmission with yield losses of >60% due to nematodes (Teliz et al., 2007).

Recent developments of new nematicides necessitate investigations into these new chemistries their integration with New Mexico cultural practices. A field study was conducted in 2018 to measure Meloidogyne incognita management and wine-grape plant response to three spring application rates (3.5, 5 and 7 pint per acre [pt/acre]) of fluensulfone (Nimitz^®) compared to spirotetramat (Movento^®) and an untreated control.  Treatments were applied to established (~ 20 years) non-grafted Cabernet Sauvignon grape (Vitis vinifera) vines with a history of severe root-knot nematode (M. incognita, RKN) injury under buried drip irrigation. Vines in some areas showed noticeable stunting and berry yield in the block being investigated was < 50% of that achieved prior to root-knot nematode symptom development. A number of observations have been made from the experiments including: (1) No phytotoxicity was observed from any of the three rates of Nimitz or from Movento 21 days after application; (2) Both the 3.5 and 7.0 pt/acre rates of Nimitz showed significant increases in general vine canopy vigor 21 days post-treatment; (3) Soil populations of RKN six weeks after spring treatments were significantly lower with 7.0 pt/acre Nimitz compared to the untreated control; (4) Six weeks after treatment applications, soil root-knot populations were significantly higher in plots treated with 5.0 pt/acre Nimitz compared to the 3.5 and 7.0 pt/acre rates and the untreated control.  This result is puzzling and unexplainable.  The trend persisted in population levels at harvest; (4) No significant reduction in root-knot nematodes occurred following fall application of 3.5 pt/A Nimitz to plots that received the same treatment in spring.  However, there was a large and significant increase in soil RKN numbers in plots previously treated with Movento; (5) Machine-harvested yields tended to be greater in plots treated with Nimitz and less in those treated with Movento compared to untreated plots; (6) Juice quality parameters were largely unaffected by any nematicide treatments in 2018.

Work is being done to start tracking juice quality parameters to evaluate if there is a correlation between juice quality and RKN stress. The Movento treated plots had the highest RKN populations at the end of the season, the lowest yields, the highest juice sugar content, and decreased juice nitrogen values compared to those of other treatments. A pilot project was initiated in 2019 to focus on further evaluating this correlation. Data is currently being analyzed.

A turfgrass nematicide trial is being conducted to evaluate the effects of several commercially available and experimental products on root-knot (Meloidogyne spp.) and ring (Mesocriconema nebraskense) soil nematode counts, visual turf quality, percent green cover, Dark Green Color Index (DGCI), Normalized Differences Vegetation Index (NDVI) and root development before and after treatment applications on Princess 77 bermudagrass (Cynodon dactylon) turf. We have finished the second year of the study and are currently analyzing data to summarize combined findings across both years. The experiments have been arranged as a randomized complete block design (RCBD) with six blocks. The treatments in this experiment include: (1) Non Treated Control; (2) Divanem (Abamectin) 0.28 oz/1,000ft² (4 applications); (3) Nimitz Pro G (Fluensulfone) 1.38 oz/1,000ft² (4 applications); (4) Indemnify (Fluopyram) 0. 3227 oz/1,000ft² (2 applications); (5) Indemnify (Fluopyram) 0. 1963 oz/1,000ft² (2 applications); (6) Indemnify (Fluopyram) 0.3227 oz/1,000ft² (3 applications); (7) Todal (Abamectin) 1.31 oz/1,000ft² (3 applications). Preliminary results from 2018 indicate that both high rate treatments of Indemnify (0.3227 oz/1,000ft²) with 2 and 3 application frequency, Todal and Divamen provided increased in-season control of Mesocriconema nebraskense. In-season control of Meloidogyne was present only with 2 applications of Indemnify at the high rate. Looking at carryover efficacy, plots previously treated with 3 applications of the high rate of Indemnify had lower presence of M. nebraskense and Meloidogyne sp. as grass emerged from dormancy the following spring.

An analysis is being performed regarding winter Cover crop and nematode communities. The integration of winter cover crops (WCC) into an annual crop rotation has been shown in other environments to provide numerous soil ecological services, limit external input requirements and promote sustainability in many aspects of agriculture. In arid, irrigated systems, this practice may compete with irrigation demands of the cash crop and increase costs of farm operations through water availability and pumping costs as well as costs of labor. A study was initiated this year to address these issues. The objectives are to: (1) Determine the minimum water usage needed to produce a cover crop stand of adequate biomass to provide soil ecosystem benefits and (2) Assess impacts of irrigation regimes and cover crops on cash crop yields, soil quality indicators and soil pests. Data from these objectives will be used to select the cover crops and irrigation programs that are promising for ecosystem services while minimizing water use and farm operation costs.

Three cover crops are being evaluated: Austrian winter pea (Pisum sativum subsp. sativum), barley, mustard (Sinapis alba X Brassica juncea var. Caliente 199), and a mix of all three. Five regimes of flood irrigation include: (1) a single fall irrigation after planting, (2) single fall and spring irrigations, (3) a single fall irrigation with two spring irrigations, (4) two irrigations in the fall and one in the spring and (5) two irrigations in both fall and spring. Plots have been arranged in a randomized complete block design, replicated four times, and each block is paired with a non-irrigated fallow check plot. This study is being conducted concurrently at Ag. Science Research Centers in southern and central New Mexico over two years, applying the same irrigation and cover crop treatments to the same plots each year. A cash crop of sweet corn (Zea mays) will be planted in all plots in both years. Biotic and abiotic response variables being measured to assess cover crop and irrigation impacts include: nematode community dynamics, weeds within cover crops, weed winter seedbank dynamics, soil suppressiveness to fungal disease (Verticillium dahliae and Phytophthora capsici), phospholipid fatty acid (PFLA) analysis of soil, permanganate oxidizable carbon, dry aggregate size distribution and wet aggregate stability, pH, electrical conductivity, macronutrients, micronutrients, organic matter and cation exchange capacity.

The efficacy of new products in mint has been examined. Field, microplot, and greenhouse trials were conducted to determine chemical efficacy of several nematicide products against lesion, Northern root-knot (NRKN), and pin nematode on mint at the University of Idaho Research and Extension Center, Parma. The products tested, Velum Prime (fluopyram), Movento 240 SC (spirotetramat), and Vydate-L (oxamyl) showed moderate efficacy against lesion nematode over time, but little impact against NRKN or pin nematode. Additionally, two fungicidal products (Velum Prime, Elatus) were tested against Verticillium dahliae in greenhouse and field conditions. Neither was effective in managing verticillium wilt disease.

The chemical efficacy of several new products against Southern RKN in greenhouse tomato have been examined. Greenhouse trials were developed to determine the efficacy of several new numbered products from Marrone Bio and Gowan for Southern root-knot nematode (SRKN) control in greenhouse tomato. The Marrone Bio product failed to provide significant control of SRKN, while the Gowan product reduced nematode counts in the soil and root tissue by significant margins- roughly a 50% reduction on average.

Management strategies for Columbia RKN and lesion nematode in potato have been examined. Chemical efficacy of new non-fumigant chemistries and formulations, soil surfactant additives for fumigation, and several combinations of fumigants + non-fumigants were tested on potato in field conditions to determine management strategies for Columbia root-knot and lesion nematode. Fumigation of Telone II and Vapam HL proved extremely effective this year, reducing CRKN populations by 99% and reducing incidence of tuber infection to 3% or less despite high initial nematode populations. Non-fumigant nematicides did not fare as well against CRKN, showing no statistically significant differences in infected tuber counts from untreated controls. Treatments with Velum Prime and Vydate C-LV showed significant increases in yield when applied to lesion nematode-infested soil.

Sugar beet cyst nematode management strategies in sugar beet have been examined. A green manure study and several chemical efficacy trials were conducted in field and greenhouse conditions to determine potential management of SBCN on beet yield and sugar production. Neither green manure treatments nor chemical treatments produced significant differences in sugar beet yields in field trials. Greenhouse chemical efficacy trials revealed two new numbered compounds from Gowan and Bayer that had significant impacts against SBCN.

New nematode records have been made. The alfalfa cyst nematode Heterodera medicaginis was found in samples from Kansas, Montana, and Utah. This is the first time alfalfa cyst nematode has been found in North America. The cactus cyst nematode, Cactodera cacti, was found in Idaho and Colorado, a first for these two states.

There has been a possible new turf Meloidogyne species or first report of M. marylandi occurring in New Mexico. Co-occurring in this study with Mesocriconema nebraskense, the Meloidogyne sp. present shares only a 92-93% identity to other isolates of M. graminicola (COII) (personal communication (Dr. Tom Powers-University of Nebraska). It is however, a 99% match to a turfgrass-Meloidogyne spp. recently found in Georgia that has been reported as M. marylandi. (G. B. Jagdale et al., Disease Notes [2019]). Dr. Paulo Vieira (Virginia Tech) has been further analyzing DNA sequences of our isolate and found it to share 99 to 100% identity on 18S+ITS and 28S D2/D3 with that of the isolate from Georgia but has only 93% identity and two to four gaps on COII-16S with many sequences of M. marylandi in GenBank. More isolates of M. marylandi are being evaluated for comparison. Physical cultures have been sent to Dr. Jon Eisenback (Virginia Tech) for morphological analysis.

An unknown Rotylenchulus sp. has been recovered from the NMSU Leyendecker Plant Science Research Center, Las Cruces, NM with an affinity for corn. BLAST queries of the sequenced DNA (COII) indicate the isolate does not have a match in the GenBank database. It is not R. reniformis (86% match), R. parvus (87% match), or R. macrosoma (86% match) (personal communication, T. Powers-University of Nebraska). This unknown Rotylenchulus sp. has been isolated and is being grown in the greenhouse for morphological evaluation of all life stages.

A turf project has been performed to evaluate the Unmanned Aerial Systems (UAS) for its ability to detect plant-parasitic nematode damage in turf grass through the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Red Edge Index (NDRE) in conjunction with nematicide applications.  Both of the indexes used in this study are closely associated with plant health.  In 2018, microplot trials were conducted on ‘TifWay 419’ hybrid bermudagrass. Individual microplots had previously been inoculated with either Meloidogyne incognita or Belonolaimus longicaudatus. Nematicides included Multiguard Protect (furfural), Nimitz Pro G (fluensulfone), Divanem (abamectin), Indemnify (fluopyram), and an untreated control as a comparison.  Image analysis was collected via a DJI Phantom 4 equipped with a Micasense RedEdge-M camera at three time points: prior to nematicide treatment, 30 days after treatment (DAT), and 60 DAT.  Nematode population counts per 100 cm³ of soil were also taken the same time as image collection from each plot.  Data were analyzed using analysis of variance (SAS 9.4), and means were compared using the Dunnett’s statistic with P ≤ 0.05.  All nematicides led to a significant reduction of M. incognita at 30 DAT, and all but abamectin led to a significant reduction of B. longicaudatus at 30 DAT (P ≤ 0.05).  At 60 DAT, fluopyram was significantly lower than the untreated control in both nematode populations (P ≤ 0.05). Abamectin had a significantly lower M. incognita population compared to the untreated at 60 DAT (P ≤ 0.05). All other nematicides were statistically similar to the untreated at 60 DAT (P ≤ 0.05).  All treatments except furfural saw a significant increase in NDVI and NDRE values compared to the untreated control at 30 DAT, indicating an increase in plant vigor (P ≤ 0.05). At 60 DAT, only fluopyram had a significantly higher NDVI value compared to the untreated, and NDRE values were statistically similar across all treatments. Overall, all nematicides were effective at lowering both M. incognita and B. longicaudatus populations, and positive trends were observed for both NDVI and NDRE indexes for plant health analysis. This data shows that NDVI and NDRE can be valuable vigor assessments for tracking nematode populations in turfgrass.

The interactions between the RKN and fusarium (Fusarium oxysporum) have been investigated. The overall objective of the study was to evaluate the presence of FOV races in a cotton (Gossypium sp.) field and document the effects of M. incognita population density and resistance traits of the cotton.  A total of 132 isolates of FOV were collected throughout the season which represented 7 different races.  The most prominent race of FOV collected from the field was race 1, a race known to have a strong interaction with M. incognita. The highest nematode population density was recorded on the two Pima cotton varieties included in the test, Phytogen 800 and Pima S7 (2069 and 1539 eggs/g of root respectively). However, low rates of FOV infection, 8% on Phytogen 800 and 4% on Pima S7, were recorded on these varieties which may be due to resistance traits to FOV that are possessed by these varieties.  The highest infection rate of FOV (16%) was recorded on Rowden variety of upland cotton which also supported the highest M. incognita population density (316 eggs/g of root) of any upland cotton varieties.  A similar rate of FOV infection (14%) was recorded on the upland cotton variety of DP 1558NR B2XF.  This is a M. incognita resistant cotton variety that supported low population density of nematodes; however, the variety is also susceptible to FOV. This result demonstrates that nematode resistance alone is not sufficient to protect against FOV.

It is well known that Rotylenchulus reniformis causes yield loss in cotton across the mid-south and southeastern region. Further experiments have been performed with the objective being to quantify the yield loss due to R. reniformis and document any yield increase from the addition of a nematicide. Field trials were established in two adjacent fields, one was infested with R. reniformis and one where R. reniformis was not detected. In both fields, seven cotton cultivars were planted with and without Velum Total (1.02 L/ha). In 2017, R. reniformis reduced cultivar yields by an average of 59% between the non-infested and the R. reniformis infested field. The nematicide application increased seed cotton yields in the R. reniformis field by 55% and no yield increase was observed in the non-infested field. In 2018, R. reniformis reduced seed cotton yields by an average of 42% between the non-infested field and the R. reniformis infested field. Across the cultivars addition of the nematicide increased seed cotton yields by an average of 6% in the R. reniformis infested field and an average of 8% in the non-infested field. The nematicide reduced R. reniformis eggs per gram of root by an average of 92% in 2017 and 78% in 2018 across all cotton cultivars.  Overall R. reniformis reduced seed cotton yields by 50% which was equivalent to 2,225 kg/ha.   

Plants recognize nematode infections during root penetration, before initiating an elaborate feeding site characteristic of sedentary endoparasitic nematodes, and initiating a strong immune response. This immune response, known as pattern-triggered immunity, is tightly regulated. Tight regulation is necessary to control runaway immunity that may cause uncontrolled cell death or autoimmune disease. Such controls, also known as negative regulators of immunity, have been identified in Arabidopsis thaliana, orthologs are which are also present in crops including tomato. The absence of one such negative regulators results in enhanced resistance to the root-knot nematode, Meloidogyne incognita, in A. thaliana. To develop a similar resistance in tomato, tomato orthologs of the A. thaliana gene were targeted for mutations using clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 gene editing. CRISPR-Cas9 vectors used for editing tomato were used to develop constructs to edit two different tomato homologs of the negative regulator of immunity. Constructs targeting the individual genes or both genes together, using two guide RNAs for each, were developed and used in Agrobacterium/Rhizobium rhizogenes transformation of tomato cotyledons. Hairy roots induced by A. rhizogenes transformation were evaluated for deletions in the targeted genes using PCR. Our results indicated high efficiency in deletion in one of the targeted genes and lower efficiency in the second gene. No transgenic roots were identified with deletions in both genes suggesting either low mutation efficiency or lethal phenotype when both genes are eliminated. The successful constructs are currently being used to develop stable transgenic gene edited tomato plants for evaluation with nematodes.

Plants have an intrinsic ability to protect themselves from parasitic nematodes. However, processes relating to the nematode circumvent these defense processes. To examine if it is possible to activate these intrinsic plant defense processes in a normally susceptible host, laser microdissection has been done on Glycine max (soybean) root cells prior to and after parasitism by H. glycines. Hundreds of genes have been determined to be expressed specifically within the cells that are parasitized by H. glycines, but are undergoing a defense response. Prior work has shown the bacterial effector harpin effectively decreases parasitism by M. incognita, R. reniformis and H. glycines. Harpin treatment results in the activated transcription of a membrane receptor called NON-RACE SPECIFIC DISEASE RESISTANCE 1 (NDR1) which functions in defense to plant parasitic nematodes. NDR1 has been shown in new experiments to activate mitogen activated protein kinase (MAPK) signaling in the G. max-H. glycines pathosystem that leads to a defense response. In G. max there are 32 MAPKs. Transgenic experiments show that 9 of the 32 MAPKs function in defense. Illumina® RNA sequencing of the 9 MAPK overexpressing and also the 9 MAPK suppressing (by RNA interference [RNAi]) transgenic lines have led to the identification of over 450 candidate defense genes. Experiments are being performed to determine what role they perform in resistance to H. glycines. More broadly, many of these genes are highly conserved between different taxonomic groups of plants so it is likely that the types of genes identified in the G. max-H. glycines pathosystem will be relevant to the discovery of defense genes in other agriculturally relevant crops species.

Impact Statements

• Novel plant receptors involved in recognition and response to nematode infection have been identified.
• Continued efforts are being made to refine and define the conditions and limitations DNA barcoding using the COI mitochondrial gene.
• Barcoding surveys on a large geographic scale will help establish species boundaries of plant parasitic nematodes.
• A field device for rapid identification of cyst nematode juveniles could accelerate the time and reduce the expense of species identification.
• Global assessments of nematode abundance and community trophic structure will aid in monitoring below ground changes due to environmental conditions.
• Mixing the soil with a spader tiller after shank injection of metam sodium did not improve control of tuber damage from Columbia root-knot nematode (Meloidogyne chitwoodi).
• A new oxamyl product, ReTurn XL, was equal to Vydate C-LV at suppressing tuber damage from CRKN.
• Using Velum Prime (Fluopyram) in-furrow was as good as using Vydate in-furrow.
• No treatments were effective if they did not have either Vydate or Velum Prime in-furrow.
• Replacing two mid-season Vydate applications with Movento (Spirotetramat) did not reduce the level of control.
• preplant incorporated (PPI) application of Nimitz (Fluensulfone).alone had no effect on the level of culled tubers but appeared to be of benefit when used before a full season program consisting of an in-furrow application of Velum Prime (or presumably Vydate) and the complete in-season Vydate program.
• There are several reasons to use Velum Prime in-furrow rather the oxamy1: (a) Velum Prime is less toxic than oxamyl so growers may be more inclined to use it in-furrow, (b) Velum Prime may be marginally better than oxamyl, (c) Allows one or two more in-season applications of oxamyl before the allowable a.i. is reached
• Overall, our molecular studies on resistance in potato combined with our work on the genetic variability of different chitwoodi races has given us insights into the genetic factors involved in plant-nematode interactions.
• The experiments establish a basis for identifying the biotic and abiotic factors of nematode adaptation and parasitic variability that lead to understanding biological interactions and developing location-specific solutions.
• The experiments develops new knowledge on natural host resistance traits to manage root-knot nematodes in field and vegetable crops, which can be adopted by plant breeding programs and the seed industry to benefit growers by producing nematode resistant crop varieties.
• Normalized Differences Vegetation Index (NDVI) and Normalized Difference Red Edge Index (NDRE) can be valuable vigor assessments for tracking nematode populations in turf.
• Root knot nematode resistance in cotton will not eliminate FOV disease incidence.
• The reniform nematode reduced cotton yield potential in half even with nematicide applications.
• Growers plant healthy fields first and wash equipment after leaving a nematode infested field.
• Understanding how plant immunity is regulated to resist nematode infection will lead to better engineering crops with broad-spectrum and durable resistance.
• Understanding the genetic basis of resistance in one plant can be used as an effective tool for identifying the underlying conserved mechanism of resistance in other important crop species.

Publications

Acar I, Sipes S. 2019. Enhancing the biological control potential of entomopathogenic nematodes protection from desiccation and UV radiation. Biological Control (Submitted).

Alshehri HA, Alkharouf NW, Darwish O, McNeece BT, Klink VP. 2019. MAPKDB: A MAP kinase database for signal transduction element identification. Bioinformation 15:338-341. DOI: 10.6026/97320630015338.

Austin HW, McNeece BT, Sharma K, Niraula PM, Lawrence KS, Klink VP. 2019. An expanded role of the SNARE-containing regulon as it relates to the defense process that Glycine max has to Heterodera glycines. Journal of Plant Interactions 14:276-283. DOI: 10.1080/17429145.2019.1622043.

Disi JO, Mohammad HK, Lawrence K, Kloepper J, Fadamiro H. 2019. A soil bacterium can shape belowground interactions between maize, herbivores and entomopathogenic nematodes. Plant Soil 437:83–92.  DOI.org/10.1007/s11104-019-03957-7.

Eisenback JD, Holland LA, Schroeder, J, Thomas S, Beacham JM, Hanson SF, Paes-Takahashi VS, Vieira P.  2019.  Meloidogyne aegracyperi n. sp. (Nematoda: Meloidogynidae), a root-knot nematode parasitizing yellow and purple nutsedge in New Mexico.  Journal of Nematology 51: DOI: 10.21307/jofnem-2019-071.

Groover W, Lawrence KS, Donald P. 2019. Reproductive rate differences of root-knot nematodes from multiple crops in a single field. Nematropica 49:00-00 (In press).

Hall, M. Lawrence KS, Shannon DA, Gonzalez T, Newman M. 2019. Southern root knot nematode (Meloidogyne incognita Kofoid and White) Chitwood susceptibility to tumeric (Curcuma longa L.) accessions. International Journal of Applied Research on Medicinal Plants 2:007. DOI:10.29011/IJARMP-107.100007.

Lonardi S, Muñoz-Amatriaín M, Liang Q, Shu S, Wanamaker SI, Lo S, Tanskanen J, Schulman AH, Zhu T, Luo M-C, Alhakami H, Ounit R, Hasan AM, Verdier J, Roberts PA, Santos JRP, Ndeve A, Doležel J, Vrána J, Hokin SA, Farmer AD, Cannon SB, Close TJ. 2019. The genome of cowpea (Vigna unguiculata [L.] Walp.). The Plant Journal 98:767–782. DOI: 10.1111/tpj.14349.

Marquez J, Sipes B, Cheng Z, Wang K-H. 2019. Enhancement of indigenous entomophathogenic nematodes by no-till cover cropping with black oat (Avena strigose) in a corn (Zea mays) agroecosystem. Biological Control (Submitted).

McNeece BT, Sharma K, Lawrence KS, Lawrence GW, Klink VP. 2019. The mitogen activated protein kinase (MAPK) gene family functions as a cohort during the Glycine max defense response to Heterodera glycines. Plant Physiology and Biochemistry 137:25–41. DOI.org/10.1016/j.plaphy.2019.01.018.

Ndeve AD, Santos JRP, Matthews WC, Huynh BL, Guo Y-N, Lo S, Muñoz-Amatriaín M, Roberts PA. 2019. A novel root-knot nematode resistance QTL on chromosome Vu01 in cowpea. G3 (Genes, Genomes, Genetics) 9:1-11. DOI: 10.1534/g3.118.200881.

Ozbayrak M, Todd T, Harris T, Higgins R, Powers K, Mullin P, Sutton L, Powers T. A COI DNA barcoding survey of Pratylenchus species in the Great Plains region of North America. Journal of Nematology.  51:e2019-81. DOI: 10.21307/jofnem-2019-081.

Powers T, Skantar A, Harris T, Higgins R, Mullin P, Hafez S, Handoo Z, Todd T, Powers K. 2019. DNA barcoding evidence for the North American presence of alfalfa cyst nematode, Heterodera medicaginis. Journal of Nematology 51:1–17. DOI: https://doi.org/10.21307.

Skantar AM, Handoo ZA, Kantor MR, Hult MN, Hafez SA. 2019. First report of the cactus cyst nematode, Cactodera cacti from a cactus garden in Idaho. Journal of Nematology 51:1-6. DOI: https://doi.org/10.21307/jofnem-2019-044.

Van Den Hoogen, J, Geisen, S, Routh D, Ferris H, Traunspurger W, Wardle DA, De Goede RGM, et al. 2019. Soil nematode abundance and functional group composition at a global scale. Nature 572:194-198. DOI: 10.1038/s41586-019-1418-6.

Zasada IA, Ingham RE, Baker H, Phillips WS. 2019. Impact of Globodera ellingtonae on yield of potato (Solanum tuberosum). Journal of Nematology. 51:2019-073. https://doi.org/10.21307/jofnem-2019-073.

Zasada IA, Kitner M, Wram C, Wade N, Ingham RE, Hafez S, Mojtahedi H, Chavoshi C, Hammack N. 2019. Trends in occurrence, distribution, and population densities of plant-parasitic nematodes in the Pacific Northwest of the United States from 2012 to 2016. Plant Health Progress. 20:20-28. https://doi.org/10.1094/PHP-11-18-0077-RS.

Abstracts, Proceedings, Conferences and Reviews

Brown JK, Avelar S, Schrimsher DW, Conner K, Jacobson A, Lawrence K. 2019. Identification of a Cotton Leafroll Dwarf Virus- Like polerovirus infecting cotton in Alabama during 2017-2018. Proceedings of the 2019 Beltwide Cotton Conference 1:40-46. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Dyer D, Lawrence KS. 2019. Effect of Meloidogyne incognita populations density on the prevalence of Fusarium oxysporum f. sp. vasinfectum races. Journal of Nematology 51: (In press).

Dyer D, Lawrence KS. 2019. Use of a Liquid Fertilizer (AgraLi) to Reduce Rotylenchulus Reniformis Population Density and Increase Cotton Yields. Proceedings of the 2019 Beltwide Cotton Conference 1:363. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Dyer DR, Lawrence K, Aida M. 2019. Evaluations of the temporal and spatial occurrence of Fusarium oxysporum f. sp. vasinfectum races as influenced by selected cotton genotypes in the National Cotton Fusarium Wilt evaluation field in Alabama. Proceedings of the 2019 Beltwide Cotton Conference 1:364-371. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Faske TR, Allen TW, Grabau Z, Kemerait R, Lawrence KS, Mehl HL, Overstreet C, Thiessen LD, Wheeler TA. 2019. Beltwide Nematode Research and Education Committee Report on Field Performance of Seed-Applied and Soil-Applied Nematicides, 2018. Proceedings of the 2019 Beltwide Cotton Conference 1:364-371. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Gattoni K, Xaing N, Lawaju BR, Lawrence KS, Kloepper JW. 2019. Systemic response stimulated by Bacillus spp. can manage Meloidogyne incognita population density in Gossypium hirsutum. Proceedings of the 2019 Beltwide Cotton Conference 1:114-122. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Gattoni K, Xiang N, Lawaju B, Lawrence KS, Park SW, Kloepper JW. 2019. Potential mechanism of action for Bacillus spp. inducing resistance to Meloidogyne incognita on cotton. Journal of Nematology 51: (In press).

Giese WG, Beacham JM, Velasco-Cruz C, Thomas SH, Powers TO. 2019.  Nematode occurrence, frequency, relationships and correlations in New Mexico vineyards. Journal of Nematology 51: (In press).

Groover W, Lawrence KS, Dyer D. 2019. Yield loss of cotton cultivars due to the reniform nematode and the added benefit of Velum Total. Proceedings of the 2019 Beltwide Cotton Conference 1:333-336. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Groover W, Lawrence KS. 2019. Unmanned aerial system imagery analysis of modern turf grass nematicides. Journal of Nematology 51: (In press).

Guyer RR,  Newman MS, Kelly H, Allen TW, Sciumbato G, Wilkerson TH, Barham JD, Barnett W, Beach A, Keiser AR, Bayles MB, Verhalen LM, Caceres J, Lawrence GW, Colyer PD, Kelley T, Thacker R, Kemerait RC, Lawrence KS, Mehl HL, Phipps PM, Padgett G, Price P, Rothrock C, Winters S, Schuster G, Spurlock T, Woodward J. 2019. A historical review of the national cottonseed treatment program: 1995-2017. Proceedings of the 2019 Beltwide Cotton Conference 1:587-591. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Heather K, Guyer RR, Pate SN, Allen TN, Wilkerson TH, Bayles MB, Colyer PD, Lawrence KS, Mehl H, Price P, Spurlock T, Woodward J, Cartwright ML. 2019. Report of the Cottonseed Treatment Committee for 2018. Proceedings of the 2019 Beltwide Cotton Conference 1:577-584. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Kaloshian I, Teixeira M. 2019. Advances in plant−nematode interactions with emphasis on the notorious nematode genus Meloidogyne. Phytopathology 109:1988-1996. DOI: 10.1094/PHYTO-05-19-0163-IA.

Klink VP. 2019. A developmental genomics analysis of soybean defense processes. Plant and Animal Genomes Meeting XXVII. San Diego, CA.

Klink VP. 2019. The use of crop functional developmental genomics to enhance undergraduate education. 83^rd Mississippi Academy of Sciences Annual Meeting-Science Education Section, Hattiesburg, MS.

Klink VP, McNeece BT, Sharma K, Niraula P, Troell HA, Khatri R, Adhikari M, Acharya S. 2019. A functional genomics analysis of 20 S particle proteins in Glycine max as it resists infection by the plant parasitic nematode Heterodera glycines. American Society of Cell Biologists. Washington DC.

Lartey I, Marsh TL, Melakeberhan H. 2019. Soil type-driven foodweb dynamics associated Meloidogyne hapla in Michigan vegetable fields. Society of Nematologists 58th Annual Meeting. Raleigh, NC. 57.

Lawrence KS, Jacobson A, Sikora E, Hagan A, Conner K, Schrimsher D, Brown JK. 2019. Cotton Leafroll Dwarf Virus – A Polerovirus identification, symptomatology, and occurance in Alabama. Proceedings of the 2019 Beltwide Cotton Conference 1:125-128. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Lawrence KS, Sandlin T, Raper TB, Butler S, Kelly H, Meyer B, Silvey N. 2019. Cotton cultivar disease incidence, severity, and yields when challenged with Verticillium Wilt in the Tennessee Valley Region, 2018. Proceedings of the 2019 Beltwide Cotton Conference 1:129-132. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Lawrence KS, Hagan A, Norton R, Hu J, Faske TR, Hutmacher RB, Mueller J, Small I, Grabau ZJ, Kemerait RC, Price P, Allen TW, Atwell S, Idowu J, Thiessen LD, Byrd SA, Goodson J, Kelly H, Wheeler T, Isakeit T Mehl HL. 2019. Cotton Disease Loss Estimate Committee Report, 2018. Proceedings of the 2019 Beltwide Cotton Conference 1:54-56. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Luff K, Hafez SL.  2019. The use of new chemistries for potato nematode management programs in Idaho, USA. Society of Nematology, South Carolina.

Nunes MN, Lawaju B, Groover W, Dyer D,  Gattoni K, Sanchez W, Lawrence KS. 2019. Nematicide application through drip irrigation systems for Southern Root-knot nematode management. Journal of Nematology 51: (In press).

Park, SW, Liu W, Jones AL, Gosse HN, Lawrence KS. 2019. Root exudates convey host-specific messages that control the short-range underground orientation of plant parasitic nematodes. Journal of Nematology 51: (In press).

Pate SN, Kelly H, Guyer RR, Lawrence KS, Allen TW, Bayles MB, Colyer PD, Mehl H, Price P, Spurlock T, Woodward J. 2019. Current methods of the national cottonseed treatment program and proposed changes in protocol.  Proceedings of the 2019 Beltwide Cotton Conference 1:548-551. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Rondon MN. Lawaju BR, Lawrence KS. 2019. In vitro effect of fungicides on Corynespora cassiicola isolates from cotton and soybean in Alabama. Proceedings of the 2019 Beltwide Cotton Conference 1:151-156. National Cotton Council of America, Memphis, TN. http://www.cotton.org/beltwide/proceedings/2005-2019/index.htm.

Sanchez, WD, Williams G, Lawrence KS. 2019. Efficacy of entomopathogenic nematodes on small hive beetles (Aethina tumida) in kalmia loamy sand. Journal of Nematology 51: (In press).

Zhang L, Gleason C, 2019. Bacterially secreted defense peptide StPep1 stimulates root-knot nematode resistance in potato. The XVII Congress on Molecular Plant-Microbe Interactions, Glasgow, Scotland.

Zhang L, Gleason C, 2019. Engineering bacteria as delivery agents of the defense-inducing peptide StPep1 improves root-knot nematode resistance in potato. Society of Nematologists 58th Annual Meeting. Raleigh, NC.